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Frew Oasys GEO Suite for Windows

1. 8 2 1 4 Groundwater 2 522 9 20 08 C68 003 coa 10 2 2 11 23 5 oua 12 2 1 Safe Methiotl UE 13 23 Mindlin 13 2 3 3 Method 14 24 Active and Passive 15 2 4 1 Effects of Excavation and Backfill 1 nnn nnne n nnn nnn nh nna renun nra 16 2 4 2 Calculation of Earth Pressure Coefficients 1e cereo eren nnne nnne nnn 16 2 5 Total and 2 REF M EERE S US REM E SER EU RRE NEU USER M DESEE 18 2 5 1
2. ee Sese x 1 236 423 Restraints The following points should be noted regarding the export of data related to restraints 1 All restraints in the model are of pin type and are applied at the rigid boundaries 2 The restraints are constant across all stages Variable boundary distances across different stages not supported Oasys Ltd 2014 Frew Safe Link 42 4 Surcharges The surcharges are applied as element edge loads in the corresponding stages Frew surcharge data Manual fwd Surcharges Stage i 5 Tey CETT Offset Width 30 00 Strip Equivalent Safe element load data Pressure Loads PT Defaults E Aol 20 00 20 00 585 2 Normal 25 00 25 00 3 1 hk d 4 2 5 Struts otruts in Frew modeled as springs in Safe and act at nodes located on the wall axis Lever arm information is not exported from Frew to Safe Pre stress is applied as a node load in Safe The prestress along the spring axis direction is resolved into components along the X and Y axes and applied as a pair of node loads in Safe Frew strut data Frew Manual fwd Struts __ _ B C Strut Node Prestress a arm mt p ga umber T m Defaults Equivalent Safe stru
3. IE Rae 33 34 9 Material amp 34 344 eua cuo caves dover acne dd ele D T LUPUS 37 9 4 9 StUr b PRO PCT UG S eadein e reci Cota 41 3 4 5 1 Modellitig oT lobe ero tear bti iet es optinere 43 346 eh coni acta S boo idit DE 44 Oasys Ltd 2014 Contents 3 4 6 1 Application of Uniformly Distributed 2 45 3462 Applcaliopnorestrip 20896 Acces wh ou ede Fel Asin cede dou ets 45 SE STA Partal ECT 47 3 4 8 Node generation n e t Veto Nen Iani Fe cedi vast i les koc ded 50 3 5 Stage Data teet 51 3 9 1 Stage 0 Tritidl GCondltlOHs Fou 52 RROPAMS DA UEDZCBAIIDMMES S NS e 52 3 5 3 Inserting Stage S casn isa Sese undi asi RN c D UNE DM 53 3 94 Del tilid d SIage aceite hte RS annia Sul Cub totius Lodi ox nan Deacon docilis m d
4. CHO UE Tes 145 8 6 LLL em 145 5 9 1 Rigorous Method unde cn HL ES 146 8 92 LLLI SD 148 9 9 Creep and BelaxallOn icona co oe eae E M nM ERE E UNUS 149 8 9 1 Changing From Short Term to Long Term Stiffness esee e nennen nnne nnam nnn 149 8 10 Undrained to drained behaviour Manual Process 151 8 10 1Undrained to Drained Examples 4 2 4 1 11 4404 404040404044 4 002000 0240000 01101 6 141018108100 ESAE AAA aeaa E SENERE 152 9 List of References 158 91 Referents RR 158 10Brief Technical Description 159 10 1 Suggested Description for Use in Memos Letters etc 159 10 2 Brief Description for Inclusion in Reports 41 1 159 11Manual Example 160 General Dm 160 Index 161 Oasys Ltd 2014 Frew Oasys GEO Suite for Windows 1 About Frew 11 General Program Description Frew Flexible REtaining Walls is a program that analyses flexible earth retaining structures such as sheet pile and diaphragm walls The program enables the user to study the deforma
5. Calculated ed Deeds 50000 200 0 60 UserSpeciled 020 6 00 0894 4899 02 000 00 000 000 Drained 2 Material 2 25001 130 0 80 User Specified 0 35 350 1183 374203 1000 00 000 000 Drained Equivalent Safe Mohr Coulomb material data Safet Elastic Mohr Coulomb material properties ji Gradient Strenath Zune Description MS Strength a m 01807 11 9 one 0 gemmam 000000004 Angle of friction is the average of values obtained from the following expressions for coefficients of active and passive pressure l sin e K LUE lsm g The angle of friction is limited to a maximum value of about 50 degrees Oasys Ltd 2014 Frew Oasys GEO Suite for Windows 4 2 6 1 First Stage Material In Safe as discussed earlier the initial ground stresses are calculated using two parameters KO and 9 The slope of the effective vertical soil stress profile is the effective unit weight of the material KO determines the slope of the effective horizontal stress profile and g is the reference level for the linear stress distribution i e the level at which the vertical or horizontal stresses are zero see figure below Level y 4 Effective Vertical Ground level Stress ay zone 1 Z Water table zone 2 Increase of density zone 3 When a soil stratum is p
6. 87 4 28 Unsupported PO Ati eS 88 5 Integral Bridge Analysis 88 NEP 89 D2 AIGOMNMS E 93 6 Seismic Analysis 93 Oasys Ltd 2014 Frew Oasys GEO Suite for Windows ed icc 94 6 2 Seismic Analysis 96 6 2 1 Calculation of Seismic Soil Pressure Coefficient 96 622 Wood Died ue Poe 96 62 3 Mononobe Okabe Method iui 97 6 24 Load Applicaton Methods oto ti Hautes sr tt nh hadas iie Ue DE DERE 100 6 25 Groundwater Ya tu bru DR ona 101 7 Output 101 7 1 Analysis and 101 142 S 104 Stability Check Besults ioni 106 722 Detailed
7. i gt e stage number at which the strut is inserted e The stage number at which the strut is removed leave blank if the strut is still active during the final stage e The level at which the strut acts if using automatic node generation or the node number if using manual node entry e Any pre stress force applied i e force in the strut when it is inserted e 515 stiffness i e change in force AF kN in strut for a unit AU 1m movement at it s point of application both measured along the axis of the strut per m run of wall K AF AU Cross sectional area of strut E Young s modulus L Length of strut Stiffness R AP AU The angle degrees to the horizontal ve anticlockwise e A moment can be applied to the wall by using a strut at an angle of 90 degrees and a lever arm i e distance from neutral axis of wall to point of application of strut ve to the right Oasys Ltd 2014 8 Frew Oasys GEO Suite for Windows 3 4 5 1 strut PFrestress Ps stiffness 55 Angle a Note More than one strut may be defined at a particular node and not all struts need to act simultaneously If a strut is inserted in Stage O prior to the wall being installed only the horizontal pre stress force is modelled The stiffness of the strut will be modelled in subsequent stages An applied moment or a moment restraint at a node can be modelled by usin
8. 1 4 2 20 kM m I L L r x 12329 y 123228 gt n c 2 Oasys Ltd 2014 Frew Oasys GEO Suite for Windows m Level Lett Hight Node m material material Mane Material 19 00 19 00 17 00 16 00 15 00 14 00 13 00 12 00 11 00 10 00 9 00 7 Lr 6 00 5 00 4 00 3 00 2 00 1 00 0 00 FEIN 3 i LEN 8 EMEN i0 a 13 d4 1 i5 dB 18 18 20 Material Material Material Material Material Material Material Material Material Material Material Material Material Material Material Material Material Material r2 r3 m Material Material Material Material Material Material aerial Material Material Material Material Material Material Material Material Material Material Material Material Material Po m3 ra m ra m rm rm In addition to placing nodes at key locations in the construction sequences it is also important to space them at
9. E 0 000001 70 000000 0 000005 68 000000 65 000000 Ts 51 000000 0000100 43 000000 i5 0000500 23 000000 4 The user has to specify whether the integral bridge analysis needs to done at the front back of wall The user needs to specify the strut index which models deck contraction and expansion Preferably this strut should have only prestress and no stiffness During the integral bridge analysis cycles of contraction and expansion it will apply the prestress in this strut with appropriate sign Oasys Ltd 2014 Frew Oasys GEO Suite for Windows Frew 19 1 Winter2 AA 2lter D1p5 H10 fwd File Edit View Globaldata Stage data Analysis Tools Window Help eGR 1 El X n m i Input Titles Units Analysis location Global Behind wall Material properties 5 Node levels 45 Assumed initial values Strut properties 7 H behind wall Surcharges d behind wall Partial factors Node generation data H at front of wall Data for Stage 2 Apply remove surcharges Insert remove struts d at front of wall Convergence data Sod zones Tolerance on d H Water data Left 1 Maximum number of iterations Right 1 Wall data 44 Strut data Analysis method Index of strut modelling thermal expansion contraction Convergence control Integral bridg
10. Oasys Ltd 2014 Detailed Processes in Frew LAST UNDRAINED STAGE PARAMETERS Stage 2 C m e XL E E E E F3 Ca en on 03 1 2 J 4 5 i 10 1 1 1 1 1 1 1 a 2 3 4 5 B 9 0 PWP kPa 200 159 109 c ce 4 4 3 3 3 3 E 3 3 Total Del Se T otal Del Pe rJ TI i j E Lm I YE 18 3b 54 iz Pe Pe 10 20 30 50 Fr 10 1007 152 HEC 54b E 16 24 32 48 55 7 100 154 6 seb 120 1756 216 234 252 270 288 306 342 p 6 n 1 J B 5 4 3 2 1 386 CN _ Sy 162 234 NN 29 308 342 1 I I 1 50 eon Calculated Against Level 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 Level mOD Passive Pressures Oasys Ltd 2014 155 Frew Oasys GEO Suite for Windows STAGE 0 PARAMETERS MODE LEVEL Effectwe Effective User spect Total Total Fe T Ve 4 LL a
11. stage will be added after the current stage as shown on the Status bar Safe Runs m Frew Sate Link sfd Runs and Events Event 1 A Bun Initial Condition Event 2 A Run 2 Dewater AHS amp dig ta 27 5 mOD Event 3 A Aun 3 Stress anchor Event 4 A Aun 4 Lock anchor and to 24 6 Event 5 A Bun5 Install floor slabs and remove anchor Lleanup deletes results all increments except the last in the run Delete results deletes all the results of the curently selected run and its dependencies Oasys Lid 2014 Frew Oasys GEO Suite for Windows 42 2 Geometry For a given Frew model points are generated at locations corresponding to Material layer boundaries Groundwater levels e Surcharge levels e Strut locations e Wall end points e Rigid boundary intersections A series of lines connect these points in the form of a grid Areas are formed from these lines Once this geometry is created mesh generator is called if required by the user The node spacing is dense towards excavation levels Unlike in Frew the wall in Safe is made up of Quad 8 elements t Manual sfd Graphical Input Seles x 2200 2800 Orthogonal lines Snap interval 2 00 Number of divisions for new lines New line data Apply B m m 7 Fd 5 5 rH 1 E ul 2 1 1
12. Each Frew node below the current ground level position is assigned Frew element Boundaries occur mid way between nade adjacent Frew nodes FR E element Note Since the node spacing in Frew does not have to be uniform the node position is not necessarily at the mid point of the Frew element The boundaries of the Frew elements are mapped onto the Safe model The flexibility for a unit pressure over the Frew element length can then be determined This is achieved by summing the contributions at the Frew node position from all Safe elements Oasys Ltd 2014 115 Frew Oasys GEO Suite for Windows which contribute directly to the Frew element Frew Modes sate Modes MNT FRE element 7 4 6 FENNA NNT FENNA AMIN FENN NMIN 1 FINN T NN TJ FINNT x WTZ F NN2 NNA FINN2 NMIN 11 x WTT FNN NMAX FINN2 NN2 FNNA x WTZ F IN JN FINNI NN x b FINN2 NN2 x a NIMIN WT Mate Flexibility coefficient 1 represents displacement at node due to a unit load at node Weighting factors are used to account for the effect for loading from a partial Safe element if Frew element boundaries bisect a Safe element Using this procedure the equivalent total load acting on the Frew node corresponds to the length of the Frew element in multiples of the Safe element length Since the Safe coefficients wer
13. Material parameters use d in integral bridge analysis Right side HiBight 14 0241 m DiBight 0 58634 mm D HiBight 40 18E 6 Node Level Material Density Kac Koc index k a Lm m kPa 16 a u 2 24 50 0 2414 0 2059 0 9075 0 4690 1 370 52 04 B2424 H 17 0 5000 2 24 20 0 2414 0 059 0 9075 0 4690 1 270 52 04 247764 19 1 000 2 24 50 0 3414 0 2059 0 9075 0 4690 1 370 52 04 104500 i9 1 500 2 24 20 0 2414 0 2059 0 9075 0 4690 1 270 52 04 218076 2 0 00 2 24 20 0 3414 0 2059 0 9075 0 4690 1 53570 52 04 247275 21 2 500 2 24 20 0 2414 0 2059 0 9075 0 4690 1 270 52 04 273372 3 000 2 24 50 0 3414 0 2059 0 9075 0 4690 1 370 52 04 2971857 z3 3 500 2 24 20 0 2414 0 2059 0 9075 0 4690 2 970 52 04 319230 z 4 000 24 50 0 3414 0 2059 0 9075 0 4690 1 370 52 04 33598746 25 4 500 2 0 2414 0 2089 0 9075 0 4650 1 270 52 04 355282 5 000 2 24 50 0 3414 0 2059 0 9075 0 4690 1 370 52 04 377718 57 5 500 2 24 20 0 2414 20559 0 9075 4650 1 270 52 04 395256 zg 000 24 50 0 3414 0 2059 0 9075 0 4690 1 370 52 04 412124 z9 6 500 2 0 2414 0 9075 0 4650 1 270 52 04 20292 40 7 000 2 0 2418 0 2059 0 9075 0 4690 1 270 52 04 449871 31 7 500 2 24 20 0 2418 205595 0 9075 0 4650 1 270 52 04 458922 BH 0 00 2 24 20 0 24184 0 2059 0 9075 0 4 90 1 270 52 09 473495 33 d S 2 24 30 0 2418 20559 0 9075 0 49650
14. Material properties Partial Factors v Mode levels Strut properties v Surcharge properties The Global Data menu enables entry of the general data which is common to or accessed throughout the analysis The information can be entered in any order The exception is that the program requires Material properties to be entered before Node levels Stage Data Stage data Analysis Tools Open stage tree view Oasys Ltd 2014 Input Data 24 2 FREWman fwd Stage Operations Stage 0 Initial condition Stage 1 Insert wall in Undrained Conditio Stage 2 Apply Plant Loading on Active 51 Stage 3 Apply Anchor Prestress Stage 4 Apply Anchor Stiffness Stage 5 Excavate to Final Level 40 5 0 Stage b Apply Roof amp Basement Slab Str Stage 7 Undrained to Drained Stage B Undrained to Dramed Switch Se Stage 3 Undrained to Dirained PMP tac Stage 10 Remove Plant Loading Stage 11 Wall amp Strut Relaxation New stage will be added after the current stage shown on the Status bar The Stage Operations window or the B icon will allow individual stages to be modified When opened the Stage Operations view shows a tree diagram which allows access to all available options for each stage Ticks are placed against those options which have been changed This window also allows the creation of new stages of analysis and the deletion of stages that are no longer required Note Left click
15. Oasys Lid 2014 21 Frew Oasys GEO Suite for Windows 2 5 3 BYE CHE pal Bounding curt dred Ure pare Bardy irr I ow LLI d in LLI ZI in MEAN STRESS Pu Phy or Py PH Je Undrained Materials and User defined Pore Pressure In this procedure o and o are values which are used in the calculations for equilibrium whilst u may be a user specified value which does not change during deformation and is therefore not generally correct for true undrained behaviour Hence the results reported as V Vertical stresses and horizontal stresses are apparent rather than true effective stresses unless the program calculates approximate undrained pore pressures For undrained or partially drained behaviour where pore pressures change in response to movements a constant pore pressure component U0 defined by the user is thereby very unlikely to represent the actual pore pressure in the soil Approximate undrained pore pressures can be calculated by the program by setting an extra material parameter see Undrained Materials and Calculated Pore Pressures If this option is selected any data pore pressure distribution entered by the user is ignored in undrained materials There are two ways of representing undrained materials if undrained pore pressures are not being calculated A
16. 10 Left 50 00 m 10 00 1 10 2 Right 40 00 UBL 15 00 1 00 3 e stage number at which the surcharge is applied The stage number at which the surcharge is removed leave blank if the surcharge is still present in the final stage The side left or right of the wall where the surcharge is to be located The level The load type UDL or strip load The pressure The partial factor to be applied to the surcharge This will be applied only is partial factor analysis is specified by the user in Partial Factors dialog e Dimensions Offset Distance of the line of the wall to the nearest edge of the strip plus Width of the strip normal to the line of the wall These fields are not available for a udl e Ks used as discussed below 1 if the surcharge is narrow compared to the underlying soil layer Kr if the surcharge is very wide see Material Properties Note The chosen value of Kr to which Ks is equated should correspond to the material type that is most influenced by the transfer of the applied load to the wall If the layers are relatively thin then an average value should be taken If the stages include a change between undrained and drained Oasys Ltd 2014 Frew Oasys GEO Suite for Windows materials then multiple surcharges should be entered to take the change of Kr at the relevant stage into account The surcharge can be applied before the wall is inserted Stage 0 If this is the case the program computes
17. It is more likely that this method will be too conservative especially in frictional materials 0 gt 0 This is because the benefit of the weight of the berm has been disregarded in calculating passive pressures below the level b An allowance may be made for this by applying Steps 2 and 3 above at a slightly lower level above which the weight of the full depth of the berm will be experienced by the ground Better still Steps 2 and 3 can be applied incrementally over a few depths so that the adverse effect of the restricted length of the berm is applied gradually with depth When using this procedure it must be remembered that the force Fb is the passive force experienced within the height of the berm which is transferred as an adverse horizontal shear force to the ground beneath Therefore the additional passive resistance force in the ground beneath the berm due to the presence of the berm may be taken as where W is the weight of the berm This formula will need refinement if varies with depth Oasys Ltd 2014 Frew Oasys GEO Suite for Windows 6 9 8 9 1 Creep and Relaxation There is often a requirement to model creep in Frew Usually this refers to the creep of concrete structures which structural engineers normally represent by a change of Young s modulus However It cannot be represented so simply in Frew Elastic moduli are defined as ratios of stress to strain The stresses and strains used in
18. 30 00 Sandy clay 21 20 Material 2 14 90 Material 3 A Press lt gt En start a new record To edit a soil zone s material right click in the zone and choose the new material from the dialog To change the level of a soil zone or delete it simply edit or delete the record in the Material Layers table Note that there is a toolbar shortcut to specify excavation or filling Adding soil zones when using manual node entry Oasys Ltd 2014 Frew Oasys GEO Suite for Windows 57 Sees gt a rum ni 2 ni LL Ni Current selection Modes 10 5 LEVEES 4 12 ee eee 1 L 1 1 1 1 4 Scale x 1 240 w 1 335 STAGES Excavate to Final Level 4 5m00 amp Diewater Oasys Ltd 2014 input Data Left material material FREWman fwd Node Data m Level wmm Hode m node KN Defaut LEEREN 2 3 4 f B O 8 E io cc 12 13 d e 15 l6 Iz E INI aa 2a A 22 Ba 24 Soil zone data can be specified using the table by highlighting a cell and selecting the material type 50 00 49 00 49 00 47 00 46 00 45 00 44 00 43 00 42 00 41 00 40 00
19. Set exact scale Scaling Font Save image Input Results Set problem limits F w Toggle Strata Flot external x data Templates k Note When soil stiffness is represented using the Safe or Mindlin methods it is assumed that the lowest node specified in the data defines a horizontal rough rigid boundary The snap interval is also entered here This 5 the closest point onto which the cursor will lock to mark a point The snap interval is taken as the nearest interval in metres Adding nodes To add nodes select the Global data Node levels menu option or select the nodes button on the graphics toolbar Nodes can then be added by entering their level directly in the table or graphically by the following procedure 1 Use the mouse to place the cursor over the location of the top node 2 Click with left button on the location This will place the node on the line of the wall Note If the scale of the diagram is too small to locate the nodes accurately then maximise the main and graphics windows to increase the size of the image Editing the location of the node If the location of the node requires editing then this can be done in one of two ways 1 Place the cursor over the node and click the right mouse button This will bring up an amendment box Oasys Ltd 2014 Frew Oasys GEO Suite for Windows Mode level Level of node 4 rn 1188
20. Specified profile of pore water pressure e the pore pressure considered by the program can usually be regarded as the initial pore pressure before deformation whilst e The apparent horizontal effective stress P e becomes the sum of the true effective earth pressures and the excess pore pressures due to deformation o Au Oasys Ltd 2014 Methods of Analysis 22 B Zero pore water pressure profile e the value of apparent horizontal effective stress P can then be equated to the true total stress P 0 u In both these cases the values of and K should be set to unity 1 0 but with non zero undrained strengths c and coefficients K pc Calculation procedure Frew executes the following calculation procedure This includes for a profile of pore pressures if specified as indicated 1 Calculation of the total vertical stress 2 Calculation of the effective vertical stress where OO ed 3 Checks to make sure that 0 2 The program stops and provides an error message if this is not so 4 Calculation of the minimum active effective stress oc K0 5 Checks to make sure that 2 0 i e gt If the value is less than zero then the program resets to 0 So generally o K 0 u K c2 0 Gp Kooy NS E ages Ga Kooy
21. Tests FREWman sfd 4 C Program Files Sare3 sFd Exit The user is then prompted to choose the required Gwa file Upon selection the data is transferred from the Gwa file to Safe file Oasys Lid 2014 Frew Oasys GEO Suite for Windows Import GWA Look in FRE ho 2 Bh 4 2 4 2 1 Documents Documents vikram gadicherl a on a File name FREwman qwa Open Network Files of type Text Tab delimited txt v Data Conversion As mentioned before this feature enables the user to create the equivalent Safe model from Frew model There are some approximations and limitations in this data conversion from Frew to Safe The following topics detail the assumptions limitations and approximations involved in this process otages Runs Geometry Hestraints Surcharges Struts Materials Groundwater Unsupported Features Stages Runs otages in Frew are roughly equivalent to Runs in Safe All stages in a Frew model translate to a sequence of runs following each other in Safe without any branching Frew Stages Oasys Ltd 2014 Frew Safe Link T FrewSample fwd Stage Operations Stage Initial Condition Ma change Stage 1 Dewater AHS amp dig to 27 6 mUD Stage 2 Stress anchor Change this stage Stage 3 Lock anchor and dig to 24 6 Stage 4 Install floor slabs and remove anc Delete stage Add stage
22. Tokyo Japan Vol 12 No 1 Pappin J W Simpson B Felton P J and Raison C 1985 Numerical analysis of flexible retaining walls Proc NUMETA 85 University College Swansea pp 789 802 Oasys Ltd 2014 Frew Oasys GEO Suite for Windows 10 10 1 10 2 Pappin J W Simpson B Felton P J and Raison C 1986 Numerical analysis of flexible retaining walls Symposium on computer applications in geotechnical engineering The Midland Geotechnical Society April Poulos 1971 Behavour of laterally loaded piles Single piles Proc ASCE JSMFE 97 5 711 731 Seed H and Idriss 1970 Soil Moduli and Damping Factors for Dynamic Response Analyses Report no 70 10 University of California California Simpson B 1994 Discussion Session 4b 10th ECSMFE Florence 1991 Vol 4 pp1365 1366 St John H D 1975 Field and theoretical studies of the behaviour of ground around deep excavations in London Clay PhD Thesis University of Cambridge Vaziri H Simpson B Pappin J W and Simpson L 1982 Integrated forms of Mindlin s equations G otechnique 22 3 275 278 Wood J H 1973 Earthquake Induced Soil Pressures on Structures PhD Thesis California Institute of Technology Wood J H amp Elms D G 1990 Seismic Design of Bridge Abutments and Retaining Walls Road Research Unit Bulletin 84 Volume 2 RRU Transit New Zealand Wellington Brief Technical Description Suggested Description f
23. 0 0 0 0 0 0 471 6 110 6 10 41 00 41 71 180 0 120 0 83 78 23 78 60 00 0 0 0 0 0 0 0 0 0 0 325 0 188 5 etc Soil Left Right kN 3 0 3 0 3 0 2 0 3 0 3 0 3 0 3 0 3 0 3 0 Oasys Ltd 2014 7 2 1 Stability Check Results The following results are available in the Stability Check results Frew levels fwd Stability Check Results Results of Analysis The required toe level of the wall m 15 08 Ground level active fide m 30 00 Ground level passive side m 4 60 Level Left Right Bending Shear Moment Force Pe u 5011 Soil Pe u m kN m EN m EM m EkN m kNm m EN m 3n nn 00 00 00 0 0 29 00 6 93 00 00 00 1 083 3 464 00 14 15 00 00 9 6053 16 1 27 00 16 62 00 00 00 3712F 42 68 26 00 15 10 00 00 10 21 64 25 00 15 43 205 0 l31 4 24 00 17 99 00 03 362 6 IY 23 00 EL 77 00 00 00 536 5 22 00 25 06 00 00 664 5 37 66 21 00 28 35 00 694 6 35 14 20 00 31 64 00 00 00 5B 19 00 24 94 00 00 254 1 438 15 84 z593 56 56 18 59 41 08 38 08 81 60 EO 15 34 5 oni o 54 1528 15 09 05 s10 04 l 656 3E 6 b53l 3E amp mM D oO 1 1 1 1 1 1 1 2 2 2 2 2 Z 2 The level of each calculation point The separation of
24. 1 270 52 04 97 632 000 2 0 2418 0 2059 0 9075 4690 1 570 52 04 501371 45 5 5 00 zg4 30 0 2418 0 59075 0 4690 1 570 52 04 S247 43 46 r10 00 2 24 20 0 24184 0 2059 0 9075 0 4 90 1 270 52 04 527777 347 10 50 2 0 2418 205595 0 9075 0 49650 1 3570 52 04 5404568 48 11 2 0 2418 O 059 0 9075 0 4 90O 1 270 52 04 552923 11 50 24 20 0 2418 0 9075 0 4690 1 570 52 04 565076 12 00 2 24 20 0 24184 O O59 0 9075 0 4690 1 270 52 04 576974 12 50 2 24 50 0 2414 0 2055 0 59075 0 4690 1 570 52 04 588631 13 00 2 0 24184 0 2059 0 9075 0 4690 1 270 52 04 400062 13 50 2 24 20 0 20553 0 9075 0 4690 1 570 52 04 622273 44 4 2 24 30 0 3414 0 27100 0 0 0 6300 0 0 488045 0 45 15 00 2 z4 30 0 3414 0 2100 0 0 0 6300 0 0 448045 0 Mote Italicized data correpsond to nodes in soil zone influenced by the abutment movement Stresses used calculated in integral bridge analysis Left side Hode Level Material Density ko Pe fat index rest m kN fm 1 kPa kPa kPa l 7 500 1 18 00 4988 z z5 0 1 177 1 418 z 7 000 l 18 00 0 4988 9 000 4 4895 5 671 3 amp 500 l 18 00 0 4988 18 00 8 978 11 35 A nan 1 n 1 2 A 111 These results are printed for each stage below the deflection bending moment shear forces results Notes on Data Entry Whe
25. 3 stages should be defined as usual 2 user should only define one stage as the integral bridge analysis stage and this should be the last stage This is to be defined by the user at the end of all non integral bridge stages 3 The integral bridge stage can be added in the same way as the normal stage However to specify a particular stage as integral bridge analysis stage the user should open the Analysis Options dialog for a particular stage and check the Perform Integral bridge calculations check box Frew 19 1 IntBridgeTest2 fwd Edit View Globaldata Stage data Analysis Tools Window Y 9 2 t Eb We FM arx 5 Input LOL 2 IntBridgeTest2 fwd Analysis data T 12 IntBridgeTest2 fwd Stage Operations 1 m x Units Analysis method Ba Global Stage D Initial condition No che SAFE CO Mindlin LE Material properties 3 stage 1 wall and excavate 3 metres Node levels Stage 2 final stage prop at 0 Iwl Change th Wall soil interface Strut properties 1 Apply remove surcharges 9 Free Fixed C Surcharges v Insert remove struts Partial factors Soil zones 0 Node generation data Water data Wall relaxation 76 o Y Data for Stage 2 Vall data Apply remove surcharges Analysis method Delete Mes Insert remove struts Convergence control Delete Global Poisson s ratio
26. 32 33 34 37 41 52 global softening 71 Graphical Output 3 109 Graphics Toolbar 3 Groundwater 74 87 Hydrostatic 62 Piezometric 62 Inserting Stages 53 Iterations Number of 73 K KO 85 L Lever arm 82 linear elasttic 83 Material Properties 34 52 Materials 83 Mesh 81 Mindlin method Accuracy of 124 Application in 123 Basic model 13 67 123 Mohr Coulumb 83 N New Stages 51 52 Nodes 1 11 24 37 56 60 107 113 P Partial Factors 47 Passive earth pressure 34 135 Limits 11 126 128 132 Oasys Ltd 2014 Output 34 109 Pressures 15 34 Surcharges 45 Passive earth pressure Surcharges 135 Passive softening 71 passive softening depth 71 Poisson s ratio 83 pore pressure 87 Pressure 73 PressureTolerance of 73 Radius of influence 87 Redistribution 15 69 126 Relaxation 24 60 68 149 Restraints 81 Results 33 101 107 108 109 160 Rigid boundary 67 Runs 79 5 SAFE method 1 12 68 113 Accuracy of 13 Approximations 113 Fixed or free 68 Save Metafile 109 Scale Engineering 109 Shear Force 1 107 109 Soil strength factors 47 Soil Zones 56 Stage Changing titles 53 54 Construction 1 Data 51 Deleting 53 Editing 52 Stage 0 11 19 24 52 otages 79 Standard Toolbar 3 otrp Loads 44 45 135 Active pressures 133 Passive pressures 135 Struts 82 Levels 37 Frew Oasys GEO Suite for Windows Struts 82 7 Properties 1 41
27. Amend the level of the node and select OK 2 As an alternative go to the table at the side of the diagram Use the arrow keys and return button or the mouse to select the appropriate node Change the value and press enter Deleting nodes Nodes can be deleted by 1 Placing the cursor over the correct node and then using the left mouse button whilst simultaneously holding down the Shift key 2 Highlighting the line number in the table using the left mouse button then pressing the Delete key 3 4 5 Strut Properties otruts may be inserted or removed at any node at any stage in the analysis All the struts required for the various stages of analysis however must be inserted in the global data Struts and anchors are modelled in terms of an equivalent strut which represents the total number of struts present in a one m length of wall e g for struts at 2m centres input half the force and stiffness of an individual one strut spacing per length of wall For each equivalent strut the following items are required Oasys Ltd 2014 input a2 FREWman fwd Struts jeg Ee 9 Jn Strut Stage Hode Prestress Stiffness Angle Lever arm ru In Out number m m b Defaults i 2 200 00 0 00 40 00 0 50 b 2 0 00 2000 00 40 00 0 50 11 1 0 00 40000 00 0 00 0 00 10 0 00 40000 00 0 00 0 00 1 0 00 20000 00 0 00 0 00 0 1 0 00 20000 00 0 00
28. Drained Materials Rc 19 2 5 2 Undrained Materials and Calculated Pressures 19 2 5 3 Undrained Materials and User defined Pressure 7 4 21 2 9 4 Undrained to Dr ained Example ai asset Um 23 3 Input Data 23 cs ASSOMDINNG Dala 24 3 22 CCELI EET 29 3 3 New Modei Wi ard TEN 30 3 3 1 New Model Wizard Titles and Units 30 3 3 2 New Model Wizard Basic Data 30 3 3 3 New Model Wizard Stage Defaults 404 22 406 x LUE UR REC ennan EK 31 3 4 D la sagen usu ea bore RN EM D ELE 32 SN M EET NN T eT 32 Sac Mies window Feria i oS Hide RN 33 342 Uns
29. E Me Wal nil to left E Soil to right m E NA The stiffness is computed as K EA L where Young s modulus of the soil A distance between the mid point of the elements immediately above and below the node under consideration Oasys Ltd 2014 15 Frew Oasys GEO Suite for Windows 2 4 L spring length input by the user It is considered that this model is not realistic for most retaining walls and no assistance can be given here for the choice of spring length which affects the spring stiffness Note The sub grade reaction model is not currently active it will be added to Frew in the near future Active and Passive Pressures The active and passive pressures are calculated from the following equations Note The brackets indicate the active pressure is only applied when the active force from the surface to level z is positive Otherwise the pressure is set to zero pa ka o v kac c u kp O v kpe c Where pa and pp active and passive pressures ka and kp coefficients of active and passive pressure kac Kpc coefficients of active and passive pressure effective cohesion or undrained shear strength as appropriate prescribed pore pressure with soil cohesion these are generally set to Ko 24 Ki E 2 IK Where Cw cohesion between wall and soil O v vertical effective stre
30. Equivalent Fluid Pressure Oasys Ltd 2014 Input Data 2 rREWman fwd Stage Operations Convergence control Stage b Excavate to Final Level 40 5 1 Apply remove surcharges Inisert remoeve struts af zones af Water data Wall data Analysis methad Convergence control ll equivalent fluid pressure Stage b Apply Roof amp Basement Slab Add stage 7 Undrained to Drained PP Mew stage will be added Apply remove surcharges after the current stage as shown an the Status bar Delete stage Selecting the Minimum equivalent fluid pressure option the MEFP parameters table appears FREWman fwd MEFP Parameters Siz Ny Left Right im MER im me Glacia Defaults d SaL 50 00 0 00 S 40 00 0 00 3L 36 00 0 00 SL 36 00 0 00 5 00 50 00 0 00 50 00 0 00 se gt This table has a record for each material with parameters for left and right sides The required MEFP is specified as a linear relationship with depth plus an optional constant value a gradient of pressure default 5 yg level default is top level of material b constant value default O Note The user should really set the values to zero where they judge they are not needed or would Oasys Ltd 2014 Frew Oasys GEO Suite for Windows incorrectly affect the re
31. Ky Ky KasJZx x 1 For which x denotes each node o is the effective stress at the mid point of the element above v xt o IS the effective stress at the mid point of the element below is the combined static and dynamic earth pressure coefficient for relevant soil layer k is the active earth pressure for the soil at node x and z is the distance from the mid point of the element above to the mid point of the element below To calculate the value of the combined pressure coefficient first the value of is calculated as shown below for unsaturated soils tan kpn for saturated impervious soils tan Ys Yw 1 ky for saturated pervious soils Ya tan Ys Yw 1 Ky The combined earth pressure coefficient K can then be calculated based on the formulae shown below ifB lt sO 9 K sin Y 0 cos 2 sinQy 0 a 1 M orif gt 0 Oasys Ltd 2014 9 Frew Oasys GEO Suite for Windows sin Y 0 cos 21 sin 64 For which is the design shear angle of the soil is the angle of friction on the soil wall interface and the directions of the forces acting on the wedge and geometry of the wedge are as shown in the following diagram The active earth pressure coefficient is calculated as described in Calculation of Earth Pressure Coefficients In additio
32. Oasys Ltd 2014 23 Frew Oasys GEO Suite for Windows Note Frew uses as a lower limit on the horizontal effective stress B is used in the equilibrium equations for determination of the wall deflection where Effect of specified pore pressure opecified pore pressure u takes effect in steps 2 and 5 otep 2 Specified pore water pressure reduces the effective vertical stress Step 5 Limits the apparent horizontal effective stresses to gt 0 In earlier versions of Frew this could be used to advantage because the specified pore pressure u could become equivalent to a minimum fluid pressure There is now a completely separate feature in which a minimum equivalent fluid pressure MEFP can be specified see Minimum Equivalent Fluid Pressure 2 5 4 Undrained to Drained Example An example file Undr PP Example fwd is available in the Samples sub folder of the program installation folder The user can see from this the way that the feature for automatic calculation of undrained pore pressures has been used 3 Input Data Data is input via the Global Data and Stage Data menus or via the Gateway Some basic and global data can be input to a new file using the New Model Wizard but the following gives some background on the way the data is organised and can be edited after initial entry Global Data File Edit View MeESREEN Stage data Analysis Graphics Window Help Units and Preferences v Titles
33. Pressures The values of active and passive pressures due to strip loads parallel to the wall are discussed in Active Pressures due to Strip Load Surcharges and Passive Pressures due to Strip Load Surcharges The method described for the active pressure is automatically applied by the program but the method described for the passive pressure is not applied Ihe user must therefore manually enhance the passive pressure coefficient or the soil cohesion c if this effect is to be incorporated into the analysis see Passive Pressures due to Strip Load Surcharges The user is recommended to study the graphical output and check whether the pressures adopted by the program are acceptable 3 4 7 Partial Factors The purpose of factors is to allow for uncertainty in material properties loading and calculation models and to ensure safety and acceptable performance These are global factors that are applied to material properties or surcharges input parameters The new material parameters affected by these factors will then be used in the calculations A single set of factors shall be selected and these will apply to all materials in all stages WARNING Frew has had new features added to simplify application of partial factors in line with EC7 However there are alternative ways of complying with EC7 including manual adjustment of certain values The features in the program do not automatically make a design EC7 compliant and the user must cont
34. Therefore P W qB JK Oasys Ltd 2014 137 Frew Oasys GEO Suite for Windows 8 5 2 2 Requirement 2 Check of the depth of influence of the load Zz Zw 25 E a X Approximate pattern of af influence a critical wedges Calculation The effect of the surcharge q will not be felt above T fade 4 2 A V K This depth will be smaller in the presence of wall friction In this case it is probably reasonable to use the same formula with a larger value of Kp Note Extra passive force may not be fully applied by depth d B cot 45 5 _ A B K 8 5 2 3 Requirement 3 For a uniform surcharge A 0 and B Oasys Ltd 2014 Detailed Processes in Frew 138 The pressure due to the uniform load P d E qK It is unlikely that passive pressure increase for a strip load exceeds value for uniform surcharge i e Note The required total force P due to a uniform load A A B K 4 8 5 2 4 Requirement 4 General Application To be safe the effect of passive pressures should be placed rather low Therefore the stress block shown below is considered to be generally suitable The pressure can be expressed by the following equations Calculation Oasys Lid 2014 Frew Oasys GEO Suite for Windows 8 6 8 6 1 E 4 gt qh z 2 J Depth criteri
35. and Passive Limits 8 Active earth pressure Axi symmetric problems 142 Limits 11 12 126 128 132 Output 109 Pressures 15 34 127 Surcharges 45 133 Surcharges 133 Tolerance 73 Analysis Methods of 1 Procedure 11 Anchors 43 141 Angle of friction 83 Assembling data 24 Axis Graphical output Axi symmetric Proble B Backfill 109 ms 142 145 Effects of 16 24 Modelling of 59 Batch plotting 112 Bending moments berm 145 berms 145 Bitmaps In titles window Boundary 67 Distances 67 11 33 Horizontal rigid 37 67 Vertical 67 118 boundary distances C 67 74 Components of the User Interface Convergence Control 72 Copy graphics 109 Creep 149 Damping coefficient 73 Data Checking 101 Data Entry 74 Deflection Calculation 139 Graphical representation 109 Direct Kp factors 47 Displacement Maximum incremental 74 Tolerance of 73 Drained materials 16 18 19 21 24 34 44 52 152 E Earth pressure at rest 18 34 Effective stress 18 element edge loads 82 Example Analysis procedure 11 12 13 Manual 24 Excavation Effects of 16 37 45 123 Modelling of 59 142 Export 74 Factors of safety 47 File New FREW file 24 first stage material 85 Fixed and Free solution 68 122 Fixed Earth Mechanisms 4 Fixed or Free solution 68 Free Earth Mechanisms 5 Frew Toolbar 3 G Oasys Ltd 2014 Gateway 3 Geometry 81 Global Data 24
36. are required to specify the convergence criteria for the calculations Note These parameters can be changed for each stage Oasys Lid 2014 Frew Oasys GEO Suite for Windows 2 FREWman fwd Convergence control 3 5 13 1 3 5 13 2 3 5 13 3 3 5 13 4 number af iterations Tolerance for displacement convergence mm Tolerance for pressure convergence rr Damping coefficient I aximum incremental displacement m Apply Convergence control parameters may be varied from the default values offered to improve the speed accuracy of the solution or to reduce the chance of numerical instability Maximum number of Iterations The maximum number of iterations for each stage can be specified The stage calculations will complete at this maximum number of iterations if this is reached before both the tolerance criteria given for the displacement and pressure are satisfied If the tolerance levels are reached first then the stage calculations will also complete Note The default value for the maximum number of iterations is given as 900 Tolerance for Displacement The maximum change of displacement between successive iterations The absolute error in the result will be considerably larger typically by a factor of 10 to 100 The default value is 0 01mm Tolerance for Pressure The maximum error in pressure i e how much the pressure at any node is below the active limit or in excess of the p
37. be deleted when results are deleted Note To analyse intermediate construction stages it is necessary to create additional files for each stage that you wish to analyse These files should be created as above but with the final stage being that for which the seismic analysis is required and with all subsequent stages deleted Oasys Ltd 2014 Seismic Analysis 6 2 Seismic Analysis Methods When analysing the forces generated by seismic ground movement forces attributable the soil movement need to be considered and potentially forces generated by the groundwater where some or all of the retained soil is saturated and it is highly pervious to movement of the groundwater There are two principle methods in Frew to calculate the dynamic soil force Mononobe Okabe and Wood s method The calculations undertaken by Frew to generate soil forces based on these methods are outlined in the sections Calculation of Seismic Coefficients Wood s Method Mononobe Okabe Method and Load Application Methods The calculations to determine the dynamic load from groundwater are covered in the section Groundwater Loading 6 2 1 Calculation of Seismic Soil Pressure Coefficient Horizontal Seismic Coefficient Kh Where the calculated Kh option is chosen Kh will be calculated using the following formula Kh S r For which e is the ratio of the design ground acceleration to acceleration due to gravity e S is the soil factor specified by the us
38. cantilever situation where the fixed method will give less displacements because it models greater fixity between the soil and wall It must be noted that the case with interface friction fixed is somewhat approximate because Poisson s ratio effects are not well modelled For example these effects in a complete elastic solution can cause outward movement of the wall when there is a shallow soil excavation For detailed information on the approximations and thereby the accuracy of the Safe method see Approximations used in the Safe Method 2 3 2 Mindlin Method The Mindlin method represents the soil as an elastic continuum modelled by integrated forms of Mindlin s elasticity equations Vaziri et al 1982 The advantage of this method is that a wall of finite length in the third horizontal dimension may be approximately modelled lt also assumes that the soil wall interface has no friction Oasys Ltd 2014 Methods of Analysis Horizontal dimension Accuracy of the Mindlin Solution The method is only strictly accurate for a soil with a constant Young s modulus Approximations are adopted for variable modulus with depth and as with the Safe method the user can override this by setting a constant modulus value For further information see Approximations used in the Mindlin method 2 3 3 Method of Sub grade Reaction The soil may be represented by a Sub grade Reaction model consisting of non interacting springs
39. must have zero water pressure Negative pore pressures can be specified below the highest point to describe soil suction The water pressure is assumed to increase hydrostatically below the lowest specified point The water pressures are also assumed to be constant laterally from either side of the wall Adding piezometers Piezometer data is entered by selecting the piezometer button t on the graphics toolbar or the in the Stage Operations window Water data on the left or right side of the wall can be viewed by selecting the appropriate page tab at the bottom of the table Oasys Ltd 2014 Frew Oasys GEO Suite for Windows Seles gt s M ni 2 ni bal Current selection Nodes 10 KM rn ad L 4 4 0 ee 4 4 Scale x 1 254 y 1 328 STAGE 7 Undrained to Drained FUP Adjustment Oasys Ltd 2014 Input Data FREWman fwd Water data A B Level Pressure Unit weight Piezo Zm kN mi Defaults 47 00 0 00 10 00 46 00 27 45 45 00 34 95 44 00 29 50 43 00 24 05 42 00 15 65 41 00 13 20 40 00 39 00 4 90 39 00 90 00 4 gt XLeft Right A piezometric groundwater profile can be entered in the table or by placing the cursor at
40. o 7 2 90 110 55 1 2 5 2 234 252 270 268 306 342 Tatal Total DEL Del Pe Dele MEN NENNEN mM LS GENES ANN 144 162 180 215 234 282 BE NH NI L 342 T atal B4 82 11 142 100 12 118 13 136 14 154 15 172 1B 190 L 1997 704 904 1 deri 1 1 tm cm cm oa E eur 74 00 en 1 liani lo c3 ca c9 17 208 18 22B 18 244 20 262 53 90 Im D E m Cl Oasys Ltd 2014 Detailed Processes in Frew 55 Calculated u Against Level 140 120 100 80 60 40 20 PWP kPa 90 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 Level mOD Graphical Results Last Undrained Stage Displacement 50 29 25 50 75 55 50 45 zL 5 En 1 L P Fl zz L 40 35 30375 260 125 D 125 25D 375 Pressure kPa Scale 1 300 STAGE 7 Insert strut dig ta 42 5m OD Stage A Adjusted PWP Oasys Ltd 2014 157 Frew Oasys GEO Suite for Windows Displacement mm 18 50 29 25 50 75 55 2 i 50 See 45 7 a 40 35 425 T 125 250 375 Pressure kPa 30375 250 Scale 1 300 STAGE 3 Mew PWP Profi
41. prestress stiffness inclination and a lever arm to represent rotational fixity surcharges including depth and extent e groundwater levels and pore pressures each side of wall The program gives results for earth pressures shear forces and bending moments in the wall strut forces and displacements These are presented in tabular form and can be plotted diagrammatically In addition the number of iterations the displacement error between successive interactions and the maximum earth pressure error are output Full details of the assumptions and analysis methods are included in the following paper Pappin J W Simpson B Felton P J and Raison C 1986 Numerical analysis of flexible retaining walls Symposium on computer applications in geotechnical engineering The Midland Geotechnical Society April 11 Manual Example 11 1 General The data input and results for the manual example are available to view Frew data file format or pdf format in the Samples sub folder of the program installation folder The example has been created to show the data input for all aspects of the program and does not seek to any indication of engineering advice Screen captures from this example have also been used throughout this document This example can be used by new users to practise data entry and get used to the details of the program Oasys Ltd 2014 Frew Oasys GEO Suite for Windows Index A Active
42. short term has been stressed to Point A In the course of time its state will move to be somewhere on line BC lf it is in a situation in which there is no change of strain during this change stresses will simply relax and it will move to point B If on the other hand the load on the element can not change it will creep and move to point C Thus relaxation and creep are different manifestations of the same phenomenon It is easier to think about the working of Frew in terms of relaxation than of creep In Frew if an element is at point A and the only change made is to change the Young s modulus in the data further behaviour will proceed along line AD This does not represent creep or relaxation Somehow the program must be informed that even if nothing moves stresses will change from point A to point B If these new stresses are no longer in equilibrium the program will then respond by further strains and the stress state will move up line BC Creep effects on bending stiffness El in Frew can be modelled directly by using wall relaxation Relaxation calculation The relaxation percentage is defined as 100 For example for a concrete the short term and long term stiffness are taken as 30 and 20GPa respectively The relaxation percentage would be 30 20 30 100 33 396 At the same time the value of wall stiffness will be reduced to 20GPa Supporting struts and slabs Creep in supporting struts or slabs can also b
43. specifying for an undrained material another material zone from which effective stress parameters are to be taken A shape factor is also required which controls the shape of the permitted effective stress path for undrained behaviour default value for the shape factor is 1 which prevents occurrence of any effective stress state outside the Mohr Coulomb failure envelope but it can optionally be revised to 0 representing a Modified Cam Clay envelope or any value in between NB values less than 1 have not been validated and use of a value less than 1 is not recommended The option is retained in the program for experimental purposes spreadsheet undr dr calc xls is provided in the Samples sub folder of the program installation folder This allows the user to experiment with values for the various parameters and with the shape factor if wished If reasonable values of pore pressure are not used during undrained behaviour then on transition to drained behaviour the program may not calculate displacements with satisfactory accuracy The calculation in Frew aims to provide a reasonable set of undrained pore pressures Given the relative simplicity of Frew and the present state of knowledge of soil behaviour they cannot be accurate although should be better than a user defined pore pressure profile and the user should check that they appear reasonable Guidance on warning messages is given below The process used in the program ca
44. stiffness can be changed or relaxed at the various stages of the analysis e Soil profiles are represented by a series of horizontal soil strata that may be different each side of the wall The boundaries of soil strata are always located midway between node levels This constraint will be accommodated when using the Automatic Node Generation feature e Struts may be inserted and subsequently removed Each strut acts at a node If the Automatic Node Generation feature is used a node will be generated at each specified strut level A strut may have a specified stiffness pre stress and lever arm and may be inclined to the horizontal For inclined struts with a non zero lever arm a rotational stiffness at the node is modelled Surcharges may be inserted and subsequently removed Each surcharge comprises uniformly distributed load or a pressure load of a specified width e Soil may be excavated backfilled or changed at each stage on either side of the wall e Water pressures may be either hydrostatic or piezometric e The program provides a selection of stiffness models to represent the soil 1 Safe flexibility model 2 Mindlin model 3 Sub grade reaction model Note The sub grade reaction model is currently not active it will be added to Frew in the near future e All methods allow rigid vertical boundaries at specified distances from the wall A rigid base is also assumed at the lowest node for the Safe and Mindlin me
45. t Soil zones Add st Water data TUER Wall plan length m Left 1 New stage will F ght 1 piii igi Redistribute pressures Mir Analysis method 7 i n Convergence control Perform integral bridge calculations G Output Tabular output Passive Softening This would cause more items to be available in the Gateway These new items are Integral bridge data Kp vs D H curves and Rf g vs D H curves The user should enter the necessary data in these dialogs and tables Oasys Ltd 2014 Integral Bridge Analysis 33 Integral Bridge Manual Test mixed granular cohesive 1 fwd Integral bridge analysis data In front of wall d behind wall i mm H at front of wall m amp Data for Stage 3 d at front of wall gt Apply remove surcharges Insert remove struts Convergence data Soil zones Tolerance on d H Water data Maximum number of iterations Strut data Index of strut modelling thermal expansion contraction 2 Material parameters x Soil IBN IE CT ETE Defaults 00 pepe K vs d H vs 1 StandaPdEN EP 22 00 90 Standard EN 6P 541 90 Densifi SLE eii LLL 1 51 90 Densification Add Curve mp xc vs D H 4500 pp
46. the active passive limit If redistribution is specified this correction will be a function of the pressures mobilised at nodes above node i i e lt i 2 For node i calculate approximately the displacement correction DCII i that would cause the force at i to change by FORCOR DCII i FORCOR S Ll Where 5 is the diagonal term of the soil stiffness matrix corresponding to node i 3 For nodes j j i calculate the displacement correction DCJI i j that is required to prevent change of pressure at when the displacement at i is corrected by DCII i 4 Repeat 1 to 3 for all nodes i 5 For all nodes i calculate the total displacement correction Oasys Ltd 2014 133 Frew Oasys GEO Suite for Windows 8 5 8 5 1 DCTOT i DCI i 6 Calculate the elastic soil force corrections from DCTOT x soil stiffness matrix add these to the initial forces and recalculate the displacements DISP using the overall elastic system the sum of the wall strut and soil stiffness The soil forces F acting at the nodes can then be recalculated as 5 x DISP DCTOT 7 Repeat 1 6 iteratively to obtain convergence of DCTOT Active Pressures Due to Strip Load Surcharges Considerable efforts have been made to formulate a relatively simple approximation to model the effect of a strip load on the active pressure limits Parametric studies were carried out using straight line and log spiral shape
47. the wall will be as manually specified by the user or as generated by the stability check as required For manual node generation the wall bending stiffness El value in KN m2 m length of wall is specified at each node location This allows the stiffness to be varied throughout the length of the wall The stiffness given to each node applies from that node down to the next node The base of the wall is taken as the first node with a given El value of zero Adding wall stiffness when using manual node generation To add wall stiffness profile select the wall stiffness button on the graphics toolbar the Wall data option in the Stage Operations window Oasys Ltd 2014 Frew Oasys GEO Suite for Windows EIE A s s adap FREWman fwd Data Entry View Curent selection Modes FREWman fwd Node Data Level EE Left m m material material Defaut kiim Scale x 1 240 w 1 335 STAGES Excavate to Final Level 40 5m00 amp OQewater Wall stiffness can either be entered directly into the table or graphically using the procedure given below Select the required range of nodes on the wall N Hold down the Shift key 3 Place the cursor over the last node still holding down the Shift key and select the area of nodes with the left button To designate the wall stiffness 1 Place the cursor to the left or right
48. vertical effective stress due to wall friction should be made by taking appropriate values of k and K and K horizontal coefficients of active and passive pressure and cohesive coefficients of active and passive pressure can be evaluated as s x 24 3 c iem 2 M u Where wall adhesion Note For conditions of total stress K 1 Oasys Ltd 2014 9 Frew Oasys GEO Suite for Windows For a given depth z 2 oy y dz 6 ud uU where Ys unit weight of soil pore water pressure vertical sum of pressures of all uniformly distributed loads udl s above depth z A minimum value of zero is assumed for the value of kK Cc Effect of strip surcharges The effect on the active pressure of strip surcharges is calculated by the method of Pappin et al 1986 also reported in Institution of Structural Engineers 1986 The approximation which has been derived is shown below Width Ofset B t Line af Wall At 1 a Total area equal to tle 1 8 4 u Output p increment B p 5 Approximation to represent Approximation of active the change in active pressure pressure by equivalent due to a strip surcharge forces used in STAAL Oasys Ltd 2014 Methods of Analysis to Note If the width of the load B is small the diagram will b
49. 0 00 0 00 0 00 20000 00 0 00 0 00 0 00 20000 00 0 00 0 00 1 5 1 2 2 1 0 00 40000 00 0 00 0 00 0 1 0 Oasys Ltd 2014 Input Data 3 5 9 Soil Zones The layers of soil on either side of the wall are described in terms of Soil Zones They are added by tabular or graphical input and are shown graphically in the general display of the layout of the wall Note The interfaces between the soil zones are set midway between nodes If automatic node generation is being used the program will do this for you Otherwise the locations of soil zone interfaces must be taken into account when defining the node positions To add soil zones select the soil zones button on the graphics toolbar or the soil zones option from the relevant stage in the Stage Operations window Adding editing soil zones when using automatic node generation To add a soil zone Left click on the graphical input view at the required level of the soil zone interface and choose the required material from the dropdown list in the dialog which appears Soil Zones Maternal for new 011 zone Material 3 E Cancel Click OK and the graphical input will be redrawn with the new soil zone shown Alternatively the data can be added to the Material Layers table which will open at the same time as the Graphical Input view for this option Frew1 Material layers Jota __ A Layer EE Material Defaults Hone
50. 139 141 Sub grade Reaction 14 67 118 Surcharge factors 47 Zoom Facility 109 Surcharges 44 82 Strip loads 15 44 135 Strip loads 133 Uniformally distributed loads 18 44 45 T Table View Tabular Output 3 Tabulated Output 104 Titles 32 54 Toolbar 3 U Uniformally distributed loads 44 45 Units Unsupported features 88 User defined factors 47 User Interface 3 V validation 74 void 83 W Wall 1 83 Data 11 60 Deflection 109 Friction 13 15 122 Geometry 1 24 60 Relaxation 24 60 68 Stiffness 1 37 41 43 44 45 51 52 53 54 55 56 60 139 Stiffness 52 wall data 74 Wall Friction 122 Y Youngs modulus 68 Oasys Ltd 2014 Endnotes 2 after index Oasys Ltd 2014
51. 15 Groundwater Distributed load Point load at height f H from base 0 22323 Apply d 4 Now select the preferred analysis method and method for load application If you intend to use calculated Kh values it is also necessary to input the S value and specify the design ground acceleration and acceleration due to gravity Once the required data has been input click on Apply Oasys Ltd 2014 Frew Oasys GEO Suite for Windows Note The analysis type and load application methods are described in more detail in the Seismic Analysis Methods section Calculated Kh values are determined using the methodology described in Eurocode 8 see Calculation of Seismic Coefficients the S values for a range of stratigraphy types are given in Eurocode 8 Part 1 5 Having chosen to perform seismic analysis the Seismic material parameters option becomes visible for the final stage in the gateway and stage tree dialog Click on either of these to open the seismic material parameters table and then input relevant parameters as described below Note that there is one entry in this table corresponding to each of the materials in the general material parameters table Parameter Description This a non editable field and gives the material description as per the main Description material parameters table Dry unit weight Dry unit weight of the soil for calculation of lateral earth pressure Saturated unit weight Saturat
52. 39 00 38 00 37 00 36 00 35 00 34 00 33 00 32 00 31 00 30 00 29 00 29 00 0 00 Erg 10 Sr 1 500000 10 50000010 50000010 50000010 50000010 50000010 50000010 50000010 500000 10 50000010 50000010 500000 10 50000010 50000010 50000010 50000010 0 00 0 00 0 00 0 00 0 00 Mone Glacial Till Undrained Glacial Till Glacial Till Undrained Glacial Till Undrained Glacial Till Uridrained Glacial Till Undrained Glacial Till Glacial Till Undrained Glacial Till Undrained Glacial Till Glacial Till Undrained Glacial Till Undrained Fluviaglacial Sands Fluviaglacial Sands Fluyioglacial Sands Fluviaglacial Sands Fluvioglacial Sands Fluyioglacial Sands Fluvioglacial Sands Fluyvioglacial Sands Fluviaglacial Sands Fluviaglacial Sands Fluvioglacial Sands from the list presented in the drop down box Glacial Till Undrained None Glacial Till Undrained Fluvioglacial Sands Glacial Till Dirained Alternatively soil zone data can be entered graphically using the procedure described below Select the required range of nodes on the wall Mone None None Mone Glacial Till Undrained Glacial Till Undrained Glacial Till Undrained Glacial Till Undrained Fluyioglacial Sands Fluvioglacial Sands Fluvioglacial Sands Fluyioglacial Sands F
53. 72 Kh2 Layer 3 73 Kh3 Layer 4 74 Kh4 Layer 5 75 Kh5 Mononobe Okabe Method The Mononobe Okabe method is based on a classic coulomb wedge analysis but with an enlarged active wedge taking account of the additional horizontal ground acceleration resulting in a change in the direction of the principle stress The method was first proposed in Okabe 1926 and Mononobe amp Matsuo 1929 and has been developed since The method detailed below and used in Frew is derived from BS EN 1998 5 2004 Annex E Using this method the total force acting on the retaining wall Ed can be given by 1 7 E sv F k KH Ewa For which K is the combined static and dynamic earth pressure coefficient the soil unit weight Kv the vertical seismic coefficient H the retained soil height Ews the static water force and Ewd the dynamic water force Given that the strut force should only represent the additional dynamic loading from the soil APd and not the total load applied to the wall the previous formula can be amended to give Oasys Ltd 2014 Seismic Analysis 1 2246 t k K kq H or for cases where Kv 0 1 Y The calculations in Frew are based on this evaluating the additional force for each node along the face of the wall then taking the sum of these to determine the total additional seismic force This can be written as 1 APg gt 2 Oyxp 1
54. Ae S e i EN Tm 107 7 2 2 1 Results Annotations and Error 108 roc E Graphical ge pt 109 TA Baten PIOUING 112 8 Detailed Processes Frew 113 B ecu iu d Ii IM LEM EI M IEEE 113 8 2 Approximations Used in the Safe Method 113 82 I The BASIC SATE NOC N TETTE 113 8 2 2 Application of the Model in Frew 114 8 2 3 Accuracy with Respect to Young s Modulus E 116 8 2 3 1 Linear Profile of E With Non Zero Value at the 116 9222 OF dont oen o ded a cu eae oat alfo naan 116 8 2 4 Effect of the Distance to Vertical Rigid Boundaries 420 211 1 0 2 1 0 20141 41 2 444884 8 000142411 nenne 400000004044 118 8 2 4 1 Accuracy of Modelling Boundaries in etel ad d vd dd 119 8 2 5 Friction at the Soil Wall Interface 1 eere rennen nnnm nnnm 122 8 2 5 3 Accuracy olihe Fixed seda dut dove teda o
55. Apply Anchor Prestress Stage 4 Apply Anchor Stiffness Stage 5 Excavate to Final Level 40 5m0 Stage b Apply Root amp Basement Slab Str Stage 7 Undrained to Drained PP Stage B Undrained to Drained Switch 5 Stage 2 Undrained to Drained PMP tac Stage 10 Remove Plant Loading Stage 11 wall amp Strut Relaxation stage will be added after the current stage shown an the Status bar HEIL REI PEL PREIS REI RET RET RET RET REI Note Left click on the boxes and E to open or close the tree diagram for each stage As mentioned earlier the user can access stage specific data of the current stage using the Gateway Note Oasys Ltd 2014 Input Data 52 3 5 1 Stage 0 Initial Conditions The information must first be set for Stage 0 the initial conditions before entry of the wall in Stage 1 Stage 0 appears automatically in the summary tree diagram on creating a new file The individual data for each stage can be accessed by using the mouse double left click on the data heading in the tree diagram This action opens the window for data input The following data must be entered to allow the calculation of stage 0 Global Data Stage 0 Data Compulsory Material properties Soil zones drained materials Node levels Surcharges Analysis Method Struts Convergence control parameters Optional Water data Note The properties set in Stage will be carried forward into subsequent s
56. Disp Node Press Node no max no error no error no displ mm mm kN m 1 0 0 1 5 1375 1 0 14 11 Oasys Ltd 2014 Frew Oasys GEO Suite for Windows 2 6 3 6 4 6 5 6 10 6 15 Tis 20 Ja 23 ue Ground level left 50 00 N ND oO W EF PE OO 1587 1620 1570 0971 0484 01867 0092 OB 9 1 lt 65 01 00 71 KD 26 e e oO du C H Ground level right 40 50 Stress Pore Stress Pore Node Level Disp Vt Ve Pt Pe Pressure Vt Ve Pt Pe Pressure BM Shear m mn kN m kN m kN m kN m kN m m kN m kN m kN m kN m kNm m kN m 1 50 00 36 93 5 000 5 000 1 026 1 026 0 0 0 0 0 0 0 0 OO 0 0 uua 0 0 50 00 0 0 144 5 2 49 00 42 05 20 00 20 00 29 42 29 42 0 0 0 0 0 0 0 0 0 0 0 0 144 0 129 3 3 48 00 44 89 40 00 40 00 8 080 8 080 0 0 0 0 0 0 0 0 0 0 0 0 Zo ged edd 4 47 00 47 21 58 75 Hee TS 11 67 11 67 0 0 0 0 0 0 0 0 0 0 0 0 6253522 99 97 5 46 00 48 81 80 00 70 00 24 12 14 12 10 00 0 0 0 0 0 0 0 0 0 0 458 6 81 35 6 45 00 49 50 100 0 80 00 36 08 16 08 20 00 0 0 0 0 0 0 0 0 0 0 nete 22003 7 44 00 49 15 120 0 90 00 48 01 I0 30 00 0 0 0 0 0 0 0 0 0 0 561 1 9 205 8 43 00 47 69 140 0 100 0 59 92 19 92 40 00 0 0 0 0 0 0 Ou 0 0 546 3 44 76 9 42 00 45 16 160 0 T2 250 dl 29D 269 50 00 0 0 0 0
57. Frew Version 19 2 Oasys Oasys Ltd 13 Fitzroy Street London W1T 4BQ Central Square Forth Street Newcastle Upon Tyne NE1 3PL Telephone 44 0 191 238 7559 Facsimile 44 0 191 238 7555 e mail oasyS arup com Website http www oasys software com O Oasys Ltd 2014 Frew Oasys GEO Suite for Windows Oasys Ltd 2014 All rights reserved No parts of this work may be reproduced in any form or by any means graphic electronic or mechanical including photocopying recording taping or information storage and retrieval systems without the written permission of the publisher Products that are referred to in this document may be either trademarks and or registered trademarks of the respective owners The publisher and the author make no claim to these trademarks While every precaution has been taken in the preparation of this document the publisher and the author assume no responsibility for errors or omissions or for damages resulting from the use of information contained in this document or from the use of programs and source code that may accompany it In no event shall the publisher and the author be liable for any loss of profit or any other commercial damage caused or alleged to have been caused directly or indirectly by this document This document has been created to provide a guide for the use of the software It does not provide engineering advice nor is ita substitute for the use of standard referen
58. H meters E DEPTH imaers Comparison of Safe and Mindlin flexibility approximations wth FEA at three depths It can be seen that Frew provides quite good results when used with the Mindlin equations 8 4 Calculation of Active and Passive Limits and Application of Redistribution This section describes how active and passive limits are defined in Frew The description refers to the requirements of certain parameters and equations being necessary and sufficient denotes a condition which must be met in deriving a conservative solution sufficient denotes a condition which will ensure that a solution is conservative An item of information may therefore be necessary but may also not be sufficient on its own to ensure a conservative solution An ideal accurate solution is both necessary and sufficient Oasys Ltd 2014 127 Frew Oasys GEO Suite for Windows 8 4 1 General Approximations to the limiting pressures on a retaining wall may be calculated using either lower bound or upper bound methods For the lower bound method a set of equilibrium stresses which does not violate the strength of the soil is studied The limits which are calculated by this approach are sufficient for stability ensuring a conservative solution but may be unnecessarily severe Rankine used a lower bound method to calculate active and passive pressures in simple solutions He assumed that wall pressure increased line
59. Ltd 2014 Detailed Processes in Frew 146 passive pressures within the berm can be calculated P y K 2c K o The values of c should be chosen such that the forces transferred through the berm will be big enough to cause any failures type A B or even C The passive resistance of the ground beneath is also affected by the berm At any depth a failure surface type C needs to be examined and a total passive force calculated This passive force includes the horizontal forces transferred into the ground through the berm 8 8 1 Rigorous Method Therefore berms may be treated as follows 1 For elastic and active effects treat as a full layer of soil For passive effects within the berm treat as full layer but use G At the level of the excavation within the berm place a strip load surcharge with negative pressure to remove the weight effect of the berm with properties q y h average width of berm distance to boundary and Kr of soil beneath berm Note that Frew disregards the effect of strip surcharges on limiting passive pressures Therefore this negative pressure does not change the limiting passive resistance of the ground below It will however cause some movement which corresponds to the elastic effect of the excavation within the berm Also note that several surcharges could be used at various levels within the height of the berm This could give a somewhat bet
60. Ra e E d c e 69 251227 Equivalent Fluid ere de t Hasta 69 3 9128 5 71 9 9 72 3 5 13 1 Maximum number of 73 3 5 13 2 Tolerance for 2 mae this Ds ear Uo rw oe d e e 73 3 9 13 3 Tolerance TOF FEOSSUEB del EYE Ces CV ool Ko EE 73 35 134 Pamp NO COST Tele 73 3 5 13 5 Maximum Incremental 74 4 Frew Safe Link 74 1 DAA ENUY t 74 42 Data Conversion ae CD MI ELS DD LN OT LEE 79 AZ Stages 79 424 iustiniano pu ic Een c E EN DIEI 81 A23 Reslas ugt unen i tcc cM eM I M ME 81 42A ici ide arige A E 82 25 nmi M MIDI MEI iy 82 425 Mal rialS 83 4 2 6 1 First Stage Maternal 85
61. The original area can be restored by clicking on the restore zoom icon as shown here Smaller Larger font allows adjustment of the font sizes on the graphical output view Edit colours allows line and fill colours to be edited Toggle strata on off switches strata fill colour on or off for example if printing to a monochrome printer you may prefer to switch the fill off Axes scaling individual x axis scales can be set for each plotted parameter The same option is available via the View menu Change axis scale s command Deflection down wall Active and passive total and effective stress profiles on either side of wall The default is to show total stress If effective stress is plotted water pressure will also be shown Bending Moment profile down wall Shear Force profile down wall Envelope Whereas other graphical results are for single stages envelope 5 the envelope of results for all stages in the calculation When the graphical output view is open the Graphics menu shows the following options File Edit View Globaldata Stage data Analysis window Help Scaling Font Save image Input Results F F w Toggle Strata Plot external x Y data Templates k Oasys Ltd 2014 Output 2 7 4 Batch Plotting Tabular results or graphical plots for several stages at once can be batch printed using the filter button Y on the main toolbar This will show the Prin
62. Value at Global Poisson s ratio battom node Wall plan length m Gradient Passive Softening LEFT RIGHT Excavation level J6 80 m 35 40 m Depth below excavation level 0 to softening surface m Haedistribute pressures Perform integral bridge calculations St th retention 5 100 hinimum equivalent fluid pressure rength retention 2 Nodes in Softening zone gt Mate 100 strength retention implies no global softening Seismic Analysis ta Eurocode 8 Perform seismic analysis Design ground acceleration 2 0 09 Analysis methad Gravity acceleration m s 3 8 Mononobe Okabe Kv ratio 0 Woods Seismic load application method Sail 5 Value for calculated Kh 1 5 nil Distributed load al base to 150 00 at top Point load at height from base f 0 5 Groundwater 9 Distributed load Point load at height f H from base f 0 333333 3 5 12 1 Model Type The type of soil model to be used must be selected here Further data is then requested depending which model is selected Safe method Wall Soil interface must be selected as or free Oasys Lid 2014 Frew Oasys GEO Suite for Windows 3 5 12 2 Mindlin method The Global Poisson s ratio and wall plan length must be specified Method of Sub grade Reaction Not available yet in windows version Boundary Distances When soil stiffness is represented using the Safe or Mindlin m
63. Wizard Stage Defaults The final wizard page reproduces most of the Analysis Data dialog and the values entered for analysis method wall soil interface lateral boundary distances and Young s modulus specification will be used in generation of all new stages Clicking Finish completes the wizard and creates Stage 0 with the input data The graphical input view will open to allow entry of node levels if these are being created manually If automatic node generation was selected the graphical input view will show a single soil zone extending the full depth of the problem More soil zones can be added as required to set up the initial ground profile Oasys Ltd 2014 Input Data 32 for Stage O otrut and surcharge data is added separately and additional stages created with the required stage changes before proceeding to run a stability check and full analysis 3 4 Global Data Global data can be accessed from the Global data menu or the Gateway The global data describes the problem as a whole All the material properties struts and surcharges which will be required for all subsequent stages must be defined here If using the Automatic Node Generation feature node levels are not required If using manual node entry the nodes must be placed in the correct locations to allow all subsequent construction stages to take place Note The location of the nodes can not be changed in a later stage It is useful to sketch out the prob
64. a Additional passive pressure due to load 2 ps 0 lt 2 2 lt Z lt pp 9 1 y p p 2B A 2B Wall and Strut Stiffness Matrices Wall Stiffness Matrices The wall is modelled as a series of elastic beam elements the stiffness matrix being derived using conventional methods from slope deflection equations Considering a single beam element of length L and flexural rigidity El soanning between nodes A and B the moments M and forces P at nodes A and B can be expressed as functions of the deflections and rotation at the nodes i e Oasys Ltd 2014 Detailed Processes in Frew On Mg 4 be 2 4 6E e ti e Where 0A and represent the deflections and rotations at nodes A and B respectively referred to the neutral axis of the beam The above equations can be re written in matrix form as M 115 1 B 8 G1 and P C 5 1 G2 E 2 where A B and C are functions of the element lengths and flexural rigidity El and and 0 are the nodal horizontal displacements and rotations If there no moments applied to the wall 0 can be eliminated to give S G3 in which S is the wall stiffness matrix given by 5 C AT 81 64 Oasys Ltd 2014 Frew Oasys GEO Suite for Windows 8 6 2 Strut or Anchor Matrices Struts or a
65. a plane of symmetry such as the centre line of the excavation The flexibility coefficients in the Safe model were derived for one specific geometric case which represented a ratio of L D of 10 where L is the distance to the remote boundary and D the depth of soil in front of the wall Oasys Ltd 2014 Frew Oasys GEO Suite for Windows 8 2 4 1 right Note Clearly as L D changes the flexibility coefficients will change and hence the stiffness matrix The greatest difference will occur at small ratios of L D i e large depth of soil in comparison to a close boundary In this case it may be more reasonable to use a sub grade reaction type of analysis where the spring length is well defined To allow for varying ratios of L D the Safe method has been modified by adding a single spring at each node point For high ratios of L D the spring stiffness is small due to the large spring length The results are then vrtually identical to those of the elasticity method alone For small L D ratios the single spring stiffness becomes dominant and controls and calculated wall movements Accuracy of Modelling Boundaries in Frew 5 test comparisons were carried out between Frew and Safe These were to determine the error in Frew due to the simplified assumption of an elastic soil which has 1 aconstant or 2 linearly increasing stiffness with depth These comparisons are described below Changes in wall pressure computed
66. ading stage 9 Wall and strut relaxation Oasys Ltd 2014 Input Data 28 The program recalculates the displacements and forces within the system at each stage Several activities can be included within a single stage provided their effects are cumulative For example it is appropriate to insert a strut and then excavate below the level of the strut in one stage but it is not correct to excavate and then insert a strut at the base of the excavation in one stage in doubt the user should incorporate extra stages The computer model of the program geometry should be drawn with the wall node locations carefully selected in accordance with the guidance given in inserting Nodes The nature of each problem will vary considerably and thereby the amount of data changes required for each construction stage Some information is compulsory for the initial stages Thereafter full flexibility is allowed in order to build up the correct progression of construction stages and long term effects Stage 0 amp Global Stage 1 Construction Long term data stages Compulsory Material properties Wall properties All materials Node levels Soil zones drained materials Analysis Method Convergence control parameters Optional Surcharges Analysis Method Analysis Method Wall relaxation Struts Convergence control Wall properties Analysis Method parameters Water Convergence control Convergence control Soil zones parameters parameters undraine
67. al The Basic Mindlin Model The method uses the integrals of the Mindlin equations which were published by Vaziri et al 1982 The integrals calculate the displacement at any point due to loading on either a vertical or horizontal rectangular area within an elastic half space If there were no rigid base or vertical loading the equations could be used directly to determine the flexibility coefficients of the nodal points due to horizontal pressures applied to the nodes assuming that the wall is at a plane of symmetry The flexibility of the soil with each side of the wall taken separately is equal to twice that of a half space The effect of the width W or out of plane dimension of the retaining wall can also be taken into account to some extent as the equations model the length of the pressure loaded rectangular area in the out of plane direction Clearly if this dimension is large a plane strain condition is modelled Plane of retaining Dis soll right wall Y mn left Oasys Ltd 2014 Detailed Processes in Frew 8 3 2 8 3 2 1 Application of the Model in Frew The soil being modelled in Frew by the Mindlin method is not an elastic half space and the effects of the assumed rigid base and vertical boundary should ideally be incorporated To take these boundaries into account additional boundary nodes are included when formulating the flexibility matrix as below Line af symmetry d soll s
68. alculations The fields should therefore be used to provide as many details as possible to identify the individual calculation runs An additional field for notes has also been included to allow the entry of a detailed description of the calculation This can be reproduced at the start of the data output by selection of notes using File Print Selection 3 4 1 1 Titles window Bitmaps The box to the left of the Titles window can be used to display a picture beside the file titles To add a picture place an image on to the clipboard This must be in a RGB Red Green Blue Bitmap format Select the button to place the image in the box The image is purely for use as a prompt on the screen and can not be copied into the output data Care should be taken not to copy large bitmaps which can dramatically increase the size of the file Remove To remove a bitmap select the button 3 4 2 Units This option allows the user to specify the units for entering the data and reporting the results of the calculations Oasys Ltd 2014 Units Quantity Conversion factor Displacement 1000 per m Force 0 001 per M Length level 1 per m Mass 0 001 per kg Stress 0 001 per Fa Reset Units Cm Ce Default options are the Systeme Internationale SI units and m The drop down menus provide alternative units with their respective conversion factors to metric Standard sets
69. anual override Ratio of maximum element length to minimum element length Maximum number of nodes that can be generated Toe level level From stability check m Mat calculate Override calculated toe level User specified toe level m Rigid boundary level m It allows setting of the node generation method automatic or manual some settings for automatic node generation and whether to calculate the wall toe level from a stability check lf a stability check has already been carried out this dialog will show the calculated toe level This can be overriden by the user Oasys Ltd 2014 51 Frew Oasys GEO Suite for Windows 3 5 Stage Data The Stage Data menu allows the data to be modified for individual stages using the Stage Operations window This opens a tree diagram as shown which then allows access to all available options for each stage Ticks are placed against those options which have been changed This window also allows the creation of new stages and the deletion of those no longer required When Add stage is selected the new stage can be inserted after any existing stage Parameters can also be set to change in a particular stage or not to change Sie Analysis 2 FREWman fwd Stage Operations Edit stage operations Define stage plot list Stage 0 Initial condition Stage 1 Insert Wallin Undrained Conditio Stage 2 Apply Plant Loading on Active 51 Stage 3
70. arly with depth e Inthe upper bound method a failure mechanism is considered The limits obtained necessary for stability but may not be sufficient Coulomb used an upper bound method to study the simplest failure mechanism a plane slip surface to derive the forces on a wall Horizontal Translation It is found that for the simplest case of all a frictionless wall translated horizontally without rotation their analyses give compatible results This result is therefore accurate both necessary and sufficient Note For one slip surface Coulomb s method only yields the total force on the wall In order to find the redistribution of that force i e the pressures on the wall further assumptions related to the mode of deformation are required For more complex problems involung wall friction and complicated patterns of deformation Rankine s simple assumptions about the pressure distributions are obviously wrong and Coulomb s planar slip surface is not the most critical Many other researchers have therefore derived information about active passive forces by studying other failure mechanisms In the absence of additional assumptions these methods yield the limiting force on the wall between the ground surface and any given point on the wall but they do not dictate the distribution of that force i e the pressures on the wall They produce limits which are necessary but not exactly sufficient However by seeking the most c
71. artial Factors that can be named and set to any value by the user Oasys Ltd 2014 9 Frew Oasys GEO Suite for Windows Code compliance User defined values Name of Partial Factors User defined values Factors Far material properties Fan 1 0 1 0 1 0 ri E 1 0 Factors Far Effects of Actions Applv partial Factor on effects of actions Partial Factor value 1 35 Document and cases is a pre defined list of code compliance Partial Factors Code campliance Code compliance User defined values User defined values Documents and cases Documents and cases EC Combination 2 2011 i CIRIA C580 Approach 12003 Cu o D Factors Far EFFecks of Actions Apply partial Factor on effects of actions Partial Factor value 1 35 Direct Kp Partial Factors can be applied even if earth pressure coefficients are User Specified Note When this set of Partial Factors is selected the Soil strength factors can not be selected and are set to Unfactored and to 1 0 Oasys Ltd 2014 input so Kp Partial Fackars Left Factor Right Factor Surcharges Partial Factors are applied to each type of load UDL or Strip and directly in the Surcharges table 3 4 8 Node generation data This dialog is available from the Global data menu or the Gateway H Frew1 Node generation data Node generation Type Automatic C3 M
72. artially submerged the g parameter differs for the wet and dry part of the stratum even though all other parameters are identical Hence two materials are needed to model the partially submerged material in the first stage These extra materials are generated and the appropriate 9 values for all the strata are calculated during the export process The following figures illustrate this situation Frew first stage material data Oasys Ltd 2014 Frew Safe Link L Frew Manual fwd Data Entry View BEA 25 kNim L n E 1 1 3 I hm m m m m om m m m om m o um um 5 30000 10 3500 4 000 Scale x 1 160 y 1 275 STAGE 0 Initial condition Frew Manual fwd Materials __ a JL E LE Jp pressure hi 20 0 0 60 User Specified 190 0 80 User Specified a Equivalent Safe first stage material data Safe1 General material properties ene uw etg Total weight cate Deform Drain amp KN Am L FL STRN 1 Fist Stage Material 1 Elastic Mohr Coulomb FL STRNH Draned 20 06 2 First Stage Material Elastic Mahr Caulomb PL STRN 20 086 Stage Material 3 Elas
73. assive limit This is an absolute value and the default value is 0 1 kPa Damping Coefficient The damping coefficient used in the analysis convergence is slow this can be increased If instability is apparent it may possibly be solved by reducing this The default value is 1 0 Oasys Ltd 2014 input Data 3 5 13 5 Maximum Incremental Displacement 4 1 Maximum deflection in one stage The default value is 1 0m Frew Safe Link Frew analyses the soil structure interaction of the retaining wall Frew calculates the pressures displacements etc at the wall However if one is interested in the movements of soil beneath the wall Frew will not be adequate However the same problem can be modeled in Safe The Frew Safe link feature enables the user to create a Safe model which is nearly equivalent to the Frew model This feature involves creation of a Gwa file The Gwa file format is a text format used by Oasys Gsa to transfer data across different programs The following steps are involved in the process 1 Validation of Frew data 2 Entry of wall data 3 Export of data from Frew file to Gwa file 4 Import of data from Gwa file to Safe file Data Entry The Frew Safe Link wizard is invoked by clicking on the Export To Safe button in the file menu On clicking the above mentioned button a file save dialog opens up and prompts for the name of a Gwa file to save the data After the user specifies the file name the ex
74. asys GEO Suite for Windows Pressure Depth Referring to the figure the criterion of p 2p means that the pressure p cannot drop below the limit of P This is the limiting condition used Frew when no redistribution of the wall pressures is specified It is sufficient to provide a conservative solution but may be unnecessarily severe If P is the force on the wall between depth z and the ground surface an alternative condition would be P gt P 0 5 in a uniform soil E2 0 2 gt dz Aree in a non uniform 501 0 2 0 These equations would allow the type of stress distribution indicated in the above figure which would occur for example at a propped flexible wall The equation E1 for a uniform soil is necessary but the following example shows that it is not sufficient Pressure Depth Consider the section of wall 2 Z in the above figure Above 2 the wall pressure p is in excess of Pa Equation E2 would therefore allow the pressure between Z and Z to fall to zero or even to have Oasys Ltd 2014 Detailed Processes in Frew 130 negative values provided that the area indicated as 2 does not exceed area 1 This is clearly wrong it is not admissible to have zero pressure on a finite length of wall supporting a cohesionless soil If it were the element of wall between 2 2 could be removed and no sand would flow out It would be
75. ate backfill stages of construction Insert Remove struts Insert Remove surcharges Long term Return to drained parameters effects Change groundwater conditions Use the relaxation option to model the long term stiffness of the wall To illustrate these operations a manual example is given below General layout of manual example Oasys Ltd 2014 Strip Load B strut 1 amp 2 anchors strut 4 Floor slab udl Excavation Stage 5 SUm boundary 0m boundary 21 Bp4 Modes 21 22 Rigid Boundary Combined stages shown here to aid placement of the nodes see Nodes The following shows the construction sequence separated into stages ready for modelling Note Soils 1 and 3 are Clay and have been used to represent the modelling of undrained material and the change to drained for long term conditions Soil 2 is a sand and thereby fully drained throughout the construction sequence Oasys Lid 2014 Frew Oasys GEO Suite for Windows stage 0 Initial condition drained stage 1 Insert wall in undrained conditions Pag stage 2 Apply plant loading an active stage 3 Apply anchor prestress side and excavate to 4 5m OD stage 4 Apply anchor stiffness stage 5 Excavate to final level of AL 5m OD and dewater stage Apply roof and basement stage 7 Undrained ta drained slab struts and remove ground anchor T T Stage 8 Remove plant lo
76. aterial 2 Convergence control 20 00 Material 2 Output 19 00 Maternal 2 Tabular oulput 18 00 Material 2 Graphca M o ee pg 9r pg 2 FrewSample fwd Output INITIAL DATA Tabular Output Notes Conversion of FREU DOS file to FREW Windows file Soll properties Mo Unit Wt Ka Xp Kac Xpc Kr Earth pressure kW m coefficients 1 20 00 0 600 0 200 6 000 0 894 4 899 0 200 User Specified 4 19 00 0 900 0 350 3 500 1 193 3 742 0 300 User Specified No y0 Gradient Gradient Drained of c xN n m kN n kN un u 1 00 02 20 50000 0 00 Draine 2 10 00 00 25000 0 00 Draine gt 4 Sui properties Vete Preobure No Stage Side Level Pressure Offset Width Ks en T es In XX n Uni pasive 1 0 30 00 25 00 1 000 2 000 1 000 Active Limit Strut properties 2000 200 00 No Stage Node Prestress Stiffness Angle a Scale x 1208 y 1 223 In Out xkN n m 1 n For Help press F1 1 3 1 Working with the Gateway The Gateway gives access to all the data that is available for setting up a Frew model Top level categories be expanded by clicking on the symbol beside the name or by double clicking on the name Clicking on the symbol or double clicking on the name when expanded Oasys Ltd 2014 About Frew 4 2 1 close up the item A branch in the is fully expand
77. axation to model long term behaviour of the wall For further information see Creep and Relaxation The wall relaxation is set to zero in following stages unless changed by the user 3 5 12 4 Fixed or Free Solution Free and fixed refer to restriction of the vertical displacements of the vertical faces of the left and right soil blocks where they interface with the wall and below the wall with each other This is relevant only to the elastic behaviour of the system not to the limiting stresses determined by specified values of When Free is used vertical displacement is permitted and soil blocks and wall behave as though the interface between them is lubricated transmitting no shear When Fixed is used the soil blocks are constrained at the interfaces with no vertical displacement Neither the vertical displacements in the Free case nor the shear stresses implied in the Fixed case are explicitly calculated by Frew However the stiffness matrices originally set up by Safe are different for the two cases Simpson 1994 has shown that allowance for vertical shear stresses reduces computed horizontal elastic displacements and this is significant in some cases Therefore the Fixed case will generally lead to smaller displacements and users may consider that it is closer to reality since there is generally little vertical displacement on the plane of the wall Neither case accurately represents the developmen
78. behaviour For drained behaviour the typical range of Kr would be 0 1 to 0 5 For undrained behaviour the same approach is applied to total stress In this case the undrained Poisson s ratio would normally be taken to be 0 5 where Kr 1 0 When filling the horizontal effective stresses in the fill material are initially set to times the vertical effective stress 2 4 2 Calculation of Earth Pressure Coefficients The equations presented below are taken from 1995 Annex They have been simplified to account only for vertical walls with a vertical surcharge on the retained side The following symbols are used in the equations angle of shearing resistance of soil degrees wall soil friction angle degrees f angle of ground surface to horizontal degrees The coefficient of horizontal earth pressure is given by Oasys Ltd 2014 Frew Oasys GEO Suite for Windows where 2 11 sing sin cos es expl2v tang cos SIE sing M ees cet 2 0 sin tn 2 p m and v have units of degrees However v must converted into radians before substitution into the above equation for evaluating K For calculation of active earth pressure coefficients the angle of shearing resistance of the soil and the wall soil friction angle must be entered as negative values For calculation of passive earth pressure coeff
79. by Frew and Safe were compared for the same wall movements for varying ratios of L D The comparisons were achieved by calculating the wall movements due to an excavation using Frew and then using the calculated movements as input data for a finite element analysis using Safe The behaviour was fully elastic in both cases With the same specified horizontal wall movements the changes in stress calculated by Safe are saf comparison between AP safe gives an indication of the agreement between the two methods of analysis The Model In the Frew analysis the wall was taken as extending to a depth of 25m below ground level and the rigid boundary was at a depth of 28m The dig depth was 5m giving 20m of soil in front of the wall The distance to the remote boundary on the left side of the wall was taken as 1000m and on the right side the distance was varied to give L D ratios of 0 25 0 5 1 0 2 0 4 0 and 50 0 Oasys Ltd 2014 Detailed Processes in Frew 120 L leff 1000 m T I Liright m 5 75 11 5 23 0 4 0 92 0 1150 0 23m UR ROM CO D c SUD OKNMAma E1 ADD M m FSUDUEMA mz Comparisons were made for soil which has a constant Young s modulus E1 throughout its depth equal to 40 000kN m and also for a soil in which Young s modulus E2 increased linearly from 5 000kN me at ground level to 75 000kN me at a depth of 28m The soil is assumed t
80. c to base of problem Oasys Ltd 2014 Detailed Processes in Frew Berm strip load surcharge and calculation of passive pressure beneath berm The above procedures may get the active pressures slightly wrong but that is of little consequence generally for berms The procedures may cause the program to fail however with a message saying the active pressure is greater than the passive pressure at a node under the berm If this occurs the active coefficient in the material under the berm should be reduced 88 2 Simplified Procedure This method is considered to be conservative but simpler to use than that presented above It relies on the fact that in calculating passive limiting pressures Frew only considers uniformly distributed surcharges UDLs and ignores the beneficial effects of strip surcharges 1 For contact stresses between the berm and the wall proceed as for the Rigorous Method above with Steps 1 and 2 2 At the level of the base of the berm the level of node b the figure above apply a negative UDL surcharge q yh Atthe same level apply a positive strip surcharge representing the berm itself This will have a pressure equal to and width A as defined in the figure in Rigorous Method Below the berm normal values of coefficients of active and passive pressure may now be used Possible slips of Type C and D should be briefly reviewed though it is unlikely that these will ever give a problem
81. ces The user is deemed to be conversant with standard engineering terms and codes of practice Itis the users responsibility to validate the program for the proposed design use and to select suitable input data Printed May 2014 Frew Oasys GEO Suite for Windows Table of Contents 1 About Frew 1 1 1 General Program X SS DAP 1 p Program 5 t 1 1 3 Components of the User Interface 0 nenne nenne nnne nennen nnn 3 1 31 Working WITH the Gate WAY eh uoce ae eurer 3 2 Methods of Analysis 4 NM Stability CHECK ng 4 2 1 1 Fixed Earth Mechanisms e eorr erre nnne 4 2 1 2 Free Earth MechaniSm S 5 2 1 2 1 propped W cT RR 5 2 1 3 Active and Passive Lim its
82. chanism would not occur Oasys Ltd 2014 Detailed Processes in Frew 132 8 4 3 Iterative Technique Adopted Frew In order to ensure that active and passive limits are not violated displacement corrections are computed for each node and added to the displacements derived from elastic analysis They are displacements associated with plastic strain in the body of soil When displacement corrections are used the wall pressure at any node is still influenced through the elasticity equations by the movement of nodes below it but may be independent of its own movement and of the movement of nodes above it Line af cai H Failure 7 1 Surface t Modes Suppose an active passive failure occurs as shown above The displacement corrections applied to ensure that the limits are not violated at node q will cause a change of stress but no displacement at node r whilst at node p there will be a change of displacement but no change of stress Effectively this means that movement is taking place at constant stress on the failure surface whilst elastic conditions are still maintained separately in the blocks of material on either side of the failure surface The following procedure is used to achieve an iterative correction for wall pressures in the program The procedure starts at the top of the wall and works downwards 1 For node i calculate the correction FORCOR to the force between soil and wall required to return to
83. contains the following options Problem geometry Enter the levels of the top node and the lower rigid boundary This will set the correct range in subsequent graphical display Materials Add or delete materials Clicking Add material opens a further dialog allowing input of basic material data Oasys Ltd 2014 1 Frew Oasys GEO Suite for Windows 3 3 3 Node generation Wall toe level Material Data Description Sandy clay Unik weight kM Irn 18 Stiffness strength parameters Constant Varying with depth Reference level y0 EO kM rn 20000 kA Gradient af E Gradient of c Earth pressure coefficients Calculated O Specified Fhi Delkafphi Beta Clic ratio ey 0 5 This data entry method will be sufficient in many cases but some other settings for example undrained pore pressure calculation parameters need to be set later in the normal Materials table Automatic will allow all data input to be specified by level and node positions are generated by Frew Manual means that node positions must be entered by the user and most other data must be specified by node number rather than level Selecting Obtain from stability check will enable the user to run a stability check before full analysis to estimate the required toe level This can be manually overridden if required To enter a known required toe level select Enter manually and enter the level New Model
84. d assuming movement of the nodes b The stiffness matrices representing the soil on either side of the wall and the wall itself are assembled c These matrices are combined together with any stiffness representing the actions of struts or anchors to form an overall stiffness matrix The incremental nodal displacements are calculated from the nodal forces acting the overall stiffness matrix assuming linear elastic behaviour e The earth pressures at each node are calculated by adding the changes in earth pressure due to the current stage to the initial earth pressures The derivation of the changes in earth pressure involves multiplying the incremental nodal displacements by the soil Stiffness matrices f The earth pressures are compared with soil strength limitation criteria conventionally taken as either the active or passive limits If any strength criterion is infringed a set of nodal correction forces is calculated These forces are used to restore earth pressures which are consistent with the strength criteria and also model the consequent plastic deformation within the soil g A new set of nodal forces is calculated by adding the nodal correction forces to those calculated in step a h Steps d to g are repeated until convergence is achieved i Total nodal displacements earth pressures strut forces and wall shear stresses and bending moments are calculated 2 3 Soil Models The soil on both sid
85. d failure surfaces and finite element work for soil that has constant properties with depth The ranges of variables considered were as follows a 15 to 60 b q B from 0 33 to 5 and C A B from 0 to 2 he Application in Frew It is important that any approximation that is chosen should be generally conservative In the case of active pressure this can generally be achieved by over estimating the pressure near the top of the wall Oasys Ltd 2014 Detailed Processes in Frew 134 CHANGE INACTIVE PRESSURE A CM LIMIT DUE 5 SURCHARGE Wall 04 03 02 01 o v B T Total area to m equal ilg KEY Model Experimental curves 5 a Line B Approximation to represent the change in b Distribution af change Comparison of approximation active pressure limitation due to surcharge in active farce with results of parametric study The results showed that the log spiral method which is considered to be the best available approximation usually gave very similar results to the straight line method From theoretical considerations the approximation illustrated above was developed to represent the increase in the active pressure limit thus transferring the vertical pressure to a horizontal pressure on the wall This shows the shape of the pressure limit diagram and the criteria for calculation It should be noted that if the width of the load B is s
86. d or drained materials Soil zones Soil zones drained undrained or drainedmaterials Excavation or filling materials Surcharges Surcharges Excavation or filling Struts Struts Surcharges Water Water Struts Water Oasys Lid 2014 E Frew Oasys GEO Suite for Windows 3 2 Preferences The Preferences dialog is accessible by choosing Tools Preferences from the program s menu It allows the user to specify the units for entering the data and reporting the results of the calculations These choices are stored in the computer s registry and are therefore associated with the program rather than the data file All data files will adopt the same choices Preferences Numeric Format Company Info Engineering significant Figures Decimal decimal places Page Setup Scientific significant Figures Smallest value distinguished From zero 006 Restore Defaults t Save File every 10 minutes Show welcome screen Begin new Files using the Mew Model Wizard Numeric Format controls the output of numerical data in the Tabular Output The Tabular Output presents input data and results in a variety of numeric formats the format being selected to suit the data Engineering Decimal and Scientific formats are supported The numbers of significant figures or decimal places and the smallest value distinguished from zero may be set here by the user Restore Defaults resets the Numeric Format specifications to prog
87. depth APFREwW APSAaFE 1 0 21 3 0 40 L D Ratio 8 2 5 Friction at the Soil Wall Interface Frew offers two options for representing the soil wall interface friction 1 Free represents a frictionless interface 2 Fixed full friction Free Surface anil v 0 3 Loaded Height 101 elements Boundary Length L 10 H unequal elements Rough Rigid Boundaries Safe model These options select from the two sets of pre stored flexibility matrices computed by Safe for the nodes on boundary AB The two sets represent nodes free to move vertically or fixed vertically respectively Oasys Ltd 2014 123 Frew Oasys GEO Suite for Windows 8 2 5 1 8 3 1 Accuracy of the Fixed Solution In many situations when props or struts are being used fixed and free give similar results An exception is a cantilever situation where the fixed method will give less displacements because it models greater fixity between the soil and wall It must be noted that the case with interface friction fixed is somewhat approximate because Poisson s ratio effects are not well modelled For example these effects in a complete elastic solution can cause outward movement of the wall when there is a shallow soil excavation Approximations Used in the Mindlin Method This method is similar to the Safe flexibility method in that the soil on each side of the wall is modelled as blocks of elastic materi
88. der to generate a roughly equivalent pore pressure distribution in Safe the pore pressures are calculated at locations midway between the Frew pore pressure data points Oasys Ltd 2014 Frew Safe Link Frew piezometric data Safe piezometric data points points Pore pressure profile oafe plezometric points midway between Frew piezometric points 4 2 8 Unsupported Features The following features are currently not supported by the Frew Safe Link feature Free soil wall interaction Passive softening Generated Young s modulus profiles e Minimum equivalent fluid pressure Wall relaxation Mindlin model e Sub grade reaction model e Seismic assessment 5 Integral Bridge Analysis Frew can be used to perform integral bridge analysis This analysis is based on PD 6694 1 In this analysis strut loads representing the expansion and contraction of the bridge are applied in consecutive stages New stages corresponding to deck contraction in winter and deck expansion in summer are added as the analysis proceeds The analysis continues until the convergence in the d H values at the front and back of the wall are achieved Oasys Ltd 2014 Frew Oasys GEO Suite for Windows 5 1 Data Entry To use the integral bridges analysis feature the following steps are required 1 All the stages up to integral bridge analysis should be defined as before i e if there are 3 stages before initial winter contraction these
89. e British Library excavation indicated that the formulae were reasonable approximations giving displacements roughly 20 too large However this may be very dependent on the geometry of a particular problem it is also dependent on the approximations used in Frew to represent elastic blocks of soil of finite length see Approximations used in the Safe Method Modelling Berms Consider a berm of depth d effective unit weight y and effective weight W The behavour within the berm will be quasi elastic until a failure plane develops It will also be elastically connected to the ground beneath until a failure develops In the elastic phase there will not be much difference in stress distributions between a berm and a uniform layer of the same height In both cases horizontal forces at the wall are transferred downwards by shear The elastic behaviour therefore can be modelled as if the berm were a complete layer of soil Berm Geometry The figure shows three possible types of failure surface These will develop at different stages depending on the types of soil in the berm and in the ground beneath A particularly critical case occurs when a berm of frictional soil overlies frictionless ground It is possible for example that wall pressure above failure surface A will cause failure on surface B whilst surface A is still intact The user should propose equivalent values of K and c call them K Koc and c from which Oasys
90. e analysis data Kp curves A B E F Stiffness curves E EIN Material 7120 Keve du Brg ve Tabular output 7 Graphical output Standard 6N 6P BN 6P 30 Standard 30 Standard 6N 6P Lse Gran 90 Coh Gran 70 Standard 6N 6P 22 Winter2_ AA 2 ter_D1p5_H10 fwd Struts i Node Prestress Stiffness Lever arm number kN 7m kN m m m 2 0 00 3913043 00 0 00 130434800 3564 00 0 00 5 Once the data has been entered the user can go for the analysis in the regular way When the user clicks the Analyse button the program performs normal analysis for all the non integral bridge stages If these previous stages are analysed successfully it will first apply initial winter contraction about half the prestress specified for the deck strut followed by cycles of full winter contraction and full summer expansion until convergence in d h values is achieved First d h value is found for the left side Subsequently the above procedure is repeated on the right side During the analysis the program automatically adds the necessary stages 6 After analysis the user can view the actual material properties used in integral bridge stages in the results output as shown below Oasys Ltd 2014 Integral Bridge Analysis 2 ES Winter2 2 D1p5 HT10 fwd Output
91. e derived for elastic soil the calculated Frew coefficients can be scaled by the ratio of the Safe element length to the Frew element length This gives an equivalent total load at the Frew node of unity In general the Frew node will not correspond directly with a Safe node and in such circumstances a second level of interpolation is implemented Two sets of Frew flexibility coefficients are calculated which correspond to the Frew element centred on the Safe nodes immediately above and below the Frew node The actual Frew flexibility coefficients used in the calculations is then taken to be a weighted average of these two sets of coefficients Oasys Ltd 2014 Detailed Processes in Frew 8 2 3 Accuracy with Respect to Young s Modulus E The flexibility matrices that have been computed using finite elements are effectively accurate for two situations 1 Young s modulus constant with depth 2 Young s modulus increasing linearly from zero at the free surface No precise theory is available to enable accurate matrices to be derived for other cases and various intuitive methods have therefore been adopted These have been tested by comparing flexibility matrices computed by Frew with the results of additional finite element computations using Safe 8 2 3 1 Linear Profile of E With Non Zero Value at the Surface A case of particular importance is that of a linear profile of Young s modulus with a significant non zero
92. e modelled Use two struts at the required level which give the correct short term stiffness when combined Then remove one of them to obtain the long term effect Note In Frew when a strut is removed the force associated with it is also removed Oasys Ltd 2014 15 Frew Oasys GEO Suite for Windows 8 10 Undrained to drained behaviour Manual Process To effect a switch from undrained to drained behaviour without using Frew to calculate the undrained pore pressures the following procedure should be carried out The user must first calculate and specify the profile of undrained pore pressures then change them to the drained values Note lt is not sufficient merely to change to effective stress parameters and impose the final drained distribution of pore pressure The following procedure has been found to be satisfactory Note In the Frew tabular output data apparent horizontal effective stress Vo apparent vertical effective stress u 1 pore water pressure specified by the user Tabulate the values of vertical and horizontal effective stresses given by Frew for Stage 0 or the previous drained stage for both the left and right sides of the wall Add the user input values of pore pressure u to obtain the total stresses Tabulate the corresponding values for the final undrained stage in the analysis Calculate the change in total horizontal Ao and vertical Aoc stresses between the two stage
93. e retained side is assumed to be 1 cm above the rotation strut e Any soil layers above this assumed ground level are treated as equivalent surcharges e The ground water distribution is also applied starting from the assumed ground level However the pore pressure from the level of rotation strut downwards are same as the original pore pressure distribution The pore pressure from the level of assumed ground level to the level of rotation strut is assumed to vary linearly Oasys Ltd 2014 Methods of Analysis Tolerance Strut 3 1 Equivalent surcharge from soil above the rotation strut Pore pressure distribution Tolerance is related to the assumed location of ground level above the location of lowest strut This Is currently taken as 1 cm e Any strip surcharges that are present above the location of rotation strut are modelled as equivalent strip surcharges at the level of the lowest strut The load intensity and width of this equivalent surcharge are calculated using 2 1 rule for diffusion of vertical stress in soil Oasys Ltd 2014 Frew Oasys GEO Suite for Windows Strut 2 H Strut 3 In the example above Q 2 W Q W W W 1 2 H 1 2 W H where W width of the strip surcharge Q load intensity of the strip surcharge in kN m W width of equivalent surcharge Q load intensity of equivalent surcharge in height of the strip surcharge above the leve
94. e seismic analysis feature the following steps must be followed 1 First set up a Frew analysis as normal 2 Via the stage tree dialog add a further stage for the seismic analysis this must be the final stage of the analysis 3 Go to the Analysis method dialog for the seismic analysis stage and click on the Perform seismic analysis check box Ch208LS Seismic fwd Analysis data Analysis method SAFE Mindlin interface Free Fixed Wall relaxation global Poisson s ratio Wall plan length m Haedistribute pressures Perform integral bridge calculations Minimum equivalent fluid pressure Seismic Analysis to Eurocode 8 Perform seismic analysis Analysis method Mononobe Ok abe Woods Seismic load application method Soil Distributed load Boundary distances m LEFT 50 Young s modulus Specified Youngs modulus data LEFT Value at bottom node 0 Gradient Passive Softening Excavation level Depth below excavation level to softening surface m Strength retention Nodes in Softening zone gt RIGHT 50 Generated LEFT RIGHT ge Sn m 35 40 rn Note 1004 strength retention implies na global softening Design ground acceleration m z 0 09 Gravity acceleration m z 3 81 Kv ratio vl Eh 5 Value for calculated Kh 1 Hn at base ta 150 00 at top Point load at height F H from base t
95. ecome triangular The additional active pressure due to the surcharge is replaced by a series of equivalent forces These act at the same spacing of the output increment down the wall Thus a smaller output increment will increase the accuracy of the calculation Varying values of k If the active pressure coefficient k varies with depth the program chooses a mean value of k between any depth z and the level of the surcharge Stawal then imposes the criterion that the active force due to the surcharge down to depth z be equal to the force derived from the diagram in above This is then subjected to the further limitation that the pressure does not exceed qk where q surcharge pressure active pressure coefficient to depth z Groundwater Flow Water flow beneath the base of the wall can be modelled by setting the Balance water pressures switch in the Stability Check dialog box The program uses the following iterative process Hydrostatic Profile uf uf 1 Carry out initial calculation using input water data to obtain the first estimate of embedment of the wall 2 Calculate U for embedment d Alter the ground water gradient either side of the wall by specifying a piezometric pressure equivalent to U at the base of the wall where 10 Oasys Ltd 2014 11 Frew Oasys GEO Suite for Windows 3 Re run the Stability analysis 4 Check calculated value of d 5 Repeat steps 2 to 4 unti
96. ects of excavation and backfill Cohesion referenced at yO and taken as either C for drained soil or Cu for an undrained soil Reference level for the gradient of cohesion c or Young s modulus E with depth Tab across the column if they are constant with depth Note This level does not have to correspond to the top of the material layer It is a reduced level and is not referenced from the bottom of the layer The rate of change of cohesion with depth A positive value means cohesion is increasing with depth The rate of change of Young s modulus with depth A positive value means stiffness is increasing with depth Indicates whether the material is Drained or Undrained Note This setting is only used by Partial factors and Passive softening to access drained undrained soil strength properties For undrained materials only factor to use in weighting the failure envelope on the dry side between Mohr Coulomb and Modified Cam Clay envelopes Default is 1 Used only in calculation of undrained pore pressures see Undrained Materials and Calculated Pore Pessures For undrained materials only the number of the material from which to use effective stress parameters in undrained pore pressure calculations Note the user should set the last column to zero if undrained pore pressure calculations are not required Frew Oasys GEO Suite for Windows y Sail Vo fone Gradient c 22 Gradient E 55 l
97. ed unit weight of the soil for calculation of lateral earth pressure Select either pervious or impervious Pervious indicates that the soil is highly pervious to water flow and the load from the soil structure and water are calculated separately Impervious indicates that water will move with the soil and that they will act together Pervious Impervious Derivation of Kh Either user specified or calculated r The r value for calculated Kh see Table 7 1 of EN 1998 5 2004 The lateral soil pressure coefficient If user specified this must be entered Kh pen manually otherwise the calculated value will be shown in this box value is dimensionless thrust factor used in Wood s method This is frequently assumed to be 1 Ess is the small strain stiffness of the soil Where only small displacements Ess of the retaining wall are anticipated an alternate small strain stiffness may be entered by the user The rate of change in small strain stiffness with depth A positive value Gradient Ess indicates stiffness increasing with depth Note that the reference level for each material is as set in the general material parameters table 6 Having set the seismic parameters next analyse the file During analysis strut forces will automatically be generated and applied to the final stage representing the seismic force due to the soil movement These strut forces can be in the Struts table following analysis but will
98. ed when the items have no symbol beside them Double clicking on an item will open the appropriate table view or dialog for data input The gateway displays data from the current stage under Data for Stage node The data items which have changed from the previous stage are indicated by bold font Methods of Analysis Frew is used to compute the behavour of a retaining wall through a series of construction sequences Displacement calculations are complex and involve considerable approximations It is essential therefore that the user understands these approximations and considers their limitations before deciding which type of analysis is appropriate to the problem The main features of the computations are summarised here Further details are presented in the section on Detailed Processes Frew A summary of the Frew analysis for inclusion with the program results and project reports is included in Brief technical description Stability Check The stability check calculations assume limit equilibrium i e limiting active and passive states either side of the wall These pressures are used to calculate the required penetration of the wall to achieve rotational stability Support for partial factor analysis is now available in the program The user may specify this in Partial Factors dialog Two statically determinate mechanisms in the form of Fixed earth cantilever and Free earth propped retaining walls can be
99. eg renen ast En hne CU S E mane CREE RO MR 137 emet pea dida ttn dc Vcn aa 137 09 24 JBISgUlF emerit A iene cierta oct ox teni o p D CERE CA ela PURSE v enc anv Due EE D 138 8 6 Wall and Strut Stiffness 139 8 6 1 Wall Stiffness Matrice ars Sex ev ec ciae ed Ce Ey Cu e eee Seres poca eal usi Penes 139 8 6 2 Strut or Anchor Matrices s Dena Desa essa ag sag sag any ans ana annus nass 141 8 7 Modelling Axi symmetric Problems Using Frew 11111 142 8 7 1 Soil Inside the Excavation 5 143 Oasys Ltd 2014 Contents 8 7 2 Soil Outside the Excavation 144 8 7 3 Varying with Depth siiis cisci ses ci
100. ei 53 3 59 Editing Stage an EDS ND a bul FD 53 3 5 6 Editing Stage ripsari iino Drap ot Peine i 54 3 5 7 Apply Remove Surcharges 1 3 3 1 1 3 35 nnn nnn nans n nass SADA snas 55 3 9 9 INS OEE Remove xor or trux Fu Ee CE EE 55 3 99 G0I1LZOHBS dV cu M M E t M S 56 3 5 9 1 Digi Fill OPS alli reus buit ec Dri EE MER YER cal UEM 59 3 5 10Wall enses a also M IL 60 62 3 94 2AnalysIS Data eni E og M Ud cadat ian ten d s Ed dE 65 29121 cH MPH 66 39 122 Boundary Distances sedusir TIU I 67 91253 Nc eU a ar a 68 3 5 12 4 Fixed or bh limen 68 3 9 12 5 ourndgs Modulus E E a O 68 3 5 12 6 Pedistrib tion Of Pres res cur CV E EFC e DO va
101. ence limits a The effective earth pressure is less than the Coulomb limit but still greater than the redistributed active pressure limit p The effective earth pressure is greater than the Coulomb limit but still less than the redistributed passive pressure limit r The effective earth pressure is greater than the redistributed passive pressure but not sufficient to cause a failure to the surface see Calculation of Active and Passive Limits and Application of Redistribution on page 58 m The earth pressure reported is the Minimum Equivalent Fluid Pressure MEFP where this has been specified Note that a p and r are only used when redistribution is used to calculate active and passive pressure limits Warning or error messages will be shown in both the Solution Progress window and on the detailed results if any stage has failed to analyse or has high bending moments below the base of the wall Most are self explanatory but some additional detail is given below Analysis not converged within specified number of iterations Try increasing the number of iterations in the Convergence Control dialog for the relevant stage This error may occur in Stage 0 where a surcharge is applied at ground level before the wall has been installed This occurs where it creates a discontinuity in the lateral earth pressures at the top node Where this occurs this can usually be worked around by applying the surcharge at a level slightly below the ground sur
102. er e and r a factor representing the ratio between the acceleration value producing the maximum permanent displacement compatible with the existing constraints and the value corresponding to the state of limit equilibrium Vertical Seismic Coefficient Kv The vertical seismic coefficient is calculated using the ratio of Kv to Kh Rk and the horizontal seismic coefficient such that Kv Rk x Kh 6 2 2 Wood s Method Wood s method provides a simple calculation to determine the dynamic soil force on a retaining wall during a seismic event k yH For which k is the horizontal seismic coefficient the soil unit weight and H the retained height of the soil Wood s method is supported by the research detailed in Wood 1973 which presents the results from a range of simulations calculating the maximum dynamic pressure on the back of rigid retaining walls The method is then described in later works e g Wood amp Elms 1990 The simulations supporting this method assume a homogenous fully elastic retained soil and stiff Oasys Ltd 2014 Frew Oasys GEO Suite for Windows 6 2 3 underlying material As a result where multiple strata are present behind the retaining wall a weighted average is taken for the parameters k and such that _ d2nknn 2 ZnYn kn H and Where n represents the layer number and 2 the layer thickness as shown the following example figure Layer 1 71 Khi Layer 2
103. es of the wall is represented as a linear elastic material which is subject to active and passive limits Three linear elastic soil models are available in Frew 1 Safe Method 2 Mindlin Method 3 Sub grade Reaction Model Note The sub grade reaction model is not currently active it will be added to Frew in the near future All use different methods to represent the reaction of the soil in the elastic phase Oasys Lid 2014 E Frew Oasys GEO Suite for Windows 231 Safe Method This method uses a pre calculated soil stiffness matrix developed from the Oasys Safe program The soil is represented as an elastic continuum It can be fixed to the wall thereby representing full friction between the soil and wall Alternatively the soil can be free assuming no soil wall friction see Fixed or Free solution Accuracy of the Safe solution This method interpolates from previously calculated and saved results using finite element analysis from the Safe program The method gives good approximations for plane strain situations where Young s modulus is constant or increases linearly from zero at the free surface For a linear increase in Young s modulus from non zero at the free surface the results are also good but for more complicated variations in layered materials the approximations become less reliable In many situations when props or struts are being used fixed and free give similar results An exception is a
104. ethods it is assumed that the lowest node specified in the data defines a horizontal rough rigid boundary For details on inserting Nodes The rigid boundary should be set at a level where the soil strain due to excavation or loading is expected to have reduced to near zero Wall Sail to left of wall RE opil to right af wall soil type 4 nil type 5 Soil type 3 VERTICAL RIGID BOUND ARY Modes VERTICAL RIGID BOUNDARY RIGID BASE The distances from the wall to rigid vertical boundaries to the LEFT and RIGHT are also required For the Safe and Mindlin methods the vertical boundaries can be used to represent 1 aplane of reflection in a symmetric excavation 2 Orthe limit at some distance from the excavation beyond which soil strain is expected to have reduced to zero Note The specified distances can be different on either side of the wall By restricting the distance at which deformation can occur the effects of an excavation of limited length can be achieved For further information see Modelling Axi symmetric Problems Using Frew In the Sub grade reaction method the vertical boundary distances are used to represent the length of the soil spring at each node Spring lengths may be specified for each node and different values Oasys Ltd 2014 input Data 68 may be given on the left and right sides of the wall 3 5 12 3 Wall Relaxation From stage 2 onward it is possible to specify a rel
105. evel wy co Grad c yo y E Eo Grad E yo y 3 4 4 Nodes The Node level entry data is only available if automatic node generation is switched off in the New Model Wizard or the Node generation data dialog Nodes can then be entered by using the graphical or tabular display and are required at the following locations 1 Strut levels 2 and base of the wall and levels at which the wall stiffness El value changes 3 Levels either side of the ground surfaces during excavation back fill and the interfaces between soil zones Note 1 Ground surfaces and soil zone interfaces occur midway between nodes The exception is the highest ground surface which can coincide with the top node Note 2 Where seismic analysis is undertaken and the seismic force is applied as a point load struts will be generated at the location in which the forces are to be applied As a result nodes are also required at these levels Oasys Ltd 2014 Input Data rita S erac dedi dione ied 1 Cg c cce sd p Durs L Enos Y Lc c cru cr 1 Amos Current selection Nodes 28222 B H Lj m STAGE initial conditi
106. face Vertical effective stress lt 0 Oasys Ltd 2014 Frew Oasys GEO Suite for Windows This means the data is such that the pore pressure exceeds vertical total stress see Total and Effective Stress This is usually caused by a data input error Active gt passive at iteration on the L or R side at node n If the iteration number is 1 this is probably due to soil properties and surcharges of limited extent being prescribed such that the active pressure exceeds the passive pressure at the node indicated lf is equal to 2 or more this message usually implies the solution is becoming numerically unstable WARNING Residual moment 196 of peak moment in wall WARNING Wall base moment 2096 of average wall moment These warnings are output if the program obtains relatively high bending moments below the base of the wall This can happen if the displacement of the wall is large compared with the flexure so curvature cannot be computed with sufficient accuracy need to have several significant figures of difference of displacement and gradient of displacement between adjacent nodes The problem is generally caused by small stiff elements and can usually be overcome by increasing the distance between nodes If these warnings are given they indicate that the wall is not in equilibrium and the results are not reliable 7 3 Graphical Output Graphical output of the data and results is accessed via the View menu o
107. fect of the struts are incorporated into the analysis by matrix addition of the expressions given above to those given in equations G1 and G2 see General Elimination of 0 gives the following expression which is comparable to equation G3 P D 151151 G12 The new stiffness matrix for the wall S including the effect of the struts and the effect of the prestress D are given by S C S A S I S 15 G13 D 1 S 1 5 P L sina G14 Of particular interest is the special case of a strut inclined at 90Deg to the wall for which equation G6 reduces to 1 8S L G15 which allows moment restraint to be modelled at any node 8 7 Modelling Axi symmetric Problems Using Frew Frew provides facilities for analysis of a plane strain excavation i e an infinitely long trench L of excavation Axi symmetric problem Many excavations are roughly square and St John 1975 has shown that these can be modelled approximately as circular For an axi symmetric analysis the results apply to mid side of the square Oasys Ltd 2014 Frew Oasys GEO Suite for Windows Once props have been inserted into an excavation it makes little difference to the behaviour of the section being analysed whether the excavation is infinitely long or circular This is because most of the strains which cause displacements are concentrated close to the prop
108. g a strut with an inclination of 90 degrees and a non zero lever arm together with an applied pre stress force or a stiffness respectively Modelling of Anchors Stressing an anchor may be modelled by specifying a strut with a pre stress force equal to the stressing force and a zero stiffness The stiffness of zero would maintain a constant force at the point of application throughout the analysis In subsequent stages after the anchor is locked off it is usually convenient to remove this strut and insert a strut that models both the pre stress and stiffness of the anchor Inclined anchors are modelled by specifying an inclination to the horizontal and if they are not applied at the vertical axis of the wall a lever arm can be specified to allow for this see Strut Properties Oasys Ltd 2014 Input Data 3 4 6 Surcharges Surcharges be applied at or below the surface of the ground on either side of the wall These are always uniform pressures and may be in the form of 1 Strip loads of any width running parallel to the wall or 2 Uniformly distributed loads of infinite extent Width Offset gt strip Load Unitormally Distributed Load u dl LEFT The input data required for each surcharge is as follows FREWman_V19 1 fwd Surcharges m 3d me RE A Surcharge ag Side Mar E Type ET Partial Factor Ee is Defaults Left 1 00 1 _ 2
109. ges before bebe integral ummer exparnstiorn inter contraction analysis and delete all soil pressure history bridge analvsis and delete all New D H values are New D H values are data soil pressure calculated at back of wall calculated at front of wall history data Are new D H values Are new D H values behind wall significantly infront of wall significantly different from current D H different from current D H values values No No STOP STOP 6 Seismic Analysis Frew can be used to perform seismic analysis of a retaining wall This analysis is undertaken based on Wood s method and the Mononobe Okabe method These are pseudo static methods that estimate the additional lateral dynamic soil load on the wall In this analysis struts representing the dynamic soil and groundwater loads are applied to the wall There are a range of methods available to assess the impact of seismic events on retaining walls and the methods used by Frew will not be suitable in all cases As a result it is important to confirm with a seismic analysis expert that the methods used are suitable before analysis is undertaken Additionally loads other than the dynamic soil and groundwater may be applied if there are likely to be other loads applied to the wall e g due to adjacent structures consideration will need to be given as to how these are taken into account Oasys Ltd 2014 6 1 Data Entry Seismic Analysis use th
110. hnical Description 16 Safe finite element program This method is ideally limited to a soil with linearly increasing stiffness with depth but empirical modifications are used for other cases 2 Mindlin method the soil is represented as an elastic solid with the soil stiffness based on the integrated form of the Mindlin Equations This method can model a wall of limited length in plan but is ideally limited to a soil with constant stiffness with depth but again empirical modifications are used for other cases 3 Subgrade reaction method the soil is represented as a series of non interactive springs This method is considered to be unrealistic in most circumstances The program analyses the behaviour for each stage of the construction sequence At each stage it calculates the force imbalance at each node imposed by that stage and calculates displacement and soil stresses using the stiffness matrices If the soil stresses are outside the active or passive limiting pressures correction forces are applied and the problem solved iteratively until the stresses are acceptable Allowance can be made for arching within the soil body when calculating the active and passive limiting pressures The following input parameters are included in the analysis problem geometry including dig depths distances to remote boundaries wall profile bending stiffness and creep soil stratification strength density and stiffness struts or anchors including
111. icients positive angles should be used For both active and passive earth pressure coefficients the value of J is positive for a ground level which increases with distance from the wall Oasys Ltd 2014 Methods of Analysis te ACTIVE PASSIVE TUe n 2 5 Total and Effective Stress Frew recognises two components of pressure acting on each side of the wall 1 pressure This is prescribed by the user and is independent of movement 2 Effective stress Pe This has initial values determined by multiplying the vertical effective stress by the coefficient of earth pressure at rest Thereafter its values change in response to excavation filling and wall movement The vertical effective stress is calculated as 2 Quim HU t Oui 2 where Prescribed pore pressure g unit weight 2 _ level Zs surface level vertical stress due to all uniformly distributed surcharges above level z Oasys Ltd 2014 EM Frew Oasys GEO Suite for Windows 2 5 1 2 5 2 Drained Materials Effective stress and pore pressure are used directly to represent drained behavour Note The pore pressure profile is defined by the user and is independent of movement Undrained Materials and Calculated Pore Pressures Frew can be requested to calculate undrained pore pressures at each stage The feature is available in the Material Properties table and is activated by
112. if the soil is undrained take vc 0 5 Therefore for an undrained soil using the Safe model the distance to the internal rigid boundary 0 5 0 91 0 55 radius of the actual excavation 8 7 2 Soil Outside the Excavation The same simplifying assumptions can be made for the soil out side the excavation as for the soil inside Compare an expanding cylinder radius with a block of thickness Line af NEZ 2 a C E Rigid boundary a outside the excavation Poisson s ratios of the cylinder and the block are Vc and Vb respectively The displacements d are therefore Cylinder d E d 1 vp These are equal when 1 a Note In the Safe version of Frew v 0 3 and if the soil is undrained take 0 5 Oasys Ltd 2014 ws Frew Oasys GEO Suite for Windows 8 7 3 8 8 Therefore for an undrained soil using the Safe model the distance to the external rigid boundary t 1 5 0 91 1 65 radius of the actual excavation Stiffness Varying with Depth The analysis for axi symmetric problems assumes that Young s modulus remains constant to great depth In practice it usually increases with depth and the material becomes relatively rigid at a finite depth It is not obvious how this will affect the formulae given above but a comparison of Frew with a finite element run of Safe carried out for th
113. ilure mechanisms involving both local and overall failure are checked It is considered that this system provides a good approximation to limits which are both necessary and sufficient Limits for soils with cohesion and pore water pressure The same arguments for redistribution may be followed through for both active and passive limits for soils with cohesion c pore water pressure and effective wall pressure p where p p Between any two depths 2 Z 0x 2 lt Z the limits may be expressed as active 2 dc cK dz lt j lt j A 1 lt p dz lt N E6 passive i Z uj u ydz pg cK 2 ej ej E7 A further restriction is placed so that negative effective stresses are never used or implied This is achieved by substituting zero for negative values of the expressions in brackets in the above inequalities In the passive pressure limit calculation it is generally not reasonable to impose the internal failure mechanism implied by Equation E7 The program therefore only enforces the limit implied by Equation E2 which states that the earth pressure integrated between the surface and depth z must not exceed the Rankine passive pressure integrated over the same depth If Equation E7 indicates a failure however a small is included in the output table and the user must check that an internal failure me
114. imations used in the Mindlin method For both methods if the Generate option is used an approximate modification is made to allow for the irregular variation of E value with depth If the Specified option is selected then the user must define the required profile Redistribution of Pressures The use of redistribution can allow for the effects of arching in the soil If no redistribution is specified the wall pressures at all points are limited to lie between and Dp However if redistribution is allowed it is assumed that arching may take place according to theory presented in Calculation of Active and Passive Limits and Application of Redistribution Note It is considered that the redistribution option while being less conservative is more realistic Minimum Equivalent Fluid Pressure If it is required that the total active pressure on the wall at any depth below the ground surface should not drop below a specified value a Minimum Equivalent Fluid Pressure MEFP can be automatically calculated by Frew To use this feature check the minimum equivalent fluid pressure box on the Analysis Data dialog This will add an option to the Stage Operations which allows entry of MEFP parameters The MEFP option is available on the Analysis option dialog box Note These parameters can be changed for each stage lf the MEFP is checked then another option is added to the Stage Operations tree view for that stage called Minimum
115. inue to check the output carefully to ensure the assumptions and adjustments to characteristic values are as they require Note that pore pressures and strut pre stress are not factored If a strut pre stress is used to model a structural force and other effects of actions are being factored the user may wish to factor the input value of strut pre stress Oasys Ltd 2014 input a8 Seismic Model 1 fwd Partial Factors Select Partial Factors to use EE otes 3 Soil strength Direct BD 42 00 factors for permanent works design have been quoted Code Direct Kp Partial Factors E be oe User defined values with other assumptions made in the model e g unplanned excavation ground water conditions Right factor 10 surcharges Harten Reference to the appropriate code Factors for material properties should be made tan useful summary of design assumptions for each method is n presented in CIRIA C580 Cu Left factor Documents and cases 1 0 E Factors for Effects of Actions Apply partial factor on effects of actions Partial factor value 1 35 Soil strength Partial Factors can only be applied if automatic calculation of earth pressure coefficients is selected for all materials see Material properties Note When soil strength factors are selected the direct Kp Partial Factors can not be selected and are set to 1 0 User defined values are a set of soil strength P
116. ion of work done due to unit load acting on two elastic soil blocks with Young s modulus profile E The following expression has been developed for the coefficient acting at node i D a Ez eu dz E T zz D s ee az z where 5 is the displacement at depth 2 of the elastic soil block with Young s modulus profile E due to unit load at node i No rigorous theoretical justification for this expression is available However comparison between finite element solutions and those produced by this approximation have been carried out and have shown that for most practical situations errors will rarely exceed 20 The following figure shows one of the more severe cases that could be envisaged Pappin et al 1985 Oasys Ltd 2014 Detailed Processes in Frew 8 2 4 E YOUNGS MODULUS MAT DISPLACEMENT min EM E m 150 of F DEPTH meters DEPTH imaers Comparison of Safe and Mindlin flexibility approximations with FEA at three depths Here the displacement of the elastic soil block with Young s modulus profile E due to unit load at three different levels is shown compared against rigorous finite element solutions Effect of the Distance to Vertical Rigid Boundaries Vertical rigid boundaries may occur in the ground near a retaining wall due to unusual geological or man made features More often the effect of a vertical boundary is required to model
117. isting Frew data is validated If there are any warnings or errors they are displayed in the wizard Warnings can be ignored but the data cannot be exported if there are any errors If the relevant checkbox on this page is checked a log file which contains all the errors and warnings during the export process will be created Oasys Ltd 2014 Frew Oasys GEO Suite for Windows Frew Safe Link Pre export checks Materials WARMING Angle of Friction back calculated For Material 1 From values of Ka and Please verify the computed value WARNING Poisson s ratio back calculated For Material 1 From values of Kr Please verify the computed value WARNING Angle of Friction back calculated For Material 2 From values of Ka and Kp Please verify the computed value WARNING Poisson s ratio back calculated for Material 2 From values of Kr Please verify the computed value Boundary distances Override left and right boundary distances Original data Corrected Distance From the wall to the left rigid boundary 20 00 20 00 Distance From the wall the right rigid boundary m 20 00 20 00 The user may also specify different boundary distances than those input in the actual file This is particularly useful in cases when large vertical boundary distances from wall have been specified For further information see Accuracy of modelling boundaries in Frew If there are no errors the Next button will open the nex
118. l d is consistent with the groundwater profile and Uf is balanced at the base Note This modification to water profile is only for stability calculations It is NOT carried over to the actual Frew analysis 2 2 Full Analysis The analysis is carried out in steps corresponding to the proposed stages of excavation and construction An example showing typical stages of construction that can be modelled is given in Assembling Data The initial stage Stage 0 is used to calculate the soil stress prior to the installation of the wall Displacements computed in this stage are set to zero At each stage thereafter the incremental displacements due to the changes caused by that stage are calculated and added to the existing displacements The soil stresses strut forces wall bending moments and shear forces are then determined The numerical representation is shown below Wall Soil to left of wall VERTICAL RIGID BOUND ARY VERTICAL RIGID BOUNDARY RIGID BASE The wall is modelled as a series of elastic beam elements joined at the nodes The lowest node is either the base of the wall or at a prescribed rigid base in the ground beneath the wall Oasys Ltd 2014 Methods of Analysis 12 The soil at each side of the wall is connected at the nodes as shown on the figure At each stage of construction the analysis comprises the following steps a The initial earth pressures and the out of balance nodal forces are calculate
119. l of rotation strut Generally speaking the centrelines of the actual surcharge and the equivalent surcharge coincide However if the extent of equivalent surcharge crosses the wall then the equivalent surcharge is assumed to have the same width calculated as above but it is assumed to start from the edge of the wall Note The partial factors for user defined surcharges are not applied to the equivalent surcharge due to overburden above the lowest strut in this analysis of multi propped walls Oasys Ltd 2014 Methods of Analysis 2 1 3 Active and Passive Limits Active and passive pressures are calculated at the top and base level of each stratum and at intermediate levels These are placed where there is a change in linear profile of pressure with depth The generation of intermediate levels ensures the accuracy of the calculation of bending moments and shear forces Intermediate levels will be generated where there is a change in the linear profile of pressure with depth e g at water table levels piezometric points at surcharge levels at intervals of 0 5 units within a stratum with a cohesion strength component The effective active and passive pressures are denoted by p and respectively These calculated from the following equations K Koc where effective cohesion undrained strength as appropriate vertical effective overburden pressure Note Modification of the
120. le Stage B Switch to Drained parameters Displacement mm F9 50 29 29 50 75 55 m 45 40 35 2125 D 125 25D 375 Pressure kPa 30375 250 Scale 1 300 STAGE 4 Soil Strength Parameters ta Drained Stage C Revert to Drained PWP Profile Oasys Ltd 2014 Detailed Processes in Frew 158 Displacement mm 75 50 25 0 25 50 75 55 50 E NE 45 EL ral 35 30375 250 125 0 125 250 375 Pressure kPa Scale 1 300 STAGE 5 PWP to drained profile List of References References British Standards Institute 2004 A1 2013 Design of Structures for Earthquake Resistance Part 1 General rules seismic actions and rules for buildings BS EN 1998 1 2004 A1 2013 British Standards Institute 2004 Design of Structures for Earthquake Resistance Part 5 Foundations retaining structures and geotechnical aspects BS EN 1998 5 2004 British Standards Institute 2011 Recommendations for the design of structures subject to traffic loading to BS EN 1997 1 2004 Published Document PD6694 1 201 1 Broms B B 1972 Stability of flexible structures General Report 5th Euro Conf SMFE Vol 2 Madrid Mononobe N and Matsuo M 1929 On the determination of earth pressures during earthquakes Proceedings of the World Engineering Congress Vol 9 179 187 1929 Okabe S 1926 General theory of earth pressure Journal of the Japanese Society of Civil Engineers
121. lem from beginning to end to ensure that the correct parameters entered as global data see Assembling Data Note Tables are locked for editing in the program when results are available To edit the data in the tables the user has to explicitly delete the results 3 4 1 Titles When a existing file is opened or a new file created without the New Model Wizard the first window to appear is the Titles window 2 FREWman fwd Titles m EJ Job Number Initials Last Edit D ate Bitmap Job Title OASy S Sotware Development Subtitle FRE Validation FREY Manual Example Calc Heading General Example Written Frew version 18 2 Drained amp Undrained Conditions Wall amp Strut Helaxatian This window allows entry of identification data for each program file The following fields are available Oasys Ltd 2014 33 Frew Oasys GEO Suite for Windows Job Number allows entry of an identifying job number The user can view previously used job numbers by clicking the drop down button Initials for entry of the users initials Date this field is set by the program at the date the file is saved Job Title allows a single line for entry of the job title Subtitle allows a single line of additional job or calculation information Calculation Heading allows a single line for the main calculation heading The titles are reproduced in the title block at the head of all printed information for the c
122. luvioglacial Sands Fluvioglacial Sands Fluviaglacial Sands Fluvioglacial Sands Fluvioglacial Sands 1 Place the cursor over the first node and select with the left button 2 Hold down the Shift key 3 Place the cursor over the last node still holding down the Shift key and select the area of nodes with the left button Oasys Ltd 2014 59 Frew Oasys GEO Suite for Windows 3 5 9 1 To designate the soil zones 1 Place the cursor to the left or right of the wall as required 2 Click the right button on the mouse This will activate the zones box Soil Zones Select the required soil from the combo box and select OK Note The number of the soil comes from the list of material types created in the materials table see Material Properties Air or water are designated as material type O Editing soil zones Once entered the soil zones can be edited using either of the methods given above Dig Fill Operations When using automatic node generation to specify excavation or backfill click the button on the toolbar Right clicking on the left or right side of the wall in the graphical input view will bring up the Dig Fill dialog level level m 25 Enter the required new ground level and click OK If the new ground level is above the existing ground level i e filling the uppermost material will be extended to the new ground level When using manual node generation e
123. mall the diagram will become triangular This pressure distribution is then used to modify the active pressure limit Comparison of this distribution with the parametric studies suggests that it is generally conservative Variation of K with depth If varies with depth it is considered conservative to choose a mean value of 2 between any depth z and the level of the surcharge and then impose the criteria that the active force due to the surcharge down to depth z be equal to the force derived from the above diagram This is then subjected to the further limitation that the pressure never exceeds qK at any depth where is the active pressure coefficient at depth z Oasys Lid 2014 135 Frew Oasys GEO Suite for Windows 8 5 2 Passive Pressures Due to Strip Load Surcharges Frew calculates the increase in passive pressure due to a uniformly distributed load udl but can not make an allowance for strip load surcharges The program assumes that the passive pressure at depth z is equal to 2c K where o is the vertical effective stress at depth z set equal to U 0 O udi is the sum of vertical pressure of all udl surcharges specified above z Kae malls When there is wall friction P For strip load surcharges the user must adjust K by adding additional soil layers if necessary to allow for any increase in the passive pressure This could be done using a series of trial failu
124. n be understood by studying the stress path plot below Failure in an undrained material occurs at the intersection of the and lines This point is derived from the effective stress parameters of the material number for effective stress parameters specified by the user for each undrained material The envelope of possible total stress values is shown in red examples for shape factors of 1 and 0 75 are shown this is taken to be elliptical except where reduced by shape factors gt 0 The calculated undrained effective stress path is shown in blue For each iteration in an undrained stage the program calculates the total stress and the effective stress using the value on the blue effective stress path unless limited by the red envelope The undrained pore pressure is then the difference between the total and effective stresses The diagram shows that if the shape factor is less than 1 it is possible for the effective stress calculated to lie outside the limits of the effective stress parameters this would lead to some changes in total stress and hence displacement in the transition from undrained to effective stress behaviour This problem is avoided by following the recommendation to use the default shape factor of 1 0 Advice on data pore pressures when using this feature Any pore pressures entered by the user will be ignored in an undrained material for which automatic calculation of pore pressures has been requested i e by se
125. n can be switched on or off by choosing Print Selection from the File menu or the filter button d At the beginning of each stage s results any surcharge or strut insertion or removal will be noted and the progress of convergence through the iterations is shown in a table After the final stage s results an additional table shows the envelope of the calculated displacement bending moment and shear force values at each node Lines of output can be highlighted and then copied to the clipboard and pasted into most Windows applications as shown below The output can also be directly exported to various text or HTML formats by selecting Export from the File menu The results table is quite wide so the default font size is condensed If larger size print is required this can be set by clicking the Larger Font 4 putton on the toolbar Note that the Page Setup may need to be landscape to avoid the lines of the results table scrolling on to two lines STAGE 9 WALL amp STRUT RELAXATION RESULTS FOR STAGE 9 Wall amp Strut Relaxation Surcharge or strut changes Strut no 3 removed at this stage Strut no 4 removed at this stage Strut no 5 inserted at this stage Strut no 6 inserted at this stage Calculation details E Profiles assumed for calculation generated On the LEFT at ground level 38000 E at bottom node 53000 kN m On the RIGHT E at ground level 39000 E at bottom node 58000 kN m Iter Inc Node
126. n entering material data the user can choose to enter a granular or cohesive material Where the granular option is chosen the material parameters are calculated as described in Appendix A of PD6694 1 The user is required to enter suitable stiffness curves Rf g vs D H and passive pressure Kp vs D H curves The Seed and ldriss 1970 curve for small strain stiffness of granular soils with 9096 densification as shown in Appendix A of PD6694 1 is included as a standard curve for the calculation of small strain stiffness S amp l 90 Densification and this may be used if appropriate Likewise there is an inbuilt option for Kp v D H Standard 6N 6P that calculates the Kp value using the formula shown in section 9 4 3 of PD6694 1 Where the cohesive option is chosen the material parameters specified in the materials table are used directly in the integral bridge analysis Oasys Ltd 2014 Frew Oasys GEO Suite for Windows 5 2 Algorithms The following algorithm outlines the steps involved in integral bridge analysis in Frew START Analyse in front or behind wall Behind dl Infront D H values are assumed at front of wall D H values are assumed at back of wall Material parameters Material parameters calculated from D H values calculated from D H values Initial summer expansion Initial winter contraction Reset to Winter contraction Summer expansion Reset to original struts original struts and sta
127. n to any general limitations of the method there are a number of points that the user should be aware of when using the Mononobe Okabe method in Frew These points should be considered and it should be confirmed that the assumptions made are valid for the model being assessed Frew only considers the active case where the soil stress along the face of the wall is at pressures greater than this then the loads generated will not be correct Because Frew uses the vertical effective stress to calculate the dynamic soil force the calculated force will be affected by any surface loads applied to the soil Frew only considers vertical walls i e it uses a value of 90 for w Where partial factors are applied factored values of and 6 will be used Oasys Ltd 2014 Seismic Analysis 100 6 2 4 Load Application Methods There are two options relating to how the seismic loading is applied to the retaining wall The first is for the load to be distributed across the face of the wall Where the load is distributed it is applied as a strut load to each node along the retained soil i e a strut is created with stiffness of O and a prestress equal to the required force and is applied to the relevant node First the average pressure on the back of the retaining wall is calculated as _ _ 1 The load at each node is then calculated The load distribution is assumed to be linear and can be set by specifying the of the average l
128. nchors can be installed at any node at any stage during the analysis Aa strut Prestress Ps stiffness 55 Angle i J aver arm Ls Modes As shown above the struts are specified as having a prestress force Ps and a stiffness Ss in terms of force unit displacement A lever arm Ls and inclination s can also be specified to model the effect of a moment being applied to the wall by a strut or anchor This feature can be used to model the effect of an inclined strut or anchor applying the force eccentrically to the wall section If s is set 90Deg it can also be used to model a moment restraint and an applied moment Based on the geometry defined above the force and moment M applied at the node by the strut is given by P P 55 cos a 65 1 cosa sina G5 2 2 M P L sina S L cosa SING OSL s sina G6 In these expressions d is the horizontal deflection of the node and q the rotation of the node since the introduction of the strut These equations can be written in the form of matrices that represented all struts currently acting on the wall as P P I5 6 15 2119 G7 P L sina S o S n A Oasys Ltd 2014 Detailed Processes in Frew 142 where the strut stiffness matrices diagonal and equal to S S cos a G9 5 S L sina 010 5 1 S L sita G11 The ef
129. o be dry and to have a unit weight of 20 kN m and at rest coefficient of earth pressure 1 0 For an excavation of 5m the change in horizontal stress is calculated as 5 20 K 100K therefore at some depth d below the top of the wall the initial horizontal stress in the front of the wall will be p 20d 100K For d gt 5m For the test problem Poisson s ratio 0 3 and 0 3 1 0 3 0 43 therefore p 7 20d 43 kN m Due to digging 5m the wall moves and the stresses in front of the wall increases to The change in stress is therefore defined as AP Frew Po Summary of Results The ratio of AP Frew AP sate is shown below for the two cases considered Oasys Lid 2014 121 Frew Oasys GEO Suite for Windows Constant Youngs modulus of 40 OOOkM ma Frew 5 14 1 2 1 4 0 2 g L D 0 25 PUn LBS 0 4 a ee b x M e 0 8 Linearly increasing Youngs modulus with 10 depth 5000 at ground level Increasing at SDDIOEN m2 depth IS SNOWS NOW varies WI eptn an e an average This sh how A Safe Vari ith depth and the ratio L D Taki ti Oasys Ltd 2014 Detailed Processes in Frew 122 throughout the depth of soil the variation shown below is obtained 1 5 Constant Young s a modulus Linearly incre asini Young s modulus with
130. oad at the base Frew will then calculate the corresponding load at the top of the wall to ensure the the total load is unchanged The force applied at each node is taken as the sum of the pressure as described above from the mid point of the element below to the mid point of the element above the node Two example distributions are shown below one with 100 average load at the base of the wall i e constant pressure and one with 50 of the average pressure at the base of the wall i e 0 5q at the base to 1 5q at the top Where the load is applied as a point load a strut force will be generated and applied at the elevation specified by the user If nodes are generated automatically this will be taken into account when generating nodes to ensure that a node is present at the correct level Oasys Ltd 2014 Frew Oasys GEO Suite for Windows 6 2 5 Groundwater Loading Where pervious soils are specified by the user the dynamic load from groundwater Ewd is calculated as 12 hYw For which Kh is the horizontal seismic coefficient w the unit weight of water and H the height of the water table from the base of the wall If load application is specified as a point load then the load is applied as a point load at a level of f x H from the base of the wall where the factor is specified by the user If the load application is specified as a distributed load then it is applied as a pressure increasingly linea
131. of the wall as required 50 00 0 00 500000 10 49 00 45 00 500000 10 500000 10 Nore Glacial Till Undrained Mone Glacial Till Undrained None Glacial Till Undrained None 47 00 46 00 500000 10 500000 10 Glacial Till Undrained None Glacial Till LIndrained 45 00 500000 10 500000 10 Glacial Till Undrained Glacial Till Undrained None Mone 38300 500000 10 500000 10 Glacial Till Undrained Glacial Till Undrained Nore Mone S00000 10 500000 1 0 Glacial Till Undrainied Mane Glacial Till Undrained Glacial Till Undrained S00000 10 500000 10 Glacial Till Undrained Glacial Till Urdrained Fluvioglacial Sands Till Li ndrained S00000 10 00000 10 Fluvioglacial Sands Glacial Till rdrained Fluvioglacial Sands Fluvioglacial 5 ands S00000 10 FOO000 10 Fluvioglacial Sands Fluvioglacial 5 ands Fluvioglacial Sands Fluviaglacial Sands 500000 10 0 00 Fluvioglacial Sands Fluvioglacial Sands Fluviaglacial Sands Fluvioglacial 5 ands 0 00 0 00 Fluvioglacial Sands Fluvioglacial Sands Fluviaglacial Sands Fluviaglacial Sands 0 00 0 00 Fluvioglacial Sands Fluvioglacial Sands Fluvioglacial Sands Fluviaglacial Sands Place the curso
132. of units may be set by selecting any of the buttons SI KN m kip ft or kip in Once the correct units have been selected then click OK to continue SI units have been used as the default standard throughout this document 3 4 3 Material Properties The properties for the different layers of materials either side of the wall are entered in tabular form Properties must be entered for all the materials which will be required for all construction stages drained and undrained parameters of the same material type are to be used then each set of parameters must be entered on a separate line Note The user should understand the way Frew models undrained and drained behaviour and the transition between the two For further information see the section on Total and Effective Stress Brief descriptions for each of the material types can be entered here This description is used when assigning material types to either side of the wall thereby creating the soil zones see entering Soil Zones Note Material type O represents air or water no additional input data is required by the user Oasys Ltd 2014 35 Frew Oasys GEO Suite for Windows Material Description Property EO Young s modulus given as Earth Press Coef Cw C Ka Kp Kac 1 A general constant parameter for the layer as a whole or 2 A specific value for a given reference level yO Unit weight defined as the bulk unit weight y Coefficient of ea
133. oftware product Select to generate the mesh Existing settings are Mesh bias Lett 1 2 3 2 5 1 I aximum number of elements per horizontal segment Lett Right J J 6 10 2 1 See the Help for a discussion on how to use these settings This dialog allows the user to bias the mesh along horizontal segments as desired The biased segments have more nodes towards the wall The horizontal segments correspond to horizontal lines running from the left boundary to right boundary A horizontal segment typically joins points located at the boundary with a point on the wall or any surcharge points two surcharge points etc The user can also specify the maximum number of elements that can be generated along a horizontal segment This option may help the user to increase the number of elements if necessary The default value is 6 However this does not affect the number of elements generated along the wall width which is always 2 Then the required Gwa file is created The data from this file can be imported into the Safe file by clicking Import Gwa menu button in the Safe program Oasys Ltd 2014 Frew Safe Link Edit View Data Run Data Analysis Combinations Queues Window Help Mew Open Close Save Save Save Run 1 Save in ald Format Print Setup Export 2 Import wA History Version 1 C TesEs FREWman sfd 2 Tests JFREW man Safet sfd 3 Ci Tests
134. on the boxes and E to open or close the tree diagram for each stage Accessing data using Gateway The user can also access the Global Data menu items and the current stage menu items using the Gateway Whenever the data item in the current stage item is different from the previous stage it is shown in bold 3 1 Assembling Data Each problem should be sub divided into a series of construction Stages commencing with the initial stage referred to by Frew as Stage This stage defines the situation prior to the wall being installed in the ground and is therefore specified in terms of drained parameters Various operations can be performed in subsequent stages including changes from drained to undrained and vice versa Oasys Ltd 2014 25 Frew Oasys GEO Suite for Windows Sketches showing the wall soil strata surcharges water pressure strut and excavation levels should be prepared for each Stage Examples of potential changes that can be applied during the construction stages are Stage 0 Set up initial stresses in the soil by adding the material types groundwater conditions and applying any surcharges required prior to installing the wall All materials should be set to drained parameters for this stage Stage 1 Install wall Change to undrained materials if required In this example undrained pore pressures are calculated by the program see Undrained Materials and Calculated Pore Pressures Subsequent Excav
135. or Use in Memos Letters etc Frew is a program used to analyse the behaviour of flexible retaining walls It predicts the displacement shear forces and bending moments of the wall and the earth pressures each side of the wall resulting from a series of actions These actions include excavation filling dewatering changing soil or wall properties and applying or removing struts anchors or surcharges The program models the soil as an elastic continuum and allows for soil failure by restricting the earth pressures to lie within the active or passive limits and also includes the effect of arching Brief Description for Inclusion in Reports The following pages contain a summary of the analysis method used by Frew It is intended that they can be copied and included with calculations or reports as the need arises Frew is a program to analyse the soil structure interaction problem of a flexible retaining wall for example a sheet pile or diaphragm wall The wall is represented as a line of nodal points and three stiffness matrices relating nodal forces to displacements are developed represents the wall in bending and the others represent the soil on each side of the wall The soil behaviour is modelled using one of three methods 1 Safe flexibility method the soil is represented as an elastic solid with the soil Stiffness matrices being developed from pre stored stiffness matrices calculated using the Oasys Ltd 2014 Brief Tec
136. possible however to have zero pressure at a point with 2 2 coincident it is admissible to have very small hole in a wall supporting sand Pressure REPE o P A If 2 Z is a finite length sand would flow out because of the self weight of the material between 2 Z there is another limiting line indicated as P in the above figure For depth z below 2 this limit is given by pcs Zi However there is also a more severe restriction This occurs because at depth 2 there must be non zero vertical stress since the horizontal stress immediately above 2 IS gt D In order to maintain this horizontal stress the minimum vertical stress is approximately D Thus for points below 7 the line D provides limit gt az KP Po 2 E4 Equations E2 and E3 are similar in form to D 2 D was argued in Application in Frew above that p 2 was sufficient but not necessary whilst Equation E2 was necessary but not sufficient Similarly Equation E4 is not necessary By analogy with Equation E2 the necessary Equation becomes Oasys Lid 2014 131 Frew Oasys GEO Suite for Windows gt pode dz Kp dz zi lt i 52 5 When the redistribution option is specified in Frew Equation is enforced between all pairs of nodes corresponding to depths 2 and 24 Z gt 2 In effect this means that a large number of possible fa
137. r over the first node and select with the left button 2 Click the right button on the mouse This will activate the zones box Wall El values El value for selected nodes kMm m Enter the wall stiffness in the box and select OK Editing wall stiffness Oasys Ltd 2014 input Data 62 The wall stiffness can be changed either 1 repeating the procedure above to overwrite the entered data or 2 by selecting the required node in the table using the cursor and typing in a new number Note The Wall stiffness extends to the top of the node below The last node in the added list is therefore not available in the wall window to prevent the wall being extended below the base of the defined problem 3 5 11 Groundwater The profile of groundwater can be either hydrostatic or piezometric These can be different on either side of the wall For a hydrostatic distribution enter a single piezometer with zero pressure at the phreatic surface The profile of pressure with depth will be linear beneath this level and have a gradient dependent on the specified unit weight of water Note The specified unit weight of water is a single global value which is applied to all piezometers on the same side of the wall The piezometric distribution is specified using a series of pressure heads The water pressure at any point is computed by interpolating vertically between two adjacent points Note The highest specified point
138. r removal of struts or surcharges for each stage Strut no 1 inserted at this stage Surcharge no 1 applied at this stage Calculation details E profiles used in the calculation Progress through iterations showing maximum incremental node displacement displacement error and pressure error and where they occur Ground levels front and back for each stage Profile down all nodes of e Displacement e Vertical total and effective stress V and e Horizontal total and effective stress P e Water Pressure U e Bending Moment e Shear Force Oasys Ltd 2014 Note For the undrained condition if undrained pore pressures are not calculated by the program the values of Ve and Pe shown and the user s U value will be apparent effective stresses and pore pressures rather than actual stresses and pore pressures A note will be added to the foot of the results table and the values shown in brackets See Undrained materials for more background 7 2 21 Results Annotations and Error Messages Indicator symbols will be added to the results table if the soil pressure limits are being exceeded These are as follows Indicator Meaning A The effective earth pressure is less than 1 01 times the active limit but within the convergence pressure limit P The effective earth pressure is greater than 0 99 times the passive limit but within the convergence pressure limit The effective earth pressure is outside the converg
139. r the Gateway The following provides details of the available graphics options Fie Edit Mur Stage data Analysis Graphics Window Help Toolbar Status Gateway Tabular Output Oasys Ltd 2014 Graphics FREWman fwd Graphical Output Total Stress Passive Limit Active Limit 400 0 Scale x 1 235 y 1 188 Pressure Im STAGE 5 Excavate to Level 40 5mOD amp Dewater Graphical toolbar buttons Axis 5 a reference grid behind the drawing Set Scale This allows the user to toggle between the default best fit scale the closest available engineering scale e g 1 200 1 250 1 500 1 1000 1 1250 1 2500 or exact scaling The same options are available via the View menu Set exact scale command Oasys Ltd 2014 111 Frew Oasys GEO Suite for Windows Save Metafile allows the file to be saved in the format of a Windows Metafile This retains the viewed scale The metafile can be imported into other programs such as word processors spreadsheets and drawing packages Copy allows the view to be copied to the clipboard in the form of a Windows Metafile Zoom Facility Select an area to zoom in to by using the mouse to click on a point on the drawing and then dragging the box outwards to select the area to be viewed The program will automatically scale the new
140. ram defaults A time interval may be set to save data files automatically Automatic saving can be disabled if required by clearing the Save file check box Show Welcome Screen enables or disables the display of the Welcome Screen The Welcome Screen will appear on program start up and give the option for the user to create a new file to open an existing file by browsing or to open a recently used file Begin new files using the New Model Wizard if ticked will lead the user through a series of screens to enter basic data for a new file For more details see New Model Wizard Company Info allows the user to change the company name and logo on the top of each page of print out To add a bitmap enter the full path of the file The bitmap will appear fitted into a space approximately 4cm by 1cm The aspect ratio will be maintained For internal Arup versions of the program the bitmap option is not available Page Setup opens a dialog which allows the user to specify the calculation sheet style for graphical and text printing e g whether it has borders and a company logo Oasys Ltd 2014 input Data 9 3 3 New Model Wizard The New Model Wizard is accessed by selecting the File New Ctrl N option from the main menu or by clicking the New button on the Frew toolbar The New Model Wizard is designed to ensure that some basic settings and global data can be easily entered It does not create an entire data file and strut
141. re surfaces to determine the passive pressure at any location Alternatively the user should check through and calculate the following requirements detailed here to derive the most suitable increase in the passive pressures Requirement 1 General passive wedge Requirement 2 Check of the depth of the influence of the load Requirement 3 For a uniform surcharge Requirement 4 General application Note The problem becomes more difficult if K varies with depth A simple expedient would be to use equations specified in Requirement 4 with the appropriate value of K at each depth This can be unsafe however if a soil with high K overlies a soil with low Requirement 1 which me qb Ks limits the total passive force effect to could be volated for the less frictional soil Oasys Ltd 2014 Detailed Processes in Frew 136 8 5 2 1 Requirement 1 General passive wedge pa 4 Calculation Consider a deep failure plane which will encompass the whole area of the strip load surcharge The following calculation assumes no wall friction Assume that this is generally valid even with wall friction Calculate the weight of the wedge W 1 T 1 W y d tan 4 2 3 Say the passive force due to the weight of the wedge is 1 172 K WAK Thus if W is increased by the effect of the surcharge qB the passive force will increase by qBAK
142. reasonably regular close intervals down the line of the wall and beyond to the base of the problem This allows the program to clearly model the flexibility of the wall and provide results of the forces pressures and bending moments which are given at each node location Note As a guide it is recommended that the maximum separation between any two nodes must never be greater than twice the minimum separation between any of the nodes Frew gives a warning if this rule is violated Frew may have difficulty if unusually short stiff elements are used To obtain equilibrium bending moments are obtained from the calculated curvature second differential of displacement This requires that for any three consecutive nodes curvature can be derived to sufficient accuracy from displacements which are computed to six significant figures This becomes difficult for short stiff elements especially if they displace by large amounts e g at the top of a flexible wall Note Material properties must be defined before the program allows the node locations to be selected Defining the depth of the problem If the correct level range is not shown on the graphical view define the extent of the problem by selecting the menu option Graphics Scaling Set Problem limits and then enter the maximum and minimum levels of the nodes Oasys Ltd 2014 input 4 Problem Range amp Snap Interval Problem range amp snap interval E Graphics
143. relate to features which are not required for the current analysis and can be ignored for example NOTE Missing material for effective stress params in undrained pore pressure calcs is only relevant if undrained pore pressure calculations are required If no errors are found then the calculation continues through each stage To continue to analysis when there are data warnings click the Proceed button 2 FREWman fwd Solution Progress Checking data OF Analysing for stage Iteration Inc Max Node Displacement Node Pressure Made number displacement number error number eror number mm mm NOTE Missing material for effective stress params In undrained pore pressure cales ignore if not using feature Proceed Note The Tabular Output view will be shown once the calculations have been completed It can also be accessed View Tabular Output as shown below or the item in the Gateway Oasys Ltd 2014 7 2 Fie Edit Mur Global data Stage data Analysis Graphics Window Help Toolbar w Status Gateway Graphical Output Tabular Cutput Tabulated Output Tabulated output is available from the View menu the Gateway or the Frew toolbar Two tabs are available for the tabular view by default the summary tab is shown that shows the key results and input data however all data and available results are printed when selecting the full tab results output The items show
144. ric pressure profile specified on passive side to create submerged excavation otage 3 Stage A New pore water pressure profile calculated by user for undrained conditions otage 4 Stage B Changed to drained parameters otage 5 Stage C Pore water pressure to drained profile Calculation procedure In this example it is assumed that Au 2 Oasys Ltd 2014 153 Frew Oasys GEO Suite for Windows Note Users should be aware that as 5 used to calculate in stage 0 total horizontal stress in this stage should be calculated by adding to Po In any other undrained stage are used and are equal to 1 therefore total horizontal stress can be calculated by simply adding u to P e Pore water Pressure Calculations Active Pressures STAGE 0 PARAMETERS 2 3 4 5 3 m 7 X 07 eo ca Effective wg Effect Fe User spec Total Pe YE 18 36 54 63 106 10 20 a 40 50 1 24 23 4n 5b b4 1b 24 32 45 56 fu 1 Tal 196 216 234 25 4 x Bu 104 112 120 126 156 144 152 104 117 120 128 136 144 152 130 140 150 160 170 190 190 E 2 49 A Ab 45 44 43 42 4 40 3g 20 dr 3b 35 24 33 32 12 ie 14 15 1b 1 16 13 20 E 242
145. ritical slip surface a result which is nearly sufficient to ensure a conservative solution is found Oasys Ltd 2014 Detailed Processes in Frew 18 8 4 2 Application in Frew In Frew elasticity methods are used to derive a pressure distribution on the wall and this is then modified so that forces on sections of the wall are approximately within the limits required by plastic strength considerations Active limit for a dry cohesionless soil The method used will first be described for dry cohesionless soil considering only the active limit For a uniform material values of the coefficient of active earth pressure K 2 have been derived by various researchers by searching for critical failure surfaces These give necessary limits of the forces on the wall PES o Strictly where the minimum effective soil force on the wall between the free surface and depth z y effective unit weight of soil Only if it is assumed that the earth pressure increases linearly with depth is it valid to use the same value of the equation for wall pressure Now define p K y 2 in a uniform soil Or K v dz 0 in a non uniform soil Let earth pressure at depth z p Then provided the value of is very good upper bound the condition D 2p at all depths E1 will be sufficient safe but not necessary since the necessary condition only considers force Oasys Ltd 2014 Frew O
146. rly from 0 at the water table to the maximum pressure p at the base max 7 Pmax J Where there are multiple strata present with some specified as pervious and others as impervious the pressure profile is the same as that described above but with zero pressure applied along the length of the wall adjacent to impervious soils Output Analysis and Data Checking For a stability check to check or set a wall toe level select Stability Check from the Analysis menu the button or the Stability Check button on the Node Generation Data dialog Oasys Ltd 2014 File Edit View Globaldata Stage data Analysis Tools Window Help 32 9 ad Stability Check f Analyse a x eL For full analysis select Analyse from the Analysis menu or the gt button Stability Check A dialog will appear with default parameters for the stability check The list of stages in the program for which the stability check will be carried out will be listed in a table Stability check B C D Stage Failure Rotation Balance water mechanis strut index pressure Defaults Fixed YES Fixed Eart Free Eart Free Free Ear Na Free Ear Ha Free Ear Ma E Default calculation interval m Iteration limit Select the required collapse mechanism for details see Stability Check For the free earth method the lowest strut is selected as the rotation strut If au
147. rth pressure at rest i e horizontal effective stress vertical effective stress Select from the drop down list whether the earth pressure coefficients will be Calculated or User Specified see Calculation of earth pressure coefficients Note For Calculated the cells of Ka Kp Kac and Kap will be uneditable and when values are entered into 6 and Cw c the earth pressure coefficients will be calculated For User Specified the cells for 09 0 Cw c will be greyed out and the cells of Ka Kp Kac and Kap will be editable Unit weight defined as the bulk unit weight y Angle of internal friction Ratio of wall soil friction angle to shearing resistance angle Angle of ground surface to horizontal in degrees ACTIVE Ratio of wall adhesion to soil cohesion Active earth pressure with allowance for soil wall friction Passive earth pressure with allowance for soil wall friction Active earth pressure due to cohesion K 14S C if Cw 0 or Oasys Ltd 2014 Kpc Kr yO gradient E gradient Drained Undrained Shape factor Material no for effective stress parameters Oasys Ltd 2014 input Data Passive earth pressure due to cohesion 27 2 Kp if Cw 0 Or Ratio of change in horizontal effective stress to a unit change in vertical effective stress i e v 1 v where v Poisson s ratio see Eff
148. ry and only the initial conditions of the Frew model in the Safe model 3 Export whole model If the user selects this option almost the whole data barring some unsupported features which will be detailed later will be exported to Safe The user is further provided three choices to export groundwater data 1 Export no groundwater data In this case groundwater data is completely suppressed during the export process Oasys Lid 2014 Frew Oasys GEO Suite for Windows 2 Export complete groundwater data In this case the whole groundwater data from all the stages is exported 3 Export selective stages If this option is chosen the user has to specify the comma separated list of stages for which the groundwater data must be exported This option may be used for excluding stages involving transition from undrained behaviour to drained behaviour In Frew the user has to calculate these transient pore pressures himself However in Safe different approaches can be adopted for calculating the transient pore pressures There may be cases when the user calculate transient pore pressure data in Frew may not accurately model the problem in Safe In such situations the user may want to filter out groundwater data from certain stages On clicking Finish the following Mesh Settings dialog pops up if the user chooses Export only first stage data or Export whole model options Mesh settings Mesh generation uses a third party s
149. s Calculate the actual change in pore water pressure due to movement in the wall between the two stages This demands an understanding of the undrained stress path For soils which are at yield in shear Skempton s pore pressure parameter A would be useful if its value can be assessed lf the soils have not reached yield a modified value of A is required Au BAo A Ao Ao Skempton s equation In stiff clays it may be assumed that the mean normal effective stress remains constant during shearing This assumption would not necessarily be appropriate to other soils and should always be carefully In the plane strain conditions of Frew it amounts to Au Ao 2 Add AU values to the user input values of u at stage 0 Input this adjusted u value into the Frew analysis Three additional stages A B and C are now required to complete the transition between undrained and drained behaviour Stage A The new pore pressure profile should now be introduced into the next stage without changing the undrained strength criteria of the soils and keeping Kr 1 This causes Frew to recalculate effective stresses but total stresses are unchanged and no movement occurs Stage B The soil strength parameters should then be changed to drained values Oasys Ltd 2014 Detailed Processes in Frew 152 retaining the undrained pore pressures This provides a check as if the above procedure has been carried o
150. s and vertical arching within the soil governs the stress field Furthermore when the strength of the soil is fully mobilised in active and passive wedges deformations are again localised and the geometry in plan is not too important However situations can arise in which the plan geometry has a very significant effect on the magnitude of the movements This is the case in heavily overconsolidated clays for which the movements may be large before the strength is fully mobilised As explained above the effect is particularly important in computing movements before the first props are inserted 8 7 1 SoilInside the Excavation Consider a cylinder of soil radius a inside a circular excavation Consider the simplified case in which Young s Modulus E is constant with depth and the depth is large To determine the horizontal stiffness compare this with a block of thickness t and the same Young s Modulus E Line af a t F 4 4 Rigid Block of boundary inside 94 excavation Lubricated Surface at equilvalent centre Let the Poisson s ratios of the cylinder and the block be vc and vb respectively For the same pressure p the displacements d are Cylinder d P E pt Block dec cb The displacements are equal when 1 v A 1 Oasys Ltd 2014 Detailed Processes in Frew Note In the Safe version of Frew vb 0 3 and
151. s full extent Further discussion of the methods can be found in Pappin et al 1985 Approximations Used in the Safe Method The Safe method uses a matrix of predetermined flexibility coefficients to represent the flexibility of the ground The stiffness of the soil is then represented by inverting this flexibility matrix The predetermined coefficients were generated using the finite element program Safe The Basic Safe Model The flexibility coefficients stored in Frew were determined from a series of finite element analyses carried out using the Safe program Free Surface a il v 0 3 ww Height 101 elements ub Length L 10 H unequal elements Rough Rigid Boundaries The above figure shows the geometry and boundary conditions assumed for the mesh in the Safe analysis The mesh is divided into 101 elements in height The length is 10 times the total mesh height and is divided into a series of unequal elements which increase in length away from the left hand boundary AB A 0 5 1 5 2 5 3 5 dr 99 5 219 5 B 100 Oasys Ltd 2014 Detailed Processes in Frew The model acts in plane strain and the vertical free face AB represents the location of the retaining wall in Frew The boundary is divded into 101 elements as shown A unit force was applied to each element in turn distributed as a uniform pressure over the length of the element The horizontal displacement a
152. s r a teal aleae au duda 123 8 3 Approximations Used in the Mindlin 123 8 3 1 The Basic Mindlin 123 8 3 2 Application of the Model in FTeW 124 8 3 2 1 Accuracy of the Mindlin Solution Frew uo irc opt eto ER M dS 124 8 4 Calculation of Active and Passive Limits and Application of Redistribution 126 SAT General M EE MUS 127 96 42 Applicatiohi In 128 5 4 9 Iterative Technique Adopted In Frew octo ronis Rei tuii en cn ail e i a KR eR IR s 132 8 5 Active Pressures Due to Strip Load Surcharges 133 8 5 1 Application in ROW cecidi CREE CE c unu nac uus cre iir etia d i Ed ERE Fa REGN UR 133 8 5 2 Passive Pressures Due to Strip Load Surcharges esee eeeseee eese ener nnnm nnn 135 8 5 2 1 le fif TTE 136 95 222 P
153. sed to derive horizontal stresses in the ground The pressures therefore on a rigid ideally frictionless vertical boundary would be double the Boussinesq values Oasys Ltd 2014 input Data 46 strip Load onstant value of E with depth 2 For the case where the stiffness E increases sharply at a depth less than the width of the surcharge the load will appear to the more flexible soil to act rather like a For the stiffer soil the effect of the surcharge load will still appear as the Boussinesq pressure Strip Load i Sharp increase in E BB BEB ee LI For both cases the analysis calculates the change of pressure on the wall before further movement using the equation p 2 where phB the change of horizontal stress according to the Boussinesq equations K 5 correction factor specified by the user Where Young s modulus is constant with Oasys Ltd 2014 Frew Oasys GEO Suite for Windows depth Ks should be taken as 1 0 For the case where stiffness increases sharply K can have a large range of values the evaluation of which is beyond the scope of this text However if the strip load is wide compared with its distance from the wall and the depth of the deforming soil a value of K V 1 v will give results equivalent to loading with a udl with K v 1 v Active and Passive
154. sidered to be reasonable when the width of the wall W is large relative to the depth or to the distance to the vertical boundary Oasys Ltd 2014 Frew Oasys GEO Suite for Windows Line af symmetry Soil surface X Y plane 7 A a Vertical rigid plar T boundary Plane of retaining wall lt Additianal nodes to fix Additional nodes vertical boundary to fix rigid base When W is small three dimensional effects will dominate and to approximate the fixity of a plane by a single line of nodes becomes somewhat dubious Additional nodes on the fixed planes away from the plane of symmetry X X Z Z or varying the width W of the loaded rectangle at the fixed nodes would improve this approximation Nevertheless using the Mindlin flexibility method provides an approximate means of studying the importance of W A drawback of the Mindlin flexibility method is that Young s modulus is assumed to be constant with depth This is significantly different from the Safe flexibility method which can model accurately a linearly increasing modulus with depth Nevertheless the same ratios that are applied to model modulus variations can still be used with the Mindlin method see Irregular variation of E An example comparing flexibility coefficients is given below Pappin et al 1985 Oasys Ltd 2014 Detailed Processes in Frew 1 YOUNGS MODULUS DISPLACEMENT min EM E m 150 of F DEPT
155. solved For either problem several struts with specified forces can be applied Note The user should be aware that other mechanisms of collapse may exist for the problem which are not considered by the stability check These include rotation of the soil mass failure of the props anchors or failure of the wall in bending Fixed Earth Mechanisms This method is used to model cantilever walls The mechanism assumes that the wall is fixed by a passive force developing near its base The level of the base of the wall is calculated to give equilibrium under this assumed pressure distribution Oasys Ltd 2014 5 Frew Oasys GEO Suite for Windows 2 1 2 1 D eflected shape at limit of equilibrium Active pressures Passive pressures Passive pressures Active pressures Pressure diagram for Fixed Earth mechanism Free Earth Mechanisms This method is used to model propped walls The mechanism assumes rotation about a specified strut and calculates the level of the base of the wall and the force in the strut required to give equilibrium Strut E Deflected shape at limit of equilibrium Active pressures Passive pressures Pressure diagram for Free Earth mechanism Multi propped walls When the model has more than one active strut the lowest strut is taken as the rotation strut by the program The following assumptions and approximations are made e The ground level on th
156. sor before typing the amendments as required Oasys Ltd 2014 55 Frew Oasys GEO Suite for Windows 3 5 7 3 5 8 Stage 0 Initial condition Stage 1 Insert Wall in Undrained Conditions Stage 2 Apply Plant Loading on Active Side and E Stage 3 Apply Anchor Prestress Stage 4 Apply Anchor Stiffness Stage b Excavate ta Final Level 40 5m00 amp Dew Stage Apply Roof amp Basement Slab Struts amp Hen Stage 7 Undrained to Dirained i is Stage amp Undrained to Dirained Switch Soil Param Stage 9 Undrained to Drained PMP to drained P Stage 10 Remove Plant Loading Stage 11 Wall amp Strut Relaxation lt Apply Remove Surcharges Surcharges can be applied and removed individually for each stage Edit the Stage In Out entries as required in the table FREWman_V19 1 fwd e NEN Surcharge nes Cc Side ES s E Type ES Reus EC Partial Factor iss EN Wis zm Defaults 1 2 1 50 00 HDL 10 00 T 2 Right 40 00 UCL 15 00 1 00 3 i Lett 35 00 Strip 18 00 1 20 5 00 3 00 0 30 A o a Insert Remove Struts Struts can be inserted and removed individually for each stage Edit the Stage In Out entries as required in the table FREWman fwd Struts Strut 3a P ben ate am number 7m KN m comam 200 00 0 00 40 00 0 50 0 00 2000 00 40 00 0 00 40000 00
157. ss Wall friction should be allowed for in selecting values of ka and kp Undrained behaviour can be represented by setting ka and kp to unity with appropriate values of c kac and Kpc The use of redistribution can allow for the effects of arching in the soil If no redistribution is specified the wall pressures at all points are limited to lie between pa and pp However if redistribution is allowed it is assumed that arching may take place according to theory presented in Calculation of Active and Passive Limits and Application of Redistribution Note It is considered that the redistribution option while still being somewhat conservative Oasys Ltd 2014 Methods of Analysis represents the real behaviour much more accurately lf surcharges of limited extent are specified above the level in question the active pressure is increased in accordance with the theory presented in Active Pressures due to Strip Load Surcharges However strip surcharges are not included in calculating passive pressure see Passive Pressures due to Strip Load Surcharges 2 4 1 Effects of Excavation and Backfill Excavation backfill or changes of pore pressure cause a change in vertical effective stress It is assumed that in the absence of wall movement the change in horizontal effective stress will be given by Aoh KrAov For an isotropic elastic material Kr 2 v 1 v where V Poisson s ratio for drained
158. sults e g on the passive side of the wall During analysis the active pressure is set to a minimum of a ygy b where y is the level of the node If this is the governing criterion on active pressure an symbol is shown in the tabular output In the graphical output the MEFP derived pressure is just plotted as part of the normal active pressure line 3 5 12 8 Passive Softening This analysis option can be specified for individual stages If passive softening is used then the undrained shear strength of the material is assumed to increase linearly from zero to the global softening value over the passive softening depth entered To use this option enter e The depth to which surface softening occurs distance units he magnitude of original strength stiffness to be used for global softening 96 The strength of all undrained material below a softening depth will be reduced to global softening 96 of the value in the Material Properties table Note Since either or both sides of the wall can be excavated the user can specify separate parameters for both sides of the wall Oasys Ltd 2014 input Data Undrained shear strength CO Tm T referenced at YO Gradient of undrained shear Soil 1 strength Excavation level Soil 3 undrained Depth to softening level Global softening 90 Soil 2 Global softening 100 Soil 4 drained Wall 3 5 13 Convergence Control The following parameters
159. surcharge and stage data should be entered once the wizard is complete Cancelling at any time will result in an empty document Note The New Model Wizard can only be accessed if the Begin new files using New Model Wizard check box in Tools Preferences is checked 3 3 1 New Model Wizard Titles and Units The first property page of the New Model Wizard is the Titles and Units window The following fields are available Job Number allows entry of an identifying job number The user can view previously used job numbers by clicking the drop down button Initials for entry of the users initials Date this field is set by the program at the date the file is saved Job Title allows a single line for entry of the job title Subtitle allows a single line of additional job or calculation information Calculation Heading allows a single line for the main calculation heading The titles are reproduced in the title block at the head of all printed information for the calculations The fields should therefore be used to provide as many details as possible to identify the individual calculation runs An additional field for notes has also been included to allow the entry of a detailed description of the calculation This can be reproduced at the start of the data output by selection of notes using File Print Selection Clicking the Units button opens the standard units dialog 3 3 2 New Model Wizard Basic Data The second wizard page
160. t Selection dialog Choose Tabular or Graphical and the required data and or results to show Enter the required stage list All is the default but individual stages can entered separated by spaces or ranges of stage e g 2 to 5 Print 5election Tabular C2 Graphical Print For stage list All Select the tems to print Surcharges Geometry Struts 5011 Properties Stage Changes Results Deselect all S elect all Print 5election Tabular Graphical Print For stage list All Select the tems to print Displacement Shear Force Earth Pressures Envelope Bending Moment Deselect all Select all For tabular output the output view will be opened or updated with only the selected output shown The information can be sent to printer in the usual way For graphical output the Print dialog will be opened allowing selection of a suitable printer Note Graphical output can not currently be batch printed to PDF printer drivers a warning message will be generated in this case To print to PDF open the graphical and print each stage individually Oasys Lid 2014 113 Frew Oasys GEO Suite for Windows 8 8 1 8 2 8 2 1 Detailed Processes in Frew General This section provides a detailed description of the assumptions and calculation methods carried out by Frew It is important to gain a good understanding of these methods in order to be able to use and interpret the program to it
161. t all nodes in the middle of the side of each element was then calculated down the vertical free face AB These displacements represent the flexibility coefficients and were stored as the flexibility matrix Using the principle of superposition the total horizontal displacement at all nodes due to any load combination can be estimated Two cases are considered one with the nodes on the line AB free to move vertically and the other with the nodes fixed vertically These are referred to as the Fixed and Free cases respectively For each case there are two sets of flexibility coefficients stored within Frew These apply to soils having either e aconstant Young s modulus E e ora Young s modulus which increases linearly with depth from zero at the surface For varying profiles of E the user can specify their best estimate of a linear profile to best describe the variation with level The program will combine and modify the matrices to accommodate this see Accuracy with respect to Young s modulus E Alternatively the program will select a linear profile of Young s modulus based on the specified non linear profile the program then applies further corrections as described in Irregular variation of E 8 2 2 Application of the Model in Frew Scaling factors are used to map the flexibility matrices from the Safe model onto the user defined model in Frew To carry out this mapping the boundary is divided into Frew elements
162. t data Oasys Lid 2014 Frew Oasys GEO Suite for Windows 22 1 Nodal Springs Spring constants kM per m Safel Node Loads 4 2 6 Materials In Frew material data is specified only for Soil strata In the Safe model the excavations are represented using void material the wall is modeled using a linear elastic material and the soil is modeled using Mohr Coulomb materials Safe void material data zz Safel Water or air properties Seles o Description 1 MU 2 2 a a a a a aee l S i EF Hj The wall material data is supplied by the user during the export process Oasys Ltd 2014 Frew Safe Link Safe1 Linear elastic material properties lE A B seroma ay pue B UT 1 007 03 The material model has all the data required for Safe Mohr Coulomb model except for the angle of friction 2 and Poisson s ratio v Frew material data zz Frew Manual fwd Materials L ES ss esr eet K EO Unit Earth Phi Delta m eta Cw Drained erial no uL Description kN m weight pressure je eclive stress kN 7m coefficient ratio ratio
163. t of shear stresses on the plane of the wall in response to vertical displacements of the wall and soil which are largely related to non elastic movements 3 5 12 5 Young s Modulus E The value of Young s modulus is given to each soil layer see Material Properties The profile of Young s modulus may therefore vary irregularly with depth Best fit linear 7 prafile Ez Irregular profile of Young s modulus with depth Ez However a linear profile is needed in order to use the Safe and constant value of E to use the Mindlin method Oasys Lid 2014 Frew Oasys GEO Suite for Windows 3 5 12 6 3 5 12 7 Safe Model When using the Safe Model Frew can generate a best fit linear profile through the stepped profile created by the individual soil layers on either side of the wall Alternatively the user can specify profile by giving the value of Young s modulus at the lowest node and then a gradient of the line positive gradient creates an increasing profile with depth When Frew generates the best fit line it then makes further modifications to the stiffness matrix This attempts to fit the irregular profile of Young s modulus better For details on the Accuracy with respect to Young s modulus E Mindlin Model The Mindlin Model requires a constant value of E The method can either generate a best fit value or use a user specified value For details on the use of E in the Mindlin method see Approx
164. t page of the wizard where the wall data should be entered This includes the wall thickness density Young s modulus and Poisson s ratio for the wall material Oasys Ltd 2014 Frew Safe Link Frew Safe Link Wall properties Young s modulus MPa Poisson s ratio 1 3 thickness Wall density 20 EM rn Export options CO Export geometry and restraints only Prior to mesh generation Export only First stage data Export whole model Groundwater data Do not export groundwater data gt Export complete ground water data CO Export groundwater data For the follwing stages Enter comma separated list of stage indices The following three options are provided for exporting data 1 Export geometry and restraints only If this option is selected only the critical points lines and areas are exported together with the boundary conditions at the ends of the model No mesh generation data is exported Thus data pertaining to surcharges struts etc which are dependent on the mesh data are also not exported This option is useful if the user wants to add additional geometric entities in the model after importing into Safe data file 2 Export only first stage data This option enables the user to export the entire first stage data including mesh generation data surcharges struts etc to Safe This is useful if the user is interested in replicating the same geomet
165. tages unless otherwise amended On completion of Stage 0 new stages can be added or inserted to the list The number of the current stage is always displayed in the status line at the base of the main window For Help press F1 Cell A 1 1 INUM Stage 0 2 Current stage number for Pd active window 3 5 2 New Stages New stages can be added to the list by selecting Add Stage on the Stage Operations window This activates a New Stage Title box Mew Stage Title Enter tithe for new stage pO Inserting after Stage Oasys Lid 2014 53 Frew Oasys GEO Suite for Windows 3 5 3 3 5 4 3 5 5 The stage title is then entered and the number of the stage before the new stage Once the OK button is selected the new stage is added Note The number that first appears in the Inserting after Stage window is the number of the stage currently highlighted by the cursor Inserting Stages Select the Add stage button on the stage operations tree diagram and follow the instructions as for new stages Deleting a Stage otages can be deleted by highlighting the stage title in the Stage Operation window and selecting Delete stage A check box will appear before the stage is deleted A Delete stage 7 Cancel Editing Stage Data It is possible to step through the stages in order to access and edit the same data window for each stage Use the buttons on the tool bar to move up and down between the vario
166. ter approximation 4 For the soil beneath the berm calculate amended Kp and c value as follows e choose various levels below the berm eg points i etc e ati determine critical failure surface C by using method of wedges or using Oasys SLOPE to give minimum passive force Fi If straight line wedges are used the wall friction should normally be set to zero in this process e calculate passive pressure Pi between base of berm at level Zb and point i at level Zi as p F Fa 2 where ga is the passive force within the height of the berm Oasys Ltd 2014 147 Frew Oasys GEO Suite for Windows h F K yt 2c K de 0 which for a dry berm SE ee JK h determine equivalent and Ci such that Oy 2 Ki where Uj is the average pore pressure between points b and i O vi is the average vertical effective stress see Total and Effective Stress between point b and i yh o zuat 7 2 Z Z U where is the sum of all uniformly distributed surcharges above point i usually none present in this case e determine critical failure surface D to give minimum passive force F e calculate passive pressure between point i and point at level 2 pi F F z 2 e determine equivalent C such that 2 e continue down wall to base of problem e redefine soil zones and soil properties with et
167. the appropriate level on the graphical and clicking the mouse button This opens the piezometer data box Water data Level Pressure LI rit weight of water This allows the level of the piezometer to be confirmed or edited and the corresponding pressure to be entered The pressure P is given as Oasys Lid 2014 6 Frew Oasys GEO Suite for Windows Ie A Yy where level of the piezometer h p h level of the piezometric head at the piezometer Y Global unit weight of water Note Any amendments to the global weight of water will automatically be applied to all piezometers on the same side of the wall Editing Once the information for a piezometer has been entered then the data can be edited or deleted using the tabulated information beside the graphical view The piezometers can also be deleted by placing the cursor over the location and clicking the left button whilst holding down the Shift key 3 5 12 Analysis Data The analysis data dialog allows specification of the following overall parameters required to define the problem Note These parameters can be changed for each stage Oasys Ltd 2014 input Data 66 20515 Seismic fwd Analysis data Analysis methad Boundary distances m e SAFE Mindlin LEFT 50 RIGHT 50 interface Young s modulus Free Fixed Specified Generated Wall relaxation Youngs modulus data LEFT
168. the effects of the surcharge on the soil stresses before installation of the wall In some cases this may however prevent the program from converging as there is a discontinuity in the lateral earth pressures at the top node Where this occurs this can usually be worked around by applying the surcharge at a level slightly below the ground surface 3 4 6 1 Application of Uniformly Distributed Loads To determine the elastic effect on the horizontal effective stress udl surcharges are multiplied by in Stage 0 whereas in later stages they are multiplied by K They are therefore treated in the same way as the weight of soil both in the initial state Stage O and in later stages as excavation and filling takes place see Effects of excavation and backfill In all stages including Stage 0 strip surcharges are multiplied by the factor Ks described above Active and passive limit pressures are also modified using the values of for each layer beneath the udl 3 4 6 2 Application of Strip Loads For strip loads the change in stress in elastic conditions is difficult to determine because the horizontal stress is extremely sensitive to the variation with depth of the soil stiffness and to anisotropy of the soil stiffness Two extremes have therefore been considered 1 Forthe case where the Young s modulus E for the soil is constant for a depth several times greater than the width of the surcharge the Boussinesq equations may be u
169. these points is specified in the Analysis Options For the Front and Back of the wall e Active and passive pressures e Pore water pressure and material layer number he Bending moment and shear force profiles down the wall If the Balance water pressures feature is switched on see Analysis and Data Checking two sets of results will be shown the original results with the water data input by the user and the final results obtained by the program after balancing the water pressure at the base of the wall Oasys Ltd 2014 107 Frew Oasys GEO Suite for Windows 7 2 2 Detailed Results The output provides detailed results for all stages FREWman fwd Output 5 INITIAL DATA Notes e S011 Types Multi Propped Wall Drained 5 Undrained Conditions Wall 4 Strut Relaxation Soil properties Unit Epc Earth prezzure m coefficients 20 00 1 000 1 000 2 000 2 000 1 000 User Specified 21 00 0 150 5 500 000 000 0 250 User Specified 20 00 200 4 500 000 000 0 300 User Specified cu Gradient EU Gradient Drained of c of E EM 1 EN fm run EHM m EN fm rm Undrained 36 00 50 00 2 00 60000 0 100 00 Undrained 00 50 00 00 50000 0 50 00 00 50 00 00 40000 0 65 00 Drained Surcharge properties Nn Stage Side Level Pressure Offset thdth In Out m kH m m m Z 11 Left 50 00 10 00 ti Listing of additions o
170. this ratio may be either cumulative values starting from zero stress and zero strain or incremental values Tangent madulus incremental Stress Secant modulus cumulative Strain The above shows these two possibilities for a point X on a non linear stress strain curve The modulus in terms of cumulative stress and strain is commonly referred to as a secant modulus whilst the modulus related to a small increment of stress and strain at point Xis a tangent modulus Note It is also possible to have an incremental secant modulus which approximates to the tangent modulus for small increments In describing the change of stiffness from short term to long term as a change of stiffness modulus structural engineers are referring to secant moduli But it is important to realise that Frew uses tangent incremental moduli as its basic data This means that merely changing stiffness moduli when nothing else is changed will have no effect at alll Changing From Short Term to Long Term Stiffness The following shows the type of stress strain Curve required for a change from short term to long term Stiffness Oasys Ltd 2014 Detailed Processes in Frew 150 E D J E Creep optem a Relaxation s on gi B 099 Strain E Creep and relaxation The high short term stiffness on OA is required to drop to the lower long term stiffness on line OBC Consider an element of structure which in the
171. thods Oasys Ltd 2014 3 Frew Oasys GEO Suite for Windows e Soil pressure limits active and passive may be redistributed to allow for arching effects e vertical distribution of Young s modulus may be specified and each model provides an approximate representation of this distribution Alternatively the user may specify Young s modulus as either constant for the Mindlin model or linearly variable for the Safe method if desired e The effect of summer expansion and winter contraction of integral bridges can be assessed using the integral bridge feature e Where appropriate the effect of seismic ground movement can be assessed using the Wood s and Mononobe Okabe methods 1 3 Components of the User Interface The principal components of Frew s user interface are the Gateway Table Views Graphical Output Tabular Output toolbars menus and input dialogs These are illustrated below Standard Toolbar Frew Toolbar Graphics Toolbar Frew 19 1 Frew ample fwd gs Units and Preferences Global Material properties 2 Node levels 15 Strut properties 4 Surcharges 1 Partial factors Data for Stage 0 Apply remove surcharges 30 00 uu 1 23 00 Material 1 28 00 Matena 1 27 20 Material 1 26 50 Material 1 25 80 Malena 1 struts 25 00 Malena 1 Soil zones 2420 Malena 1 Water data 23 40 Malena 2 Left 97 22 60 Material 2 Righif1 21 80 Malena 2 Analysis method 21 00 M
172. tic Mohr Coulomb PL STRN n8 37 58 3 i 4 Stage Material 4 Elastic Mahr Caulomb 5 5h Material 5 Elastic Maohr Coulomb FL STRN P amp Stage Material Elastic Mahr Caulomb L STRH 7 vod Waterco Void PLSTRN 1e 005 B wal S O Oasys Ltd 2014 Frew Oasys GEO Suite for Windows 4 2 7 Groundwater Frew and Safe use different approaches for modeling pore pressure distribution Following are a couple of important differences Piecewise linear interpolation of pore Radius of influence approach pressure All soil zone materials share the same pore Each material has its own pore pressure pressure distribution data distribution In Safe each data point is characterized by pore pressure value its gradient and a radius of influence The net pore pressure at a given point is the weighted average of the pore pressures calculated at the given point using the existing pore pressure data points The weights for points which lie within a square defined by this radius of influence the weights are typically much higher compared to the weights for the points located outside the square In Frew we can have different pore pressure gradients above and below a particular pore pressure data point However this situation is not possible in Safe for a given data point as only a single pore pressure gradient is specified In or
173. tions of and stresses within the structure through a specified sequence of construction This sequence usually involves the initial installation of the wall followed by a series of activities such as variations of soil levels and water pressures the insertion or removal of struts or ground anchors and the application of surcharges The program calculates displacements earth pressures bending moments shear forces and strut or anchor forces occurring during each stage in construction It is important to realise that Frew is an advanced program analysing a complex problem and the user must be fully aware of the various methods of analysis requirements and limitations discussed in this help file before use The program input is fully interactive and allows both experienced and inexperienced users to control the program operation 1 2 Program Features The main features of Frew are summarised below e The geometry of the wall is specified by a number of nodes The positions of these nodes are expressed by reduced levels The nodes can be generated from the other data soil interface levels etc using the Automatic Node Generation feature Oasys Ltd 2014 About Frew Wall Sail to left of wall VERTICAL RIGID BOUNDARY VERTICAL RIGID BOUNDARY RIGID BASE e Wall stiffness is constant between nodes but may change at nodes The base of the wall may be specified at any node nodes below this are in free soil The wall
174. tomatic node generation is being used ticking the Generate nodes box will create all required nodes for the Frew analysis on successful completion of the stability check for at least a single stage The program initially uses the default calculation interval in the stability calculations If the stability Oasys Lid 2014 103 Frew Oasys GEO Suite for Windows calculations are not successful with the initial calculation interval the program will appropriately change the value of the calculation interval and re run the stability check This process is repeated at most three times Tip If the stability check fails to find the toe depth within the specified number of iterations try increasing the calculation interval or the iteration limit Full Analysis The program carries out data checks as follows 1 The wall is continuous i e does not contain any holes 2 The soil is continuous beneath the surface 3 The node spacing is reasonably uniform in order to prevent any mathematical instability in the calculations 4 All essential data has been entered e g wall plan length and global Poisson s ratio for the Mindlin method boundary distances for the Safe and Mindlin methods 5 Nodes have been generated or specified If there are errors these must be corrected before the analysis can continue Any data warnings will also be shown here These should be reviewed and any required changes made Sometimes these warnings will
175. tting a valid material for effective stress parameters in the Materials table Oasys Ltd 2014 Methods of Analysis Warning messages These appear as symbols in the node results tables for any stage which calculates undrained pore pressures and a brief explanation is added in a footnote to the table s initial stress outside effective strength limits This situation should not occur and probably reflects a data error in which either the user has change the effective stress parameters between stages or in the first stage inconsistent values of K K and K have been specified It could possibly be detected on returning to use of effective stress parameters after an undrained stage with FACTOR 1 undrained strength unreasonably low for stress state At an earlier drained stage probably at initialisation the program has calculated a horizontal stress which exceeds the undrained strength limits specified by the user in relation to the vertical stress at the node This may be due to incorrect data i e undrained strength not increasing in a sensible manner with depth or too low a value of constant C Told R Sess Ecurdrg Ch eed ce dred m Boandrg purse Ch el I tec 2 on on LLI LE en LE LLI c on MEAN STRESS Py Ph pe or Pu Ph Je
176. urface plane A Vertical rigid plar boundary Flane of retaining wall Additional nodes ta fix Additional nodes vertical boundary to fix rigid base Half Space representation of a soil block When modelling each side of the wall the soil must still be considered as a half space and the resulting flexibility matrix doubled Therefore to maintain symmetry at the plane of the wall additional nodes must be added to both sides The base nodes are restrained both vertically Z Z direction and horizontally X X whereas the vertical boundary nodes are only restrained horizontally As these nodes are on a plane of symmetry X X Z Z they will not move in the Y Y direction restraints are achieved by modelling stresses acting on rectangular areas centred at each boundary node to force the displacements of the boundary nodes to be zero For a vertical boundary node a horizontal pressure is considered to act on a vertical rectangle For a base node two stresses are considered one being a horizontal traction and the other a vertical pressure both acting on a horizontal rectangle In all cases the width of the rectangle is taken as being equal to the width W specified for the wall The final soil stiffness matrix has been computed by eliminating the boundary nodes and inverting the flexibility matrix of the central nodes only Accuracy of the Mindlin Solution in Frew This method of modelling fixity is con
177. us stages E 4 The number of each stage is displayed on the status line at the base main window Editing Stage 2 lt Once the correct stage has been reached edit the data as normal To reach specific windows go to the Stage Operations tree diagram highlight the required operation at the required stage and then either e double click on the highlighted operation or e select the Change this stage button to open the window Oasys Ltd 2014 input Data sa 2 FREWman fwd Stage Operations Stage 2 Apply Plant Loading an Act Ma change Stage 3 Apply Anchor Prestress Stage 4 Apply Anchor Stiffness Stage Excavate to Final Level 40 5 Stage amp Apply Roof amp Basement Slab Stage Undrained ta Drained PP amp pply remove surcharges 3 Inzert remawve struts Soil zones Delete stage wall data Add stage Analysis method Mew stage will be added Convergence control after the current stage as aa shown on the Status bar Meo ee Meet Note Changes made in a stage will be copied through to subsequent stages until the program encounters a specific change already made by the user For example changing the soil zones in an early stage will update later stages which had the same soil zone specification 3 5 6 Editing Stage Titles The stage titles can be edited by left clicking on the title so that it becomes highlighted in yellow and then clicking again to get the cur
178. ut correctly this step should have no effect and could be omitted However movement will occur if the specified pore pressures and effective strength parameters are not consistent with the computed horizontal effective stresses Since the horizontal stresses are consistent with the undrained strengths this would imply inconsistency between the specified pore pressures drained and undrained strengths In more complex analyses it is possible that assumptions made in the above process may cause small amounts of movement to occur in Stage B If this occurs the user should review the modelling of the problem and the strength criteria to ensure that results are reasonable 9 Stage C Finally the pore pressure profile should be changed to its long term drained values with Kr lt 1 as for drained behaviour This will cause changes in horizontal total stresses and movement will be needed to restore equilibrium 8 10 1 Undrained to Drained Examples The following proudes an example of a manually applied transition between undrained and drained materials Soil Properties Soil EO Unit Ka Kp Kpc Kr cO YO Gradient kPa wt kPa m KN ms cE Undrd 50000 18 1 0 1 00 1 0 2 00 2 00 1 00 100 500 10 2000 Draine 35000 18 1 0 0 15 7 0 0 0 0 25 0 50 0 0 2000 d Stage Data otage 0 Initial drained conditions with PWP specified otage 1 Undrained materials and excavation to 48 5m OD otage 2 Excavation to 42 5m OD insert strut 1 piezomet
179. value at the free surface It is found that very good results are obtained by dividing this profile into two components 1 constant with depth 2 linearly increasing from zero The stiffness matrices for the two components are then added theoretical proof of this result has been found 8 2 3 2 Irregular Variation of E Linear variation of stiffness with depth can oversimplify the design profile An approximate method of adjusting the matrices to accommodate irregular variations of soil stiffness has been determined empirically and consists of the following Best fit linear profile Ez Irregular profile of Young s modulus with depth Ez This method calculates a best fit linear Young s modulus profile to represent the actual variation E Z Oasys Ltd 2014 117 Frew Oasys GEO Suite for Windows Application of matrix The flexibility matrix F corresponding to the linear approximation can then be derived from the pre calculated matrices as described in The Basic Safe Model In order to adjust this matrix to obtain the flexibility matrix F corresponding to the actual variation of Young s modulus each term in row i of F is multiplied by a coefficient To maintain symmetry terms F and F are both multiplied by the same coefficient chosen as the smaller of A or number of alternative means of deriving coefficient have been attempted based on consideration of the different distribut
180. xcavation is specified by changing the material to the required side of one or more nodes to O This represents air or water Backfilling is specified by Oasys Ltd 2014 Input Data changing the material from O to the required material number for the backfill material Digging and backfilling can be carried out on either side of the wall Any dig fill operations are carried forward to successive stages until they are changed Note It is not permissible to dig to or below the base of the wall However this could be modelled if required by specifying a very low bending stiffness for the bottom section of the wall 3 5 10 Wall Data Wall data must be entered in Stage 1 and be specified for all subsequent stages As stages are added the previous stage data is copied The wall can be of uniform or non uniform stiffness profile which can be changed for each stage Any revised stiffness will be then be carried forward and used for all subsequent stages until it is changed again Note Changes in wall stiffness between stages will not adjust the moment curvature relationship that exists at the end of the previous stage The use of wall relaxation must be used to adjust the moment curvature relationship For automatic node generation the top level and bending stiffness of the wall is specified in the Wall Data table Changes in bending stiffness down the wall can be specified by entering more than one line in this table The base of

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