Home

Triaxial - Geocomp

1. What you do next depends on your estimate of how close the strain is to failure If you are certain that the strain is a lot less than strain at failure you can open the Load Control window type in the Load value you recorded and click Go When the load has been applied unlock the piston bring down the Run menu and select Restart If there is reason to believe that the strain is close to the failure condition you should abort the test and test another sample with the higher capacity load cell VII 10 Q Can I run any stress path with this system A This system allows specification of all steps required to perform a triaxial stress path test along any stress path possible in a triaxial cell see diagram below including the ability to specify changes in pore pressure We can for example follow the stress path for an element in the upstream slope of a dam as pore water pressure builds up to the steady state seepage value In this case the total stresses stay constant but pore pressure is built up over time To the best of our knowledge our system is the only system in the world that can do this We include the ability to consolidate along prescribed stress paths before and after backpressure saturation This is important for materials where you want to limit the amount of swell you permit during the backpressure saturation phase Data can be collected at specified times specified displacements or specified strains as either incremental v
2. Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING O 2013 Geocomp Corp A Your expectation is correct It should start to level off and then continue to go down gradually Two possibilities for your result are that the sample had a tendency to swell or the sample was subjected to an excessively high effective stress by mistake prior to the consolidation phase which would result in the sample rebounding Il 8 Q We are in the process of running some tests with the triaxial set up believe we are having an issue with the consolidation phase Why do the consolidation curves seem strange Consolidation Phase 0 04 0 03 aiii NM oe LU LLL EERS LLL LLL LO 9 os LLL LLL LLL LEE TERR IR Et ous oT LTE 001 A N AUAN 0 02 oos AHAA T woa OOOO T I er LLL oos OTAU EEE EE EEE 0 200 400 600 800 1000 1200 1400 Strain Time min A Unless you are running Ko consolidation the sample is being squeezed in both vertical and horizontal directions during the consolidation phase Therefore you must use volumetric NOT vertical strain when analyzing your results The curves from above should now look like Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp Consolidation Phase i E THEE TTL HE i HEA Se EET s 200 400 600 800 1000 1200 1400 I Time min Ill GENERAL Ill 1 Q At the b
3. which is the inverse of the compressibility cP cr K V In the equation P is pressure and V is volume The bulk modulus thus measures the response in pressure due to a change in relative volume essentially measuring the substance s resistance to uniform compression Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp The bulk modulus is related to the Young s modulus E and the shear modulus G through the equation below Oo A 3 3G E Typical Young s Modulus and Shear Modulus values for various soil types are shown in the following published tables EM1110 1 1904 Engineering and Design Settlement Analysis by Army Corps Eng Very soft clay 500 4800 CLAY 2 9 Advanced Soil Mechanics by B M Das 02 04 Medium dense sand 0 25 0 4 03 045 Silty sand 0 2 0 4 Sand and gravel 0 15 M 0 35 v 0 254 0 0025 x PI where PI Plasticity index Wroth 1975 Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp Design applications of raft foundations by J A Hemsley Soil Type Short term Long term Loading Sand S The TRIAXIAL program runs a K consolidation by forcing zero lateral strain i e keeping the area constant throughout the consolidation phase This is done by equating the vertical strain to the volumetri
4. generated from data dumped into a file after the test Note that the time scale is not the same for the different soil types When possible the target load pressure should be reached in less than 0 5 min Consequently a high P Gain setting is good for very soft soils It is easy to reach the target load pressure value for stiff soils However as seen in the last two graphs the target value may not be reached smoothly To help this situation the l Gain or both the I Gain and P Gain can be decreased Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp Very Soft Soil Modulus 2790 psi PID 0 5 1 0 PID 5 1 0 Medium Soil Modulus 4000 psi BEER EEE m IE tE das ma ns nmn nx nudo um ux am Oe an tE DD nz ax AS Da t nu Time ni nj Time mi nj Stiff Soil Modulus 10 000 psi PID 0 3 1 0 PID 5 1 0 Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp In addition a rule of thumb for response time is given in Section 6 0 of ASTM standard D2435 Standard Test Methods for One Dimensional Consolidation Properties of Soils Using Incremantal Loading Load application generally should be completed in a time corresponding to 0 01 t100 or less For soils where primary consolidation is completed in 3 min load application should be less
5. thereafter at every 1 Take sufficient readings to define the stress strain curve hence more frequent readings may be required in the early stages of the test and as failure is approached Continue the loading to 15 strain except loading may be stopped when the principal stress difference deviator stress has dropped 20 or when 5 additional axial strain occurs after a peak in principal stress difference deviator stress Therefore you could delete the extraneous data points past the peak or after 15 strain is reached ll 6 Q The consolidation phase of a CIUC test that am running is taking over 2 days The sample does not seem to ever consolidate See the attached Test Graph window am testing a 70 mm 2 8 in diameter silty clay sample Any ideas or comments as to why it is taking so long Am I doing something wrong Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp Horizontal Stress 51 986 psi Vertical Stress 51 972 psi Sample Pressure 32 003 psi Effective Horizontal Stress E 9 983 psi Effective Vertical Stress E 9 969 psi Axial Strain o 87208 Volumetric Strain E 9 287 Cell Volume Change E 2332 cc Sample Volume Change E 15 91 cc Time to End of Step 801 14 14 Step Elapsed Time E 22 46 44 Test Elapsed Time 2 00 20 45 Close Help Ko Gain 1U1 Ko Pressure Limit 14 35 2 4a 60 SQRT of TIME
6. 3 As you turn each back on immediately press the ESC key on the keypad to reset everything back to the imbedded controller default values 4 Now go to your LoadTrac ll and FlowTrac Il hardware manuals In Section 2 1 4 of each manual Setup section you will find a table of default settings for your system Got through each LCD menu and be sure the settings on the menu agree with those in the table If a setting does not agree change it to the one in the manual 5 If the Node ID numbers on your units were changed because you are controlling more than one system with your computer set them to the values they were changed to The factory setting default values are 65 for LoadTrac ll 66 for the FlowTrac ll unit controlling cell pressure and 67 for the FlowTrac ll unit controlling sample pressure ll 4 Q We noticed that a lot of the clay in our specimen has been washed into the sample flow pump We think that the flow pump might now contain soil deposits after some time of use What is your opinion Do you have a similar experience Does the washing of the fine materials into the flow pump affect the readings of the pressure transducer Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp A Fine materials do not affect the readings of the pressure transducer but they will cause the valves to become clogged and not function as designed Foreign material sucked i
7. 30000 counts as seen in the left hand text field second from the top on the System Monitor window 3 Record both the Displacement reading in mm or in and the Pulse Count for the Load Motor Note that the Pulse Count is the motor step count Now move the platen up until the displacement reads 40000 to 50000 counts Again record both the Displacement reading in mm or in and the Pulse Count Calculate the Load Step Multiplier as follows T Load Step Multiplier A Vertical travel A Pulse count 7 Open the Hardware Setup window select the Hardware item on the Options menu and replace the Load Step Multiplier value with the one you have calculated Then click the Apply button VII 8 Q would like to run a stress path extension test AE keeping the cell pressure constant and decreasing the vertical pressure to simulate a field situation of a foundation unloading or excavation How do do this Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp A To run an extension test you will need the special hardware accessories described in Q A Il 5 in the Hardware section The following steps will lead you through running the AE test 1 Before filling the test cell with water be sure the piston with the threaded nipple has been screwed securely into the sample top cap designed for an extension test After filling the cell with water be sure
8. Horizontal Vertical properes BEES BIENES Step Stress Stress tested Control Rate Strai Time Table kPa kPa min E min 1 0000 ricas a L Iairicui Strain 2 e O02 Strain 1 0 u T T 5 r 2 0 110 Relative D D rained Stress 1 5 10 5 Time T 3 1000 Relative Drained Strain 2 ee 20 0 Strain T 4 0 Absolute Undrained Strain 0 j Time T 5 0 Absolute Undrained Strain l 0 0 Time T EU j Absolute Undrained Strain 0 0 Time T 7 0 0 Absolute lIndrainmed Strain 0 Time 8 0 Absolute Undramed Strain 0 0 Time T g 0 Absolute Undrained Strain D 0 Time 1 0 0 Absolute Undrained Strain l 0 Time T l Loading and Unloading Stress Strain Curve using Stress Criteria Vil SHEAR PHASE Vil 1 Q What is the expected excess pore pressure during an undrained shear of granular soil A The graph below shows the typical qualitative behavior for the excess pore water pressure during an undrained shear phase of a triaxial test Note that the pressure as a function of strain for a loose sample is quite different from that of a dense sample Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp A Loose Sample Dense Sample m d p 3 a N p a p s n a Q o x i
9. Strain VII 2 Q In what unit is the shear rate The software program shows the Rate as min with no unit in the numerator A The unit for rate depends on the Shear Step Control parameter you have chosen If you have ou chosen Strain the rate is min see first Step Maximum Maintain Control Strain Time example at right If you have chosen Stress the i 2 min rate is kPa min for metric units or psi min oe i English units See second example at right If you wish you can choose a different unit for stress and or for time The choice of units is Step bum BERTA made on the window opened by selecting the ae sis Mc Units item on the Options menu Then the rate Undrained t B o under Strain control will be chosen time unit and the rate under Stress control will be in chosen stress unit chosen time unit See the Pis Step p Maximum Maintain third example at right where the rate would be Type m ims chosen stress unit sec Umdrsimed Stress LDBDOBGEGEE 2 Jo VII 3 Q Is there a strain rate that you recommend for the shear phase A The strain rate should be calculated according to ASTM standard D 4767 Section 8 4 2 as follows 8 4 2 Axial Loading Apply axial loading to the specimen using a rate of axial strain that will produce approximate equalization of pore pressures throughout the specimen at failure Assuming failure will occur after 4 a su
10. and thereafter at every 1 Take sufficient readings to define the stress strain curve hence more frequent readings may be required in the early stages of the test and as failure is approached Continue the loading to 15 strain except loading may be stopped when the principal stress difference deviator stress has dropped 20 or when 5 additional axial strain occurs after a peak in principal stress difference deviator stress These irregularities should not happen at the beginning of a test VII 7 Q While the triaxial test is running noticed that my strain rate is slightly different than the one that I specified in the Shear Table Why is that How can I set it up correctly A If the first two columns headed Time and Vertical Strain on the second page of the shear report table opened by selecting Shear from the Table submenu on the Report menu are used to calculate the rate during the shear phase the result should agree with the specified value to within 1 96 Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp TRIAXIAL TEST Project abck Location Home Boring Mo Tested By LE Test Date 10 72 708 sample Type soi Description Example Test data Remarks FUSer must put correct calibration factor in calibrate se specimen Height 150 44 nm Piston Area 103 23 mmz specimen Areal 4173 70 mt 2 Piston Friction 0 00 MW Specimen volu
11. and the undrained shear phase To help achieve these purposes it is definitely beneficial for the filter paper strips to be in contact with the porous stones A good reference on the subject is given below Titre du document Document title Influence af filter paper and leakage ontriaxial testing Auteur s Authoris LEROLIEIL Serge TAWENAS Francais L amp ROCHELLE Pierre TREMBLAY Michel Resume Abstract A significant problem especially in long term tests iz leakage through the fittings and membrane To avoidthe first of these tyro sources of error a cell with fittings enclosed ina back pressure chamber has been developed To reduce leakage through the membrane various cell fluids have been considered and tested in normal triaxial test conditions but with a dummy in place ofthe specimen The results shovwthat silicone ail minimizes the leakage Filler papers are Weed in triaxial testing to accelerate the consolidation process and the equalization af effective stresses within the specimen during shearing The drainage capacity af five different filter papers was measured and their effect onthe consolidation and shear processes vas evaluated by comparative tests The results zhowethat inthe overconsolidated range the filter papers are efficient however due tothe high coefficient af consolidation of natural clays in this range they are not really useful Inthe normally consolidated range the efficiency of the filter drains duri
12. in2 instead of the actual area of 587 mm2 0 197 in2 see sample graph above We typically use 148 mm2 0 23 in2 as the effective area Go to Options Piston Settings to make these changes Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp Effective Triaxial Piston Area Piston uplift forcs Ibs 0 50 100 Cell Pressure psi It may be that the effective area value you have in the Piston Setting window is not correct for your triaxial cell Go through the procedure of getting load cell readings while you increase the pressure in the cell Then plot the result and determine the slope of the line Excel works well for this Use the value of the slope for the effective area Ill 2 Q During the test a controller error message appears on the screen telling me that a limit switch is on What should I do A The first thing to do is to look at the front panels of the LoadTrac ll and FlowTrac ll units to see which unit has a red limit switch flashing If the flashing limit switch light is on the LoadTrac ll unit lock the piston and then open the System Monitor window Record the Load value in engineering units If the upper limit switch has been triggered lower the platen using the LoadTrac ll keypad and then lower the cross bar one notch If the lower limit switch has been triggered raise the cross bar one notch and
13. min 40 eo 20 40 2007 05 30 Shortcut to SQRT of TIME min SQRT of TIME min TRIAXIAL 5 Shortcut to Shortcut to Recycle Bin ICON Softw triaxial exe eo rii jeu Shortcut to Shortcut to shear exe X triaxial repo A Silty clay should not take this much time to consolidate According to our experience it should take only about 4 hours The graphs you have attached imply that there is a very small leak between the sample and the cell Normally the cell volume should not change very much once the target pressure is reached water is incompressible Your attachment shows 115 cc of cell volume change and still increasing The sample volume change is very high as well A quick calculation based on initial degree of consolidation void ratio and initial volume of sample shows that the sample volume change should not be 115 cc The typical height for a 70 mm 2 8 in diameter sample is 140 mm 5 6 in If this is the height of your sample its volume is 650 cc The volume change shown on your attached graph corresponds to almost 189e which is very high for this kind of soil and the effective stress applied We recommend stopping the test putting an additional membrane on the sample and starting the test again ll 7 Q We were expecting the T100 graph during the consolidation phase to level off Instead it turns back up What do you think is happening Geocomp Corporation 125 Nagog Park Acton MA 01720
14. new settings will not be saved V 10 Q We collected too many data points Is there a way to delete some A Yes Select Edit on the Report menu On the window that opens click Next until the phase containing the data you wish to edit is displayed Right click on the number for the row you wish to delete On the option window that opens select and click Delete See screen capture below 85 TRIAXIAL Data Shear Phase Step 1 Cell Sample Time Da Displacement Pressure Pressure msec cnts cnts cnts nts 1 i 2514 J322 53746 2 75070526 J 245 2514 3323 53746 3 75075538 155 244 2514 3324 537 46 TM gj 245 2514 33245 53746 Previous 2513 3329 53746 2513 3332 53746 2513 3334 53746 8 75125664 173 M 2513 3336 53746 9 75185810 191 25 2513 3352 53746 10 75245954 205 2513 3366 53746 Nl WAL VI SATURATION PHASE VI 1 Q I am running a triaxial test on a compacted sand material My saturation ratio Skempton pore pressure coefficient B does not seem to ever reach the minimum value Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp of 0 95 that I specified on the Saturation page Am doing something wrong Is there a technique to improve the initial saturation of the sample before starting the test A First check to be sure that your cell and sample pressure sensor calibration factors are correct If there is any reaso
15. rid of all the air bubbles l 2 Q Before starting the test noticed some air bubbles in the drainage backpressure tubes Is there any way to saturate the tubing once the sample is in the cell and the cell is full of water in order to save time A Yes The most thorough procedure involves two steps To get rid of the major bubble content connect a tube from a faucet to the bottom drainage valve second from the left on the base Run a tube from the top drainage valve far right to the sink Open both the bottom and top drainage valves Slowly turn on the water and let it flow through the sample system Watch the water as it comes out of the top drainage valve into the tubing to the sink When no more bubbles are coming out turn off the water close the valves and disconnect the tubing The second step is designed to get rid of any residual small sized bubbles and will help to speed up the saturation phase Connect a vacuum pump that has a water trap in the line to either the bottom or top drainage valve Connect a tube from a source of de aerated water to the other drainage valve With both drainage valves closed turn on the vacuum pump Open the valve to the vacuum pump and wait until the reduced pressure in the system equalizes a few minutes Close the valve to the vacuum pump and open the valve to the water source Wait until no more water is flowing into the system Close the valve to the water source and again open the valve to th
16. same as the Offset value on the Calibration Summary window If the calibration factor and the offset are correct reduce the vertical stress and horizontal stress values that have been entered on the Initialization page IV 6 Q Sometimes during the initialization phase we need to open the drainage valve the far right valve to get rid of the remaining air bubbles How will this affect the volumetric calculations A Opening the drainage valve during any phase of a test will definitely adversely affect the volumetric calculations If you see air bubbles in the line during the initialization phase we recommend that you abort the test and remove the triaxial test cell from the platen Then remove air bubbles by flushing the sample and bleeding the lines before putting the triaxial test cell back on the platen and starting the test again See the latter part of Section 6 1 Preparing a Specimen for details V REPORT V 1 Q When I use report software the scale does not change to what want For example if want to change the vertical displacement scale to negative 0 02 it will not change but if I change it to negative 0 2 it will change In this particular case the default minimum value is negative 0 05 A similar thing happens to normal and shear stress scales A The software tries to keep both the vertical and horizontal scale in a ratio of 1 1 so that the Mohr circles are actually circles not ovals Thus there are values in
17. the T100 value it is continually updated and will not be very accurate at the beginning of the step A way to determine when the value is a good one for the step is to view the graph that is on the window opened by choosing Test T00 from the View menu As the line being plotted becomes fairly straight after forming the knee the T100 value will not change very much This graph has to be viewed during the Consolidation B phase it will not be saved when the program goes to the Shear phase Example Dense sand with a T50 equal to 20 min From the table the recommended rate of strain 20 01 min because the dense sand column shows this value for a T50 of 20 min From the equation amp 22 10 x 20 20 01 9g min because the table shows e 2 2 for dense sand Note The best practice when running triaxial tests is to always make three tests on each soil type i e prepare three specimens from the same soil and run a test on each specimen When this is done the effective stresses for the final step in the consolidation phase needs to be different for the three tests Furthermore it Is very important to use the same rate during the shear phase for each test The Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp rate should be the value determined from the tso for the step that has the largest effective stress In order to do this it is necessary to ru
18. the scaling that are not acceptable to the software You may have to keep on trying different values to get the combination that is best for you V 2 Q After running a successful test we ran into troubles with the report We were not able to generate a report because all links on the report pull down menu are inactive Are we missing something or is the software not entirely installed A To make the links active parameters and data for a test must be loaded into the TRIAXIAL program so that they can be displayed on the various TRIAXIAL windows Go through the following steps to load a data file 1 First pull down the File menu 2 Next click on Load This will display a window that shows data files for tests that have been completed and for any test that is currently running Highlight the file name for the test you wish to load and then click Open 3 Finally pull down the Report menu You should now see that the options for Graph and Table as well as the Settings and Edit options are all activated Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp Using these options you can view the results of the test change various settings for the report and edit the test data points Remember that each time you change or edit any item you will need to save the file and load it again V 3 Q I have a question about graphing the results of a CU test Triax
19. the vacuum pump Open the valve to the vacuum pump and wait until the reduced pressure in the system equalizes a few minutes Close the valve to the vacuum pump and open the valve to the water source Wait until no more water is flowing into the system Close the valve to the water source and again open the valve to the vacuum pump Continue the opening and closing of the valves for several cycles of alternate vacuum and water transfer Finally close both drainage valves then turn off the vacuum pump and disconnect the vacuum and water source tubing Finally it is necessary to be sure there are no bubbles in the lines from the two FlowTrac I units to the test cell The following steps will lead you through the procedure for getting rid of any bubbles Use these steps for both the cell pressure unit and sample pressure unit 1 If the main menu shown below is not showing on the FlowTrac ll unit press the Esc key to display it FlowTrac II 1 Monitor 2 Position 3 Control 2 Press the 2 key to display the Position menu shown below Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING O 2013 Geocomp Corp 1 Empty 4 Jog 2 Fill 5 Control Valves 3 Press 1 on the keypad to select Open and then press Ent When you see water beginning to come out of the line press any key to stop the pump Visually inspect the line and continue pushing water out until you get
20. then raise the platen slightly using the LoadTrac ll keypad Now reapply the load you recorded using the LoadTrac Il LCD menus and keypad From the main menu select Control then Apply and Maintain Load then Final Load Using the keypad enter the load value you recorded and then press Ent Unlock the piston Click Retry on the error window If the flashing limit switch light is on a FlowTrac ll unit close the valve on the triaxial test cell to which the line from that FlowTrac ll unit is connected and then open the System Monitor window Record the appropriate pressure value in engineering units Depending on which limit switch was triggered refill the pump it was empty or empty it if it was full so that the pump is about 50 full Reconnect the line to the test cell valve Before opening the valve use the FlowTrac Il LCD menus and keypad reapply the pressure you recorded From the main menu select Control then Apply and Maintain Pressure then Final Pressure Using the keypad enter the pressure value you recorded and then press Ent Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING O 2013 Geocomp Corp Open the valve on the test cell and then unlock the piston Click Retry on the error window IV NETWORK COMMUNICATION IV 1 Q There is no communication between the LoadTrac Il FlowTrac Il and the PC What is going on A Check the Node IDs on the LoadTrac ll and Fl
21. 2 3 states Specimens shall be considered to be saturated if the value of B is equal to or greater than 0 95 or if B remains unchanged with addition of back pressure increments VI 3 Q We are having problems saturating a sample for a C U Triaxial test Our initial calculations from moisture content and density show the sample we are using to be at least 90 saturated The software equipment while monitoring the test gives a B factor that starts out at 0 15 and after running all night we have 0 65 Is this possible and why In addition if we stop the same test and restart the saturation reading during the tests always start again at 0 15 How is this possible A This behavior is possible if the lines are not fully bled prior to starting a test Air bubbles trapped in the lines the specimen and the pedestal and cap can drastically slow down the saturation process Refer Section 6 1 for how to get rid of all air bubbles VI 4 Q At the beginning of the saturation phase I noticed that the B value minimum saturation ratio went as low as 5 and then got back up to positive values after a while What should I do to prevent this from happening A Double the values of the T1 T2 and T3 on the Saturation page This will give more time for the water to move through the sample so that the B value determined during the T1 time is more representative of a steady state condition VI 5 Q I am getting negative values for B Skempton Pore P
22. TIME rain TIME rain VI 7 Q I am testing soft clay and I have already sheared a few samples during the saturation phase am using a pressure increment of 50 kPa and a pressure rate of 50 kPa min Why is my sample shearing prematurely A Both your pressure increment and your rate are too high for this type of soil For very soft soil samples you risk shearing the sample during the saturation phase if you use pressure and rate values that work well for stiff soils Try reducing the pressure increment to 10 kPa and the rate to 20 kPa If the sample still shears reduce the values even farther VI 8 Q We have several CU tests that report having a B value greater than 1 0 In some cases it is as high as 1 7 Any idea what may cause this to happen Your input would be greatly appreciated A Two possible causes for the B value being higher than 1 0 are an erroneous calibration factor for either the cell or the sample pressure transducer and a leak We suggest checking your calibration factors and re calibrating the pressure transducers if there is any reason to believe the factors might be wrong If there is a leak it should show up during the initialization phase as a flow of water from the cell FlowTrac Ill pump to the sample FlowTrac Ill pump You can look for this by displaying the system monitor on the LCD for each FlowTrac ll unit select Monitor from the main menu then choose Monitor The percent full value for each pump should not
23. TRIAXIAL TESTING 2013 Geocomp Corp Frequently Asked Questions Hardware Il BUBBLES IN LINES l 1 Q How do I bleed the lines and get rid of air bubbles in the cell A Getting rid of air bubbles is done at three places during the procedure of preparing a sample and Triaxial cell for a test First of all a few small air bubbles in the cell will not affect a test It is sufficient to tip the cell away from the valve on the cell top while filling it through a tube connected from a faucet to the cell valve on the base until water comes out of the top valve Getting rid of bubbles in the sample system is very important This is a two step process The first step gets rid of the major bubble content Connect the tube from the faucet to the bottom drainage valve second from the left on the base Run a tube from the top drainage valve far right to the sink Open both the bottom and top drainage valves Slowly turn on the water and let it flow through the sample system Watch the water as it comes out of the top drainage valve into the tubing to the sink When no more bubbles are coming out turn off the water close the valves and disconnect the tubing The second step is designed to get rid of any residual small sized bubbles Connect a vacuum pump that has a water trap in the line to either the bottom or top drainage valve Connect a tube from a source of de aerated water to the other drainage valve With both drainage valves closed turn on
24. TRIAXIAL TESTING 2013 Geocomp Corp VII 9 Q We have a triaxial test running and an error message that reads LoadTrac ID 65 Load reading of 65528 is out of range popped up during the Shear phase Why did this show up and how do we prevent it from popping up again A When you receive an error message stating Load reading of 65528 is out of range it means that the load cell sensor has maxed out The software program has a built in safety feature that shuts down the test when any of the sensors is giving either a minimum or maximum count reading which ranges from 0 655306 One possible reason is that the piston was left locked If that was the case you need to lower the platen unlock the piston and start the test again The other and more likely possibility is that your sample strength is greater than the capacity of the load cell It this is the case you will have to use a higher capacity load cell for the type of soil that you are testing For the very stiff soil situation the immediate action to take when this message occurs is to open the System Monitor window and record the Load value in engineering units Then lock the piston lower the platen and attach a higher capacity load cell to the cross bar If you know the calibration factors for the new load cell you can enter them on the Calibration Summary window type in the values and click Apply If you do not know the calibration factors you will have to calibrate the sensor
25. XIAL TESTING O 2013 Geocomp Corp wt TRIAXIAL E Set up_Files Customers Files inspecsol CIU 3651 9 BH 2 SHL5 30kPa dat File View Run Calibrate Control Report Options Help Project Specimen Water Content Read T able Test Parameters Initialization Consolidation T able Saturation Consolidation B Table Shear Table Pore Shear Shear Horizontal Vertical Stress Pressure Step Step Maximum Maintain Stress Stress Type Change Type Control Rate Strain Time psi psi psi min min 10000 Relative Absolute Absolute Absolute Absolute Absolute Absolute Absolute Absolute Absolute eo Undrained Strain Undrained Strain Undrained Strain Undrained Strain Undrained Strain Undrained Strain Undrained Strain Undrained Strain Undrained Strain Undrained Strain oO wo on mm S amp S CO IND oOooooooooo ooooooooo 41421242 242 42 1242 42 124212342194 coooooooooo i di adi adi al ala alata olelieliseieieie ie ooooooooorm ooooooooolkl 4 41 4 4142 242 2421 42 9421 94194 5 When reporting a UU test be sure to specify Total Stress and the showing of Mohr s Circle at Maximum Shear See the example below Report Settings General Stress Path Graphs Strain Graphs Total Stress v Minimum fo psi O Maximum 1 O0 p i gsis fv Minimum fo psi O Masimum 5 Y psi Iv Show Strength Envelope F Show Mohr s Circle at Maximum Shear User Specified St
26. act that the Membrane Correction Factor on the Test Parameters page is higher than the soil strength itself If you replace the Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING O 2013 Geocomp Corp Membrane Correction Factor value with zero your graph will be positive and will look more like that shown below l li Ml E a o uU Lo fe o I ad lt i c VERTICAL STRAIN 75 V 7 Q Is it possible to view the data and graphs while a test is in progress A You do not need to wait until the end of the test While the test is running 1 Goto the File menu 2 Select and click on Load 3 Goto the Report menu You should now be able to see the partial data up to the point when you did the Load 4 Repeat the above steps as the test progresses V 8 Q How can I print my tables and graphs at the end of the test A To print the table or graph for a completed test follow IE eq these steps Previous Page Ctrl Up Next Page Ctri Down 1 Bring down the Report menu a 2 Select Table or Graph FR Width CreW 3 Click on View at the upper left corner of the window that Fit Length Ctrl L opens see illustration below then select print Print Ctrl P Close Ctrl X V 9 Q Some triaxial test results are showing negative cohesion intercept Is this possible Can we adjust the cohesion intercept so it is equal
27. alization the FlowTrac ll s use the water that was drawn in only during the initialization Ill 10 Q Do need to provide piston friction and piston weight or is this information redundant for the test A It is good practice to include piston weight since this is accounted for in the deviator load computations Piston friction is not necessary to include Ill 11 Q The software manual says that the Proportion Gain can be as high as 5 for soft soils and as low as 0 5 for stiff soils Also the Integral Gain should probably be set to 0 1 for very stiff samples What other values might be used and how are we going to decide on the best values to use Please clarify A It is possible to use any Proportional Gain P Gain value from 0 5 to 5 and any Integral Gain I Gain from 0 1 to 1 The Derivative Gain value of 0 should not be changed The rate at which a load is applied at the beginning of a step depends on both the P Gain and the I Gain lower value slower rate higher value faster rate The time to reach a target value increases by a factor of about 3 from a P Gain of 0 5 to 5 The table below gives general guidelines for P Gain settings Recommended P Gain LOOSE VERY SOFT 50 o 25 5 0 MEDIUM SOFT MEDIUM 2 5 DENSE STIFF In addition the following information may help you to decide what value will be best for your sample The graphs shown below are for loading curves generated during a test They were
28. alues or specific values Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp Stress Paths from K 0 67 Condition Unloading Loading 3 Compression dewatering consolidation Ko loading foundation loading pure shear active wall pore pressure buildup excavation unloading pure shear jack reaction 1 2 3 4 5 6 7 8 9 Extension 0 20 Vil 11 Q In the TRIAXIAL software manual there is no mention of a UU Triaxial test How can we perform an Unconsolidated Undrained UU or Quick Q Triaxial test on this equipment A Below are the step by step instructions for running a UU triaxial test with the LoadTrac Il FlowTrac ll system and the TRIAXIAL software 1 Close all valves to the sample top and bottom drainage lines on the triaxial test cell 2 Fill out the Initialization page with the values shown below Horizontal Stress 120 kPa Vertical Stress 120 kPa Sample Pressure 0 kPa Stress Rate 140 kPa min Duration B0 min Read T able Time e 3 Make all entries on the consolidation A Saturation and Consolidation B pages zero so the TRIAXIAL program will skip these phases and go directly from Initialization to Shear 4 Onthe Shear page use the set up shown in the example below Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIA
29. amp R e A m e Volume Displacement Displacement Displacement Displacement Displacement Displacement Displacement Displacement Displacement ooocoooocoo 5 oOooooooooowu eejie ie ie ie e ieie w oOooooooooogm 4142142142 42142 142 12421 241 4 ooo ooo ool oe ooo ooo ol ol O 4i d i ad lala lata tata t a 2 3 4 5 B i 8 3 0 v Ko Consolidation Ko Gain 35000 kPa min Ko Pressure Limit 15 kPa The K used in a Ky consolidation is the coefficient of earth pressure and is defined by the equation Where the numerator and denominator are the horizontal earth pressure and vertical earth pressure respectively Ko is the coefficient of earth pressure at rest i e when there is no lateral movement For this situation K 1 sin p Jaky s Solution 1944 where the angle is the angle of shear resistance the effective internal friction angle Kmax is the maximum value of the coefficient of earth pressure Kmax is known also as the coefficient of passive earth pressure K about 3 0 Kmin IS the minimum value of the coefficient of earth pressure Kmin is known also as the coefficient of active earth pressure K about 0 3 The K Gain that needs to be entered on the Consolidation B page second text field from the bottom is approximately equal to the bulk modulus of the soil Unfortunately the letter K is used also to specify bulk modulus The equation shown below defines the bulk modulus
30. ark Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp 85 TRIAXIAL C Carolyn Software QA TRIAXIALW8 20120822 triaxial Al dat File View Run Calibrate Control Report Options Help Saturation Consolidation B Table Shear Table Read Table Test Parameters Initialization Consolidation A Table Start Phase Initialization Consolidation A C Saturation Cansalidation B Shear Area at end of Consolidation Method A Area Correction None Method B Uniform Parabolic Fitter Strip Correction Factor 273709531578 kPa Membrane Correction Factor 0 735532937007 N mm Time ta 50 Consolidation 0 min Test Type Consolidated Undrained Test Standard N A Show Strength at 7 Maximum Obliquity Maximum Shear mas Specified Strain Strain 10 E 2 Enter your desired strain value 5 10 or any other value 3 Bring down the File menu and select Save as Save your file with a modified name 4 Reload the saved file The software program will now pick the strength at the strain that you specified 5 Repeat for the remaining tests of the series V 5 Q How do you delete a bad set of sensor readings at the completion of a test A First confirm that the particular reading set is really bad due to an electrical power surge or some other unusual circumstance If you are certain the set should be deleted follow these step
31. be changing significantly Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp VI 9 Q Is it possible that the B value will drop during the cycling step of the back pressure saturation A This is possible if the time interval to allow for the pore pressure equalization during the back pressure saturation specified by the T2 value on the Saturation page was not long enough resulting in pressure changes only at the sample ends Then when the cycling step is reached the B value will drop reflecting the continuing equalization throughout the sample A drop in B value will not have any negative effect on the test VI 10 Q am getting negative B values at the beginning of the saturation phase How could that be possible A Yes it is possible to initially get some small negative values of B if the T1 and T2 values are relatively small and the soil sample is a stiff to very stiff material Eventually the B value will become positive and start to ramp up When a very stiff material is being tested we recommend that you use values of 15 min and 10 min for T1 and T2 respectively If the valve for sample pressure is closed on the triaxial cell it is also possible to get similar results Please see the Triaxial Cell manual for more information about correct valve settings Another cause can be air bubbles in the sample system Make absolutely sure that you hav
32. c strain See example graph below Ko Consolidation Ko test data Axial Strain Volumetric Strain When running a K test be sure that the following conditions are satisfied 1 The triaxial cell has to be filled with de aerated water 2 The stress rate has to be as slow as possible for the software program to make the appropriate closed loop control adjustments 3 The temperature of the lab should be maintained as constant as possible Il 4 Q I noticed that the cell volume starts to fluctuate as cell pressures greater than 900 kPa 125 psi are applied see attached graph Why does it do this Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING O 2013 Geocomp Corp 2n 4n an SORT af TIME min A The fluctuations you have observed can be the result of the cell pressure I Gain setting being too high for the pressure you are applying As each step in the consolidation phase applies a higher and higher effective stress the sample compresses and gets stiffer and stiffer The default I Gain setting of 0 1 works well for most soil conditions While trying to maintain the target pressure the FlowTrac ll will try to make adjustments too quickly which will result in sequential overshoots and undershoots of the target value Bring down the Options menu and select PID On the sub menu that opens select Cell Pressure to
33. dow opened by selecting Piston on the Options menu These other factors are the area of the piston the weight of the piston the friction on the piston and the uplift buoyancy force on the piston due to the cell pressure The weight of the piston adds to the load reading while the friction and buoyancy force subtract from it see diagram below The buoyancy force is the product of the cell pressure and the piston area Unfortunately it is very difficult to determine the actual frictional force on the piston However there is a way of getting around this a way that also eliminates the need for the piston weight The combination of weight friction and buoyancy force can be replaced by an effective buoyancy force that is equal to the product of the cell pressure and an effective area Putting this effective area in the Area text field on the Piston Setting window and then leaving the Weight and Friction text fields with zero is equivalent to using the actual area weight and friction values We determined the effective area of the piston for our standard triaxial system with the 3400 model triaxial cell We did this by increasing the cell pressure while the cell was in contact with the load cell button and the platen was fixed in position and recording the corresponding load cell reading A picture of the setup used and a sample graph of the result are shown below The effective area turned out to be between 130 mm2 0 2 in2 and 226 mm2 0 35
34. e removed all bubbles from the region between the sample and membrane and from the sample pressure lines This can be done at the beginning of the test using the procedure described in Section 6 1 VI 11 Q was just wondering if there was a way to set up the triaxial test to do an unloading reloading cycle A Yes you can Using the Shear Table you can setup the load unload and reload specifics The important note is how and where you would like to stop the unload portion of the shear before loading again you can use deviator stress or axial strain as your criteria which will depend on your particular application Stress Criteria It is good practice to reach a certain deviator stress during the loading then unload to about a minus of the deviator stress reached before loading again The rate must be stress control Strain Criteria again depends on your application and the soil type that you are testing you may want to stay within the elastic portion of the stress strain curve The rate must be strain control See the example on the following page Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp 500 200 100 DEVIATOR STRESS kPa O 2 10 This max strain value 18 B i VERTICAL STRAIN This unload stress value usually corres ponds tots ofthe stress reached depends onthe elastic just onthe first step i Shear
35. e vacuum pump Continue the opening and closing of the valves for several cycles of alternate vacuum and water transfer Finally close both drainage valves then turn off the vacuum pump and disconnect the vacuum and water source tubes You are now ready to put the test cell on the platen connect the cell and sample pressure tubing and start the test Il GENERAL Il 1 Q Can I fill up the triaxial chamber using the FlowTrac ll unit A Although is certainly possible to do so it is not practical to fill the triaxial cell chamber using the FlowTrac ll unit The total volume of water required to fill the standard model 3400 triaxial chamber is about 2500 ml and the total volume capacity of the pump cylinder in the FlowTrac ll unit is 250 ml The easiest and most practical way to fill the triaxial chamber is to do so directly from the water faucet or syphon water from a bucket into the cell Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp Note There is no particular requirement for the quality of the chamber water as long as the water is clean Water that is drinkable satisfies this requirement il 2 Q Do I need to use de aerated water to fill the FlowTrac Il units if so how dol obtain de aerated water A Yes it is important to use de aerated water in the FlowTrac ll pumps This will minimize the water air content thereby speeding up the back satura
36. eginning of the test have this window telling me Unlock the piston Press ok when ready For which phase do I need to lock the piston again A Once the piston is unlocked before a test starts it should stay unlocked throughout the entire test i e until the test is finished So you should not lock the piston until the test has ended and you are ready to remove the triaxial cell from the LoadTrac ll platen Ill 2 Q How does the TRIAXIAL program account for the membrane and filter corrections A The TRIAXIAL program uses the following equations to account for the membrane and filter corrections The correction for membrane stiffness is given by MSCOR e x l xCMEM CMEM is the membrane stiffness factor Bishop and Henkel 1957 describe an experimental procedure to measure CMEM and give typical values of 1 65 lb in for a standard 1 4 inch diameter membrane of 0 008 inch thickness and 2 0 Ib in for a 4 inch diameter membrane of 0 01 inch thickness If filter strips are present an additional correction for filter strips is made The correction that ignores any correction for membrane stiffness that is given by FXCOR FSC ee 0 lt lt 0 02 Bishop and Henkel 1957 suggests a value of 2 psi for FSC on 1 5 inch diameter samples with vertical filter strips covering half of the sample s circumference and 0 5 psi on 4 inch diameter samples Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fa
37. ess see next Q A on the sample m Allows the user to detect early leaks either through the latex membrane the fittings or the triaxial cell acrylic chamber not tightened O rings out of alignment etc m Applies a small effective stress on the sample so that the sample state of stresses is moved away from the failure line on a stress path diagram This will prevent any possible early set up failure of the sample especially for very soft soils or very loose sands Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp IV 3 Q What typical magnitudes of stress would you apply during initialization prior to beginning backpressure saturation A Typically you want to apply a small effective horizontal and vertical stress on the sample such as 20 to 27 kPa 3 to 4 psi The Sample pressure should be approximately 7 kPa 1 psi The Stress rate can be approximately 140 kPa min 20 psi min See example below Horizontal Stress 20 Vertical Stress 20 Sample Pressure Stress Rate 140 kPa min Duration 60 mir Head Table Time T IV 4 Q How long do I have to leave the initialization phase running A 60 minutes is a sufficient duration to detect any problem in particular leaks Note that if 60 minutes is specified on the Initialization page the phase will run for slightly longer than that if it is not stopped manually The dura
38. g back to the imbedded controller default values 4 Now go to your LoadTrac ll and FlowTrac Il hardware manuals In Section 2 1 4 of each manual Setup section you will find a table of default settings for your system Got through each LCD menu and be sure the settings on the menu agree with those in the table If a setting does not agree change it to the one in the manual 5 If the Node ID numbers on your units were changed because you are controlling more than one system with your computer set them to the values they were changed to The default values are 65 for LoadTrac ll 66 for the FlowTrac ll unit controlling cell pressure and 67 for the FlowTrac ll unit controlling sample pressure V 2 Q Can we turn off the PC while the test is running because this test is time consuming A No absolutely NOT but you can use other windows programs while the test is running and you can turn off just the monitor VI SAMPLE PREPARATION V 1 Q What is the purpose of the filter paper Are these strips supposed to be in contact with the top and bottom stones Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING O 2013 Geocomp Corp A Filter paper is used for two purposes 1 To speed up the consolidation process by providing radial outward drainage and 2 To help pore pressure equalization over the top and bottom areas of the sample during both the backpressure saturation phase
39. hould be back to normal IV 3 Q The Network LEDs are Red on the front panel of the LoadTrac Il unit and both the FlowTrac ll units There is no communication between the PC and any unit All of our ID numbers are correct What else should we check A Probably the network communication cable gray cable is plugged into the Ethernet jack on the back of your PC instead of into the special black adapter that is plugged into the network communication card that we provided If you find that this is the case unplug the cable and plug it into the adapter on the card see picture below The LEDs should now glow a solid green Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp V POWER OUTAGE V 1 Q After an electrical power problem in our building it seems that the system is not working properly We suspect that the set up values on the embedded controllers are not correct How do we revert to the original set up values or default values set at the factory A The default values may change either after an electrical power problem or due to inadvertent actions by the end user You will need to revert back to the internal default values of your system by following these steps 1 Turn off the LoadTrac ll unit and the two FlowTrac ll units 2 Wait about 10 sec 3 As you turn each back on immediately press the ESC key on the keypad to reset everythin
40. ial reports have the option of graphing either max shear or max obliquity Could you explain the difference and when you d report one instead of the other Up to now we have been reporting max obliquity for each test A You should use the maximum obliquity for CU tests and maximum shear for CD tests When reporting maximum obliquity you should specify Effective Stress on the Stress Path Graphs page of the Report Setting window The failure condition for this setting Is the maximum principal effective stress ratio 6 03 max When reporting maximum shear you should specify Total Stress on this window The failure condition for this setting is the maximum principal total stress ratio 0 o3 max V 4 Q We are using the TRIAXIAL Report software program to present consolidated undrained tests We normally assume failure to occur at either the maximum deviator stress 10 strain total stress maximum effective stress ratio or 5 strain effective stress have not been able to find a way to present Mohr s circles using the 5 or 10 strain limitations using TRIAXIAL Report Is there a way to do this A Yes You can present the Mohr s circles for any strain level The following steps will lead you through how to do this 1 Click the Test Parameters tab to display the Test Parameters page At the bottom of the page where it says Show Strength at click the circle beside Specified Strain Geocomp Corporation 125 Nagog P
41. ibrate window But you forget to click the Save button on each window before closing it Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp You now have a control program that has the correct calibration parameters on each Calibrate window and they will be different from those in the Calibration Summary However it is the incorrect Summary values that will be used to run the test If you know or suspect that a test was run using a file with incorrect calibration parameters on the summary window you can recover from the error Error Recovery Open a TRIAXIAL control window and load the erroneous test file into it You will need to replace the calibration parameters factors and offsets that are shown on the Calibration Summary with correct ones If you are certain that the parameters on the individual Calibrate windows are correct simply click Save on each of those windows If you will have to enter new values manually there are two ways to do this 1 delete the original values and type the new ones into the text fields or 2 copy and paste the new ones For the second option you will need to open a second copy of TRIAXIAL and load the test file that contains the correct calibration parameters Finally save the file and reload it The new values will be applied to the processed data Note The raw data and the results of data reduction shown o
42. itable rate of strain may be determined from the following equation 4 107 50 3 Where T50 time value obtained in 8 3 5 If however it is estimated that failure will occur at a strain value lower than 4 a suitable strain rate may be determined using Eq 3 by replacing 4 9o with the estimated Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp failure strain This rate of strain will provide for determination of accurate effective stress paths in the range necessary to define effective strength envelopes The table below will be helpful in determining a good strain rate Recommended strain Rates in min SAND Very soft CLAY Very Stiff Stiff Medium Soft plastic Strain at Failure e 1 2 4 8 96 15 You will need to know the type of soil you are working with and the T50 value the time for 50 primary consolidation that can be determined during the consolidation phase Then you can use the table to find the recommended strain rate Or you can use the table to get an estimated value for the strain at failure e and use the equation s 10T50 The easiest way to get the T50 value for a consolidation phase step is by dividing T100 by 6 The T100 value is shown on the Test Monitor window opened by choosing Test Monitor from the View menu But you need to wait until the test is well into the step before using
43. l Geocomp Corp software programs record the displacement transducer reading at the beginning of a test and then subtracts this initial reading from further readings before displaying the result on the Test Monitor window i e the transducer is zeroed at the beginning of the test Consequently the Test Monitor window shows the zeroed value not the actual reading The value shown in the report should match the Test Monitor value Ill 8 Q The phase relationship of my triaxial CU test does not look right am wondering what am doing wrong A The phase relationship calculations are affected by several factors such as the exact sample measurements loss of soil at the end of the test and assumed vs measured specific gravity We recommend exercising caution and using your best engineering judgment when reporting the data For example the degree of saturation should always be less than or equal to 100 For calculation details see Appendix E Ill 9 Q was wondering if once you initialize the FlowTrac and start a test if it is OK to turn off the water supply I ask because I have the system set up so that the water Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp supplies for both FlowTrac s are connected to a deairing chamber and would like to start deairing more water while one test is running A Yes you can turn off the water supply After initi
44. lowing requirement AV V Au 3 2 x 10 m kN 2 2 x 10 in Ib Where AV change in volume of the pore water measurement system due to a pore pressure change mm in V total volume of the specimen mm in and Au change in pore pressure kPa Ib in Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp NOTE 6 To meet the compliance requirement tubing between the specimen and the measuring device should be short and thick walled with small bores Thermoplastic copper and stainless steel tubing have been used successfully The tubing that connects a FlowTrac ll unit to the triaxial test cell is a thermoplastic material has small bore and is thick walled Its length is sufficiently short for the equipment to be in compliance with the ASTM standard ll 10 Q While running a triaxial test we keep getting an error message that the Sample FlowTrac ll is full What could be the problem A You have a leak at either one or both of the following locations 1 Most likely the leak is in the top drainage lines Make sure that the small O rings are in place and lubricated Also make sure that the drainage lines are pushed all the way into the top cap holes until they hit the top porous stone 2 The other possibility is that there is a leak in the membrane If this is the case use a new membrane or use two membranes recommended Fo
45. me 605 41 cc Piston weight 0 00 M Liquid Limit Plastic Limit wertical valumetric corrected Dewviatar Time Strain 1 Area Load min 58 mma 58 1 4173 7 5 0111 Z 0 0833283 0 0035475 n 4173 7 21 685 3 O 16 67 O 00088689 n 4173 7 356 043 4 0 25052 0 0026607 n 4173 7 45 312 5 0 5003 7 O 01419 4173 7 J r The two factors that determine how close the actual strain rate is to the value specified on the Shear Table are the displacement transducer calibration factors and the LoadTrac ll Step Multiplier First check to be sure that the displacement transducer calibration factors are correct If there is any reason they might have changed e g the transducer has not been calibrated recently or there was some event that might have affected the transducer functioning go through the calibration procedure described in Appendix A The Load Step Multiplier that depends on the characteristics of the load frame is carefully determined at the factory and is not likely to be incorrect However if the calibration factors are correct and the agreement is still outside 1 go through the following steps to obtain the Load Step Multiplier value that is now needed for your load frame 1 Open the System Monitor window select System from the View menu and then run the LoadTrac ll platen all the way down until it reaches the lower limit switch 2 Move the platen up until the displacement transducer reads about 20000 to
46. n the Position menu and press Ent Draining must be done into a container separate from the one you fill from After draining the cylinder fill it from a clean de aerated water source You need to repeat this operation several times or until you can see that the drained water is clear Leave the FlowTrac ll empty if you are not going to use it for an extended period of time Il 7 Q The FlowTrac ll is making a strange noise only when it empties Any idea why it is doing this A The V Limit PID setting for the embedded controller may need to be adjusted Follow these steps 1 Press ESC on the FlowTrac ll unit to display the LCD main menu if it is not already being displayed 2 Press 4 on the keypad to display the Setup menu Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp 3 Next press 4 to display the PID menu 4 Again press 4 to access the V Limit 5 Change the V Limit from the current value 16340 steps sec to 8192 steps sec Reboot the FlowTrac ll by turning it off waiting about 10 seconds and turning it back on This will cause the PID parameter change to take effect ll 8 Q When we unpacked our equipment and started to set it up I noticed that the plastic triaxial test cell now contains thousands of tiny hairline cracks mostly around the middle but some on the ends also Is this a problem A The presence of hairline cracks i
47. n the report pages will be changed The stress target values that were entered into the Initialization page the Consolidation Table pages and the Shear Table page will not be changed l 4 Q When I start a test the program gives me an error message stating that the calibration factor is too small cannot run the test checked the Calibration Summary table All values for the calibration factors are there however the LVDT calibration factor has a negative sign What s wrong A The software does not accept zeros or negative numbers for the calibration factors in the calibration summary The most convenient way to calibrate the LVDT is to add gage blocks between the LVDT shaft and the stop When this is done the output signal decreases for each increment and the resulting calibration factor is negative All that is needed is to remove the negative sign in the summary table and everything should work correctly liso Displacement 7 Factor 1 51 BB8z1448e D momicnt Offset 2405 chs Date Sun 15 NOV 2008 22 00 1 1 Cancel Download Apply Help Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING O 2013 Geocomp Corp l 5 Q used our calibrated gauge blocks to check our displacement sensor on the load frame It appears to give readings roughly one half the actual distances double checked that the calibration factor in cnt from the certificate you gave u
48. n the test with the largest final stresses first and enter the rate on the Shear page while the test is running then save the file before the shear phase begins CAUTION When entering or changing a value on a Properties Sheet page that has a table it is necessary to move the cursor to another cell of the table before clicking Save in the File menu If this is not done the entry will not be saved VII 4 Q How can we obtain the failure envelope after performing a series of tests on the same soil sample A If you have run a series of tests with different confining stresses and saved them under different filenames you can use the companion editing reporting software triaxial report exe to combine up to four tests and generate a failure envelope for them Follow the steps given below 1 Open the companion editing reporting program triaxial report exe bring down the file menu and click Load to load the first test file of the series 2 Bring down the Window list the first loaded program will be shown after the number 1 and click the number 2 The list will close and the TRIAXIAL REPORT control window will go blank 3 Bring down the file menu and load the second test file 4 Repeat this process for the additional up to a total of four test files TRIAXIAL REPORT 2 C Documents and Settings Geocomp Tria File Calibrate Report Options 1 C Documents and Settings Geocomp Triaxial CL Adat v 2 C Documents and Set
49. n they might have changed e g they have not been calibrated recently or there was some event that might have affected the transducer functioning go through the calibration procedure described in Appendix A Next you could try a technique widely used to improve the saturation process Flushing the specimen with carbon dioxide gas CO to replace as much air as possible prior to backpressure saturation is a good way to improve saturation because CO has higher water solubility than air The following steps will guide you through the technique 1 Dip the top drainage line far right on the base into a small container of clear water and open the valve 2 Connect a regulated source of compressed CO to the bottom drainage line second from the left on the base and open the valve on that line 3 Open the valve on the CO and slowly increase CO pressure until bubbles start escaping through the water into which you have put the top drainage line Continue flushing the sample with CO for about 15 minutes 4 Close the CO valve and the valve on the bottom drainage Replace the CO source with the de aerated water source 5 Open the valve on the bottom drainage line and apply a small vacuum to the top drainage line to force a slow upward flow of de aerated water into the specimen Continue until no more bubbles show in the top drainage line 6 Finally disconnect the device you are using to apply the vacuum and close the valves on both the t
50. ng consolidation iz considerably less than expected contrary to what has been observed by other researchers no effect of the titer drains on shear strength was found Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp Software Il CALIBRATION ZEROING l 1 Q When I view the system before starting a test there is always an offset of about 0 005 kN 1 Ib Why There is no contact between the vertical load cell and specimen so why is there a small offset in the load and how can I make it zero A Between tests the load cell output will usually drift a small amount At best the no load condition will be in the range of 0 025 of load cell full capacity which translates to about 30 001 kN 30 25 Ib for a 4 45 kN 1000 Ib load cell If you observe a no load condition on the System Monitor window that is greater than 0 025 of full capacity use the following steps to zero the load cell 1 Be sure the load cell is not in contact with anything 2 Bring down the Calibrate menu and select Summary to open the Calibration Summary window Position this window beside the System Monitor window 3 Note the Load reading in counts on the System Monitor window top left text field 4 Replace the Offset value that is shown on the Calibration Summary window when Load is selected for the Channel choice with the Load reading in counts that is on the System M
51. nto the pump can also damage the piston seal and cause premature pump failure However we do strongly recommend that you flush the FlowTrac Il pump after extensive use or after a long idle period To flush the pump simply fill and empty it several times making sure that you empty it into a different container than the one that you fill it from Il 5 Q What kind of hardware do need to run extension tests A You need the following items available from Geocomp Corp to be able to run an extension test 1 Coupler adapter for attaching the triaxial piston to the load cell see top photo at right 2 Triaxial piston with threaded 14 24 nipple at the end see bottom photo at right 3 Metal top cap standard diameters such as 1 4 2 8 etc with threaded hole to match item 1 see bottom photo at right 4 Two 4 20 bolts 1 long to fasten the triaxial cell to the platen not shown The bolts are fed up through the existing holes in the platen and screwed into the bottom of the cell Il 6 Q Is there any required maintenance for the FlowTrac ll units A Except for regular pressure sensor calibration and keeping the unit clean your FlowTrac ll units require only occasional maintenance The pumps should be flushed after extensive use and drained before an anticipated long idle time Flushing the FlowTrac ll pump is accomplished by first draining the cylinder using the FlowTrac ll keypad and LCD menus Select Empty o
52. ommended stress rate A Increasing the cell pressure by steps is preferable The step method will provide you with additional information about the sample consolidation properties However it is possible to increase the stress linearly The rate depends on the type and stiffness of soil being tested There is no one rate we can recommend However it is the case that the rate should be slower for a soft sample than for a stiff sample Il 3 Q understand that the TRIAXIAL program automatically runs a Ky consolidation at a click of a button How is K consolidation run A In order to run a Kg consolidation is necessary to put a check mark in the Ko box on the Consolidation B Table page by clicking on that box When this is done the page replaces the Effective Horizontal column with a Minimum K column and a Maximum K column see the example Consolidation B Table page below Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING O 2013 Geocomp Corp TRIAXIAL E SoftwareDEbug and Example_Dat_Files Triaxial Examples CkoUC1 dat File View Run Calibrate Control Report Options Help Project Specimen Water Content Read Table Test Parameters Initialization Consolidation A Table Saturation Consolidation B Table Shear Table Effective Minimum Maximum Vertical Stress Duration Maximum Minimum K Stress Rate Type Duration Duration kPa kPa min min min 1000
53. onitor window 5 Click the Apply button the Download button and then the Ok button to close the Calibration Summary window 6 You should now see in the System Monitor window that the vertical load cell reading in engineering units is within 0 025 of full capacity Note Steps 2 6 of this re zeroing process can be applied to any other sensor once it has been physically set at the zero condition l 2 Q What are the actual zero pressures for both the cell and the sample FlowTrac ll units at the beginning of a triaxial test A The pressure sensor for each FlowTrac ll unit is inside the unit Consequently any column of water in the tubing that goes from the unit to the triaxial cell will result in a pressure being registered by the pressure transducer at the beginning of a test Conventionally the zero pressure condition is the pressure for the top of the column being at the mid height of the soil sample in the triaxial cell just before the test is started assuming that there are no air bubbles trapped in the lines To adjust for different sample heights follow these steps for both the cell and sample FlowTrac ll units at the beginning of a test 1 Open the Output valve either using the FlowTrac ll keypad or the Valves Control window in TRIAXIAL 2 f the output line is connected to the cell disconnect it and be sure there are no air bubbles in it If it is not connected to the cell use the FlowTrac Ill pump to push water
54. op and bottom drainage lines For further information refer to m Rad N S and G W Clough 1984 New Procedure for Saturating Sand Specimens Journal of the Geotechnical Engineering Division ASCE Vol 110 No 9 pp 1205 1218 B Chaney R C Stevens Edward Sheth Niranjan 1979 Suggested Test Method for Determination of Degree of Saturation of Soil Samples by B Value Measurement VI 2 Q It seems that no matter what we do we can never achieve 0 95 B value during the saturation We used the carbon dioxide flushing method We increased the time intervals in the saturation table Is there anything else that we should try A You may never get a B value of 0 95 because of the soil type that you are testing See table below Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp Theoretical B Values for different soils at complete or nearly complete saturation Soil Type S 100 S09 Soft normally Consolidated clays 0 9998 0 986 Compacted silts and clays lightly over consolidated clays 0 9988 0 930 Overconsolidated stiff clays sands at most Very dense sands very stiff clays at high confining pressures 0 9130 0 10 BLACK D K ANDLEE K L 1973 Saturating Laboratory Samples by Back Pressure J ournal of the Soil Mechanics and Foundations Division ASCE Vol 99 No SM1 pp 75 93 Furthermore ASTM standard D 4767 Section 8
55. open the Cell Pressure PID Settings window Change the Integral Gain value to 0 1 and click Apply 2 Cell Pressure PID Settings al x Gains Proportional Gain 1 0 steps sec cnt Integral Gain L1 steps sec ont Derivative Gain 0 steps sec crt If there are still fluctuations reduce the Proportional Gain to 0 5 Note that the settings should be kept as high as possible so that adjustments will be made quickly but without fluctuations Il 5 Q I have run a series of CU triaxial tests on 37 mm diameter samples of silty clay see consistently that there are fluctuations in the deviator stress See Attached What is causing these fluctuations Are my tests bad A The graph looks good showing no fluctuations until the sample reaches failure At that point you should not expect a smooth curve because the sample is shearing A number of factors may affect the resulting shape of the post failure curve A few of them are listed below Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp Soil homogeneity Sample size Nature of the failure Soil consistency End effect Sticky piston Furthermore ASTM standard D 4767 section 8 4 2 1 stipulates the following 8 4 2 1 At a minimum record load and deformation to three significant digits and pore water pressure values to the nearestO 7 kPa 0 1 psi at increments of 0 1 to 1 strain and
56. ort Settings go to Strain Graphs From the Graph dropdown menu you can choose which Graph you want to change for the vertical axis Then from the Vertical Axis options below select what you would like to be displayed on the vertical axis Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266
57. ou will need to open a second copy of TRIAXIAL and load the test file that contains the new calibration parameters Save using the Save or Save As option in the TRIAXIAL file menu the altered test file When you load that file again the new parameters will have been applied to the processed data Note The raw data and the results of data reduction shown on the report pages will be changed Information that was entered using the various Property Pages will not be changed l 7 Q calibrated my transducer and filled out the Calibration table under the Options menu However can t get the program to save the new calibration numbers When I open Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp the file back up the old calibration numbers are still there How do save the new calibration data A Go to File gt Save As Save the file under a new name such as newtemplate dat Il CONSOLIDATION PHASE ll 1 Q What is the main drawback of applying a high effective consolidation stress in one step A If it is applied too fast you may prematurely shear your soil sample especially if it is a soft clay or loose sand and a small diameter sample such as 35 5 mm 1 40 in Il 2 Q If want to consolidate the sample under a high effective pressure is it better to increase the cell pressure linearly or by steps If linearly is best what is the rec
58. ow we can correct this so that we can run a test A It appears that your platen is all the way down almost close to the lower limit switch Please move the platen up until the displacement sensors read about between 20000 30000 counts then start the test Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp Ill LIMIT SWITCHES Ill 1 Q The platen moves down during the initialization phase until it triggers the lower limit then the test stops and an error message appears on the screen indicating that the lower limit switch is on Why is this happening A The behavior you have described happens when the TRIAXIAL program determines that there is already a stress being applied to the specimen that is greater than the Vertical Stress specified on the Initialization page This can happen if the sensor calibration factors are not correct First check to be sure these are correct and re calibrate the load cell and cell pressure transducers if there is any doubt see Appendix A for the calibration procedure If the load cell is not properly zeroed out before a test the same behavior will be evident The behavior can also happen if the factors the program uses to calculate the vertical stress are wrong The program determines the stress by combining the output of the load cell with three other factors that come from information on the Piston Settings win
59. owTrac ll units and in the TRIAXIAL program Hardware Setup window They have to be the same values The Node ID for each test unit is shown at the upper right on the screen of the unit The default values are shown in red in the examples below LoadTrac ll The TRIAXIAL Hardware Setup window is opened by bringing down the Options menu and selecting Hardware The Node IDs are shown in the Node ID text fields as seen in the example below Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp s TRIAXIAL WGeocompdc server d SHARED FILES Geocomp LAB SYSTEMS Systemsbackup CalendarYear2004 China_Uni E fi X File View Run Calibrate Control Report Options Help Consolidationz A T able Saturation Consolidation B Table Shear Table Project Specimen Water Content Read Ts act Parame itialisati PET ETDETUT mH Project Number GTX 0000 Boring Number B 205 Load Node ID Project Name ABC Test Number CL e 2 amp UU6 in step Load Step Multiplier Location Boxorough MA Sample Number B 205 Date of Test 00 00 0000 Depth 67 69 feet Cel Node DA 5 353e 004 cc step Tester rh fy Elevation Cell Step Multiplier Checker wam Sample Type Tube Cell Initial Volume 75 s a Auto Refill Description Moist olive yellowish clay Sample Node ID e PEDE Sample Step Multiplier 5 363e 004 cc step Sam
60. ple Initial Volume 50 Auto Refill Note that the Node IDs shown in the examples above are the default values set at the factory when the equipment was shipped If you reset the FlowTrac ll unit used to control the sample pressure by pressing the Esc Key right after turning it on that unit would revert to ID 66 Regardless of the reason that required you to reset the unit you must change the ID number back to 67 after resetting To do this select the Node ID option on the FlowTrac ll System Setup menu See the FlowTrac ll User Manual for additional details IV 2 Q We have several units connected to the same PC We were running only one of the units so we shut off the ones we were not using Then we got an error message stating that the unit we had left on was not responding It seems that we lost communication What is happening A A temporary loss of communication is normal when you either shut off or boot up any system unit connected to the same network Whenever a unit connected to the network is powered down or powered up the network goes into a re configuration mode during which no communication is allowed Depending on how many other units are on the network this process may take some time If the software checks connections while the process is going on you will get the not responding message If not no message will appear Should it appear simply wait a short period of time and then click the Retry button Everything s
61. r a single membrane put an additional O ring at each end at the sample side of the first O ring For two membranes put two O rings over the second membrane one on each side of the O ring holding the first membrane in place Any leak should show up during the initialization phase You should maintain the phase for at least 15 minutes preferably 60 minutes to make sure that the target stresses are held until the T100 condition is reached and that no water is flowing out of the cell FlowTrac ll to the sample FlowTrac ll ll 11 Q At the start of the test received an error message that the displacement is too low count reading is 6 7 to start the test A You will not get this error message if you raise the cross bar and then raise the platen until the displacement sensor reads between 7000 and 30000 counts before you start the test It is not a good practice to start a test with the displacement sensor close to its limit where it is nonlinear You should always start beyond the lower 10 range The full range of the sensor is 65536 counts so 10 of its range is 6554 counts Hence the suggestion of 7000 counts as the lowest starting value ll 12 Q Just after we hit start test a message appears saying that LoadTrac ID 65 pressure reading of 0 is out of range We have no calibration information for pressure in the software and we only have 2 A D channels on the machine One is for Force and the other is for displacement Do you know h
62. rength Envelope Intercept 7 909674669031 4 Cancel Apply Help VII 12 Q In the case where the deviator stress has not yet reached its maximum and the vertical strain is increasing past 15 on the summary results page we would like the Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp software to show that the strain at failure was 15 and also show the max deviator stress value that corresponds to when the axial strain was at 15 Is there a way for the software to automatically show these two values when this condition occurs A Yes the software will automatically show the strength and draw a Mohr circle at a specific strain level by using the option under test parameters df TRIAXIAL File View Run Calibrate Control Report Options Help Consolidation T able Saturation Consolidation B T able Shear T able Project Specimen Water Content Read Table Test Parameters Initialization Uniform Parabolic Filter Strip Correction Factor 0 psi Membrane Correction Factor 0 bein Start Phase nitialization f Consolidation f Saturation f Donsalidation B t Shear Test Type LIndrained Show Strength at f Maximum Shear t Specified Strain Strain x VII 13 Q In the shear report the deviator stress graph is displayed twice would like to keep only one How can I do it A From Rep
63. ressure Coefficient during back pressure saturation See attached graph What could be the problem Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp A The problem is either wrong calibration factors or a small leak in the supply solenoid valve inside the FlowTrac ll unit that is controlling the pore pressure You can check for a leak by inspecting the supply line for any water coming out during the saturation phase If you find evidence of a leak please contact Geocomp Corp for information about replacing the solenoid valve If there is no evidence of a leak calibrate the pressure transducer following the procedure given in Appendix A VI 6 Q Besides the B value is there another way to check the saturation of our sample A Looking at the B value is the only way to know accurately what the saturation status is However during the Saturation phase you can watch the sample volume vs time graph plotted in real time on the Test Graph window opened using the Test Graph option on the View menu The leveling off of AV is an indication that full saturation is being approached because it shows there is no more water going into the sample See sample graph below Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING O 2013 Geocomp Corp gt Saturation Phase E O x View 160 106
64. s 1 Bring down the Report menu 2 Select Edit 3 The window that opens contains a table of readings for the Initialization phase If the bad set is in another phase click the Next button until the phase you want is displayed 4 Right click on the number designating the row you wish to delete 5 he window that opens contains the choices of Delete and Insert Move the cursor to Delete and left click The row with the bad readings will be deleted and all other rows will be renumbered 6 Use Save As to save the file with a new name CAUTION Always keep the original test file intact in case the data set turns out not to be bad and you need to return to the original file Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING O 2013 Geocomp Corp V 6 Q The stress strain curves for my triaxial test looks wavy with negative values am testing a very soft soil Is there something wrong with what am doing A Probably your graph looks like the one shown below 7 7 iD a Uu U 5 Li a 7 ra e X T Q EE E E aE i im 2 ee e Se c e NO ca No Cn 15 VERTICAL STRAIN 26 If this is the case it is actually typical of very soft soils because the rolling effect of the membrane creates a rippling pattern see picture below The strength is gained by each rolling step The negative values can be explained by the f
65. s for sample dimensions calibration factors and PID control parameters Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp 2 Zero values for sample dimensions calibration factors except for offset value and PID control parameters 3 Wrong Node ID numbers 4 A malfunctioning sensor that it is giving an analog reading of either 0 the minimum value or 65535 the maximum value 5 Any unit LoadTrac ll or FlowTrac ll that is not on Ill 6 Q I am running a test Do I need to wait until the end of the test to see the results A You do not need to wait until the end of the test While the test is running 1 Goto the File menu 2 Select Load 3 Gotothe Report menu You will be able to see the partial test results up to the point when you did the Load 4 Repeat the above steps as the test progresses Ill 7 Q Why is the displacement value shown on the System Monitor screen different than the one shown in the Test Monitor screen A The System Monitor window shows the unadj usted reading of the displacement transducer displaying the result in counts and engineering units The value in engineering units is obtained by using the calibration parameters shown in the Calibration Summary window Summary option in the Calibrate menu The Test Monitor window on the other hand shows the distance the platen has moved from the beginning of the test Al
66. s is in both the load frame and the software factor 3 6498841x10 5 Does this factor seem to be off by a factor of two based on the other similar sensors you have calibrated A The calibration factor is correct The problem you describe can be caused by an incorrect setting for the polarity of the displacement sensor It hasto be Unipolar not Bipolar Use the keypad and LoadTrac ll LCD screen see illustration below to make the change as described in the following steps LoadTrac II Rev XX XX XXXX ID 65 1 Monitor 4 Setup 2 Position 3 Control Use the arrow keys to select option 4 Setup on the LCD screen From the Setup options select option 3 A D Setup From the A D Setup options select option 2 Channel 2 From the Channel 2 options select option 2 Polarity Of the two polarity options select Unipolar Finally turn off the LoadTrac ll and then back on for the changes to take effect ee ac dim l 6 Q Can I use a new calibration factor and apply it to the previous test I have already run and get the correct results A Yes you can Open the TRIAXIAL program and load the file for the test you had already run You will need to replace the calibration parameters factor and offset that are shown on the Calibration Summary with the new ones There are two ways to do this 1 delete the original values and type the new ones into the text fields or 2 copy and paste the new ones For the second option y
67. s very common When an acrylic cylinder is made it is normally cast and the thickened monomer polymerizes between two pieces of glass The shrinkage during polymerization is significant 21099 Asa result internal stresses are built into the acrylic material When the cylinder is cut to the needed length internal stress is relieved at the point of the cut but still remains in the rest of the sheet Also any slight imperfection on the surface will cause a localized concentration of those stresses and the cylinder could then form hairline cracks at that point In practical terms this is not normally a problem unless the cylinder is exposed to an aggressive environment UV from outdoor exposure over a long time normally years rather than days will cause surface cracks to appear as the stress is relieved These appear as crazing on the surface The most common occurrence in the laboratory is when the sheet is exposed to non polar solvents in the form of vapors ll 9 Q How does the Geocomp Corp triaxial system deal with the compliance requirement A The Geocomp Corp system uses the shortest and stiffest tubing possible with the smallest possible diameter to virtually eliminate any compliance in the system According to the ASTM standard D 4767 Section 5 8 Both measuring devices shall have a compliance of all the assembled parts of the pore water pressure measurement system relative to the total volume of the specimen satisfying the fol
68. sequently it is very important that these are correct To synchronize the LCD and PC screen readings you need to update the calibration parameters in the imbedded controller of the LoadTrac ll unit To do this follow the steps shown below 1 Bring down the Calibrate menu and select Summary TRIAXIAL C Program Files Geocom File View Run Belg Control Report Options Sutrnrmarsy Project Conso Load Displacement Cell Pressure Sample Pressure Pur Horizontal Vertical Stress Pressure Stress Stress Type Change kPa kPa kPa 2 Onthe Calibration Summary window select the sensor that you want to update from the list shown when the pull down button to the right of the top text field is clicked Li Calibration Summary Channel z Factor 0 5997617790596 M cnt Offset 32725 cris Date Mon O8 DEC 2008 14 39 24 Cancel Download Apply Help 3 Click the Download button This will automatically transfer copy and save the current calibration parameters Factor and Offset for the selected sensor into the embedded controller 4 Repeat the above procedure for the other sensors You should now see that the PC and LCD screen values match lll 5 Q Can the software detect wrong values that are manually entered by the end user A Yes the software program detects any erroneous values that have been entered It also detects certain hardware malfunctions Examples include 1 Negative value
69. set up the initialization saturation and consolidation phase in whatever way you feel is appropriate for your soil sample 9 Onthe Shear Table page use negative values for Vertical Stress and Rate You can run either a strain or stress controlled AE The sample Shear Table page shown below gives the values that should be used when strain control is used File View Run Calibrate Control Report Options Help Project Specimen Water Content Read Table TestParameters Initialization Consolidation 4 Table Saturation Consolidation B Table Shear Table Shear Step Type Shear Step Control Pore Pressure Change KPa Read Table Maintain Time min Maximum Rate Strain min Stress Type Vertical Stress KPa Horizontal Stress KPa e e e 10 Start the test according to the instructions in Section 6 2 Relative Absolute Absolute Absolute Absolute Absolute Absolute Absolute Absolute Absolute 40404 4 4 4 4 4 4 oc ojooooojojojojo oooooooooon ooooooooo0t oo ON Don Ff WN Undrained Undrained Undrained Undrained Undrained Undrained Undrained Undrained Undrained Undrained Y Strain Strain Y Strain Y Strain gt Strain 7 Strain Strain Strain gt Strain 7 Strain Y 2 e 002 9 9 9 9 9 9 9 9 9 oooooooo0o0wmu o 9 9 9 9 9 9 9 9 9 9 Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266
70. than 2 s To find out what the T100 value is for a step in a test open the Test T100 window by choosing the T100 option in the View menu at the beginning of the step As soon asthe ICONP program has gathered enough information it will show the graphical determination of the T100 value on the window It will also list the T100 value in the Test Monitor window To change a PID setting click PID on the Options menu to open the Load PID Settings window Replace the default value with the new value click the Apply button and then close the window Ill 12 Q Does the data that is obtained through the dump feature include corrections such as area membrane etc or is that raw data A The dumped data is raw data it does not include any correction IV INITIALIZATION PHASE IV 1 Q How can I change the rate at which the pumps fill during flow pump initialization The cell pressure pump appears to fill at a substantially slower rate than the sample pressure pump A The filling and emptying rates during the initialization process cannot be changed Filling the pump cylinders involves suction as a result the filling rate has been set so that no cavitation will occur IV 2 Q What is the purpose in general of the Initialization phase A Initialization is an important phase that m Allows the user to check the proper functioning of the entire system LoadTrac ll and two FlowTrac ll units while it is applying only a small effective str
71. the test was set up The two possibilities are described below The parameters are correct You have two LoadTrac ll FlowTrac ll systems A and B You plan to run a test on system A A file for a test run on system B is a good template for the test but the calibration parameters in it are those for the sensors on system B You open a TRIAXIAL control window and load that file into the window We will call that file Test B Next you open a second TRIAXIAL control window and load into it a file for a test that was run on system A We will call that file Test A Finally you copy the calibration parameters from the Calibration Summary in Test A and paste them into the Calibration Summary in Test A You now have a control program that contains the correct calibration parameters for running a test on system A but those shown on the Calibration Summary will be different from those on the individual sensor Calibrate windows The parameters are not correct You have two LoadTrac ll FlowTrac Il systems A and B You plan to run a test on system A Afile for a test run on system B is a good template for the test but the calibration parameters in it are those for the sensors on system B You open a TRIAXIAL control window and load that file into the window We will call that file Test B You decide to calibrate the sensors and use Test B to do it You go through the calibration procedure for each sensor and click the Calibrate button on each Cal
72. the piston is securely locked 2 Initialize the platen using the Initialize option on the LoadTrac ll Position menu so that the platen moves to its lowest position activates the lower limit switch and then moves up about 3 mm 12 in 3 Screw the coupler adapter onto the load cell and adjust the cross bar so that the test cell will fit under it on the platen 4 Bolt the Geocomp Corp supplied triaxial stress path cell to the platen This cell has two threaded holes at the bottom that align with the two non threaded holes in the platen Use two 4 20 bolts 112 long to secure the cell to the platen 5 Be sure the two clamping screws on the adapter have been loosened by about 1 4 and slowly raise the platen using the LoadTrac ll keypad and LCD menus until the piston slides about 34 into the coupler 6 Before tightening the clamping screws open the System Monitor window and the Calibration Summary window Be sure that the Load reading in counts on the system Monitor window is the same as the offset value on the Calibration Summary Window If they are different adjust the offset value so that it is the same as the Load reading 7 Make sure the piston is locked open the Load Control window specify a zero load in engineering units and click Go You can now tighten the clamp without generating a load on the piston Click Stop after the piston has been clamped in place Unlock the piston 8 You can use the Properties Sheet to
73. through the line until there are no bubbles See Q A 4 above for instructions to eliminate air bubbles Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp 3 Open the System Monitor window System option in the View menu and the Calibration Summary window Summary option in the Calibrate menu 4 Raise the end of the output line to the location that corresponds to the mid height of the soil sample Record the pressure value in counts that is shown on the System Monitor window the left hand text field for the pressure reading 5 On the Calibration Summary window select the appropriate Channel Cell Pressure or Sample Pressure Type the pressure value you recorded into the Offset text field Click the Apply button l 3 Q In many of our different test files the calibration values in the Summary Table and the values in each sensor s individual calibration table are not in sync Could you please explain which values the program uses and how to make sure they are correct A When running a test the TRIAXIAL software uses only the parameters that are shown in the Calibration Summary A mismatch between these values and those on the Calibrate window for a particular sensor can occur if the Calibrate window values have not been saved by clicking the Save button on that window To determine whether or not the Summary values are correct you need to know how
74. tingsxeocomp Triaxial CL B dat Consolidation T able Project Specimer After all the files have been loaded bring down the Report menu and select Settings On the Report Settings window that opens click the Stress Path Graphs tab If you have run undrained CU tests check marks should be in the boxes next to Effective Stress at the top of the window Strength Envelope and Maximum Obliquity If you have run drained CD tests check marks should be in the boxes next to Total Stress Strength Envelope and Maximum Shear Now you can select Graph on the Report menu to view the failure envelope and a table of test parameters VII 5 Q The shear rate seems to be varying during the shear phase want to make sure that the test is running according the standard Any comments A According to ASTM standard D 4767 the rate should be maintained with deviation of less than 1 of the target value See section 5 2 below Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp 5 2 Axial Loading Device The axial loading device shall be a screw jack driven by an electric motor through a geared transmission a hydraulic loading device or any other compression device with sufficient capacity and control to provide the rate of axial strain loading prescribed in 8 4 2 The rate of advance of the loading device shall not deviate by more than 1 from the selected
75. tion phase To prepare de aerated water boil water while applying a vacuum or use a device such as a Nold DeAerator which combines propeller cavitations with a vacuum to de aerate the water rapidly Il 3 Q Could the Node ID for either one of the FlowTrac ll units or the LoadTrac ll unit change by itself What possible reasons could you think to have prompted the change A The imbedded controller default Node IDs for LoadTrac Il and FlowTrac ll are 65 and 66 respectively When a second FlowTrac ll unit is supplied with a Triaxial system its ID is set at the factory as 67 The node IDs cannot change by themselves However if you reboot the second FlowTrac ll unit the one used for controlling the sample pressure and by mistake press the ESC key on the keypad at the beginning of the boot process the control program reverts back to the default value of 66 Similarly if for some reason you are using different Node IDs than those specified above because you are controlling several systems with one computer pressing the ESC key at the beginning of a reboot will change the ID for the unit being rebooted back to its imbedded controller default value If there is a possibility that someone pressed the ESC key at the start of the boot process for one or more units in your system go through the following steps to reset default values for the control programs 1 Turn off the LoadTrac ll unit and the two FlowTrac ll units 2 Wait about 10 sec
76. tion time starts from the moment that the stresses specified on the Initialization page are reached If you find no leaks and the test seems to be running as it should you do not need to wait for the full 60 minutes However you should wait until the T100 condition is reached To move to the next phase manually go to the Run menu and click on Next Step IV 5 Q My sample compressed during the initialization phase Why would this happen A Compression during the initialization phase can happen if 1 The calibration factor of the load cell is wrong smaller than the correct one resulting in a larger than intended load being applied 2 The offset value for the vertical load is wrong larger than the correct one resulting in the load starting at negative value 3 The sample is extremely soft If the load cell has not been calibrated recently you should check to be sure the calibration is correct or go through the calibration procedure for it see Appendix A Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp You can check the offset value by first lowering the platen so that there is no load on the load cell Then open the System Monitor window System option on the View menu and the Calibration Summary window Summary option on the Calibrate menu Check to be sure that the load count reading on the System Monitor window left box at the top is the
77. to zero Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING O 2013 Geocomp Corp A There are several factors that could cause a small negative cohesion intercept Three of them are the non consistency of the soil sample tested slight imbalances at the beginning of the shear phase and the sample not being fully in contact with the triaxial piston To correct the problem for purposes of the report using the TRIAXIAL REPORT software select Settings on the Report menu On the Report Settings window that opens click the Stress Path Graphs tab Put a checkmark in the box beside User Specified Strength Envelope near the bottom of the window Open the shear graphs window using the Shear option for Graphs on the Report menu so you can watch what happens as you change the Intercept and Slope values in the text fields at the bottom of the window You can put in values of intercept and slope to suit your needs After Stress Path Graphs Strain Graphs p Axis Effective Stress Total Stress V Minimum 0 Maximum 300 q Ais 4 Minimum 0 Maximum 100 v Show Mohr s Circle V Show Strength Envelope V User Specified Strength Envelope Intercept 0 Slope 22 ok Cenci Aw typing in a value click the Apply button and the new value will take effect CAUTION Before closing the program click Save All in the File menu Otherwise the
78. value The value shown on the Test Monitor window during the shear phase is based on the displacement transducer But the actual rate is produced by the micro stepper motor which is more accurate and precise than the displacement transducer Typically the displacement transducer is slightly non linear and has a resolution of 1 2 x10 mm count whereas the micro stepper motor will run at a constant rate and has a resolution of 5 3 x10 mm step If both the displacement produced by the micro stepper motor and the displacement determined by the sensor are plotted as a function of time and the linear correlation R2 is determined for each the results show that the correlation for the micro stepper motor plot is exactly equal to one This confirms that the test will run well within the standard of 1 of the target value Displacement Rates Analysis 3 H f From Micro Steps From Displ Sensor VII 6 Q I noticed irregularities in the excess pore water pressure curve and was wondering if you have any thoughts about it Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING O 2013 Geocomp Corp 40 we 9 20 am A Once the sample fails the additional data are meaningless and may not follow any trend This is why ASTM standard 8 4 2 1 specifies At a minimum record load deformation and pore water pressure values at increments of 0 1 to 1 strain
79. x 978 635 0266 TRIAXIAL TESTING O 2013 Geocomp Corp The corrected deviator stress on the sample equals the deviator stress minus the corrections and so is given by Ta 20 MSCOR FXCOR Ill 3 Q What are the area correction equations for uniform and parabolic A A no area correction l g uniform area correction Sample Area A Ay x l e l l l 4 X parabolic area correction 1 1 5xzg None Uniform Parabolic Area Correction Area Correction Area Correction C ee Original Shape of sample Shape of sample during test Ill 4 Q noticed that the engineering readings on the LCD screen are different than the ones on the PC screen Are they supposed to be the same Did it affect the results of a test I just ran A First be assured that any mismatch of the engineering readings values between the LCD and the PC screens will not affect the results of a test that you run using the TRIAXIAL program A mismatch can occur if the calibration parameters that are shown in the Calibration Summary opened using the Calibration menu have not been downloaded into the imbedded controllers of the LoadTrac ll unit and FlowTrac ll units However the software uses only the Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 TRIAXIAL TESTING 2013 Geocomp Corp Calibration Summary values when it runs a test Con

Triaxial - Geocomp

Contents

Download Pdf Manuals

Related Search

Related Contents