Frequently Asked Questions
Contents
1. m Allows the user to check the proper functioning of the entire system while it is only applying a small effective stress on the sample m Detects early leaks either through the rubber membrane the fittings or the in the cell acrylic chamber not tightened O rings out of alignment 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 clayey soils or very loose sands 6 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 stress on the sample such as 7 or 14 kPa 1 or 2 psi 7 Q How long do I have to leave the initialization phase A 60 minutes is a sufficient duration to detect any problem Please note that any phase duration starts from the moment that the desired stresses are reached If everything checks OK you do not need to wait for the full 60 minutes go to the Run menu and click on Next Step to manually override the automation process 8 Q I 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 SYNCHRONIZING LCD AND PC SCREENS First would like to assure you that the mismatch of the2. engineering readings values between the LCD and the PC screens will not affect the results of any test that you have run through the PC software program Assuming that your calibration factors are correct or that you have just finished a new calibration and need to update the calibration parameters on the embedded controller of a Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 PERM MS User s Manual 2013 Geocomp Corp LoadTrac ll or FlowTrac ll or ShearTrac ll you can synchronize the engineering readings between the LCD and the PC screen by following these steps 1 Go to the Calibrate Summary menu File view Run EASES Control Report Options Help 2 Select the sensor that you want to synchronize Calibration Summary Channel REN matte wet Factor 2 7435105e 002 Ib cnt Offset 132778 cnts Date Fri 24 SEP 2004 14 35 08 Cancel Download Apply Help 3 Click on the Download button This will automatically transfer copy and save the current calibration parameters Factor and Offset into the embedded controller 4 Repeat the above procedure for the other sensors 9 Q Can the software detect wrong values that are manually entered by the end user A Yes the software program detects any erroneous data entry examples include 1 Negative values for sample dimensions calibration factors and PID control parameters 2 Zero values for sample dimensions calib
3. permeability test on a compacted sand material My saturation ratio Skempton pore pressure coefficient B does not seem to ever reach the minimum value of 0 95 that I specified in the saturation table Am I doing something wrong Is there a technique to improve the initial saturation of the sample before starting the test Pressure Increment B psi Pressure Rate 50 psi min Minimum Cell Pressure Maximum Cell Pressure Minimum Saturation Ratio Maximum Number of Cycles Read T able A First check that your cell and sample pressure sensors calibration values are correct Next there is a technique widely used to improve the saturation process Flushing the specimen with carbon dioxide gas CO2 to replace as much air as possible prior to backpressure saturation is a great way to improve saturation because CO has higher water solubility than air Follow these steps Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 PERM MS User s Manual 2013 Geocomp Corp 1 Dip the top drainage line into a small container of clear water and open the valve 2 Connect regulated source of compressed CO to the drainage line at the bottom of the sample 3 Open valve on CO and slowly increase CO pressure until bubbles start escaping through the water Continue flushing sample with CO for about 15 minutes 4 Replace CO source with de aerated water source 5 Apply small vacuum to top dr
4. 266 PERM MS User s Manual 2013 Geocomp Corp A Because of the stiffness and compliance of the testing system which is just a small volume of the tubing you need to adjust the cell PID Proportional Integral Derivative parameter controls These are under Options PID Cell Pressure If you adjust the cell pressure proportional gain from to 1 00 to 0 25 you will see virtually no fluctuation in the pressure once it reaches the target value The PID control parameters are adjustable due to the nature of the different soil types and large variations in their stiffness from very soft peat and organic soils to highly over consolidated clays or even soft to medium rocks The max PID value is 0 10 very soft soils and the minimum is 5 00 very stiff soils PID CONTROL Control of the pressure or load is accomplished by using a closed loop controller At equally spaced time intervals called the control loop period the controller compares the target load or pressure to the measured load or pressure The loop error is the difference between the two The controller uses this error to compute and send a signal to the micro stepper motor in order to make adjustments to reduce the error by the next loop period The signal to the micro stepper controls the micro stepper s position The loop error computed by the controller at every loop period is nothing but the additional required load or pressure to eliminate the error by the next loop
5. 78 635 0012 Fax 978 635 0266 PERM MS User s Manual 2013 Geocomp Corp 14 Q We would like to run a perm test on a sample at 10 psi consolidation pressure then run it again at 103 kPa 15 psi then 138 kPa 20 psi and so on Is there a way to run it without losing the pressures initially created through the initialization phase and saturation phase A One way to do it is to run separate tests starting from the consolidation phase by skipping both the initialization and saturation phases To do so you need to either input zero s in both phases StartPhase Initialization or click Consolidation B under test parameters tab see tne attached and make sure at a the start of the test to Dor click NO to both initializing the platen and FlowTrac ee II s C Permeability Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266
6. PERM MS User s Manual 2013 Geocomp Corp Frequently Asked Questions Hardware 1 Q What are the actual zero pressure conditions for the cell and for the bottom and top FlowTrac ll units at the beginning of a permeability test A The pressure sensor for each FlowTrac ll unit is internally located therefore any column of water inside the tubing up to the cell will be registered at the beginning of the test This assumes that there are no air bubbles trapped inside the lines Conventionally the zero pressure is as follows FlowTrac ll Cell Pressure Soil sample mid height FlowTrac Il Bottom Pressure Soil sample bottom FlowTrac ll Top pressure Soil sample top It is extremely important that the zero pressures are adjusted at the beginning of each test Otherwise the gradient across the sample may not be correct To adjust for different samples heights following these steps for both the cell and top bottom sample FlowTrac ll units 1 At the beginning of the test open the Output valve either using the key pad or through the PC 2 Fill the output line with water making sure that there are no air bubbles trapped 3 Raise the line to the location that corresponds to the mid height of the soil sample and zero the pressure by placing the Offset value from the System Monitor into the Calibration Summary 2 Q Can I fill up the permeability chamber using the FlowTrac II unit A It is not practical to fill up the permeabili
7. ainage line to force slow upward flow of deaired water into specimen Continue until no more bubbles show in the top drainage line For further info please refer to Rad N S and G W Clough 1984 New Procedure for Saturating Sand Specimens J ournal of the Geotechnical Engineering Division ASCE Vol 110 No 9 pp 1205 1218 6 Q Could the Node ID for either one of the FlowTrac Il s change by itself What possible reasons could you think to have prompted the change A The Node ID cannot change by itself The Node IDs for the FlowTrac ll units used in permeability tests are 66 for the Cell Pressure unit 67 for the Bottom Pressure unit and 68 for the Top Pressure unit If someone rebooted the system and by mistake pressed the ESC key on the keypad of a unit the embedded controller for that unit reverted back to its default values The embedded controller default Node ID value for a FlowTrac ll unit is 66 If you suspect the ESC key was pressed during the boot sequence for any unit go to Section 2 1 4 Setup of the hardware manual for that unit There is a table of settings there Go through each LCD menu on the unit and compare the setting against that in the table If there is a difference change the setting to that in the table 7 Q We noticed that a lot of the clays in our specimen had been washed to the top flow pump We think that the flow pump might need some washing after some time of use What is your opinion Do y
8. e 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 this process may take some time If you re lucky the Windows software will miss it If you re not so lucky you get the normal LoadTrac not responding message All you have to do is hit the Retry button and you should be all set 10 Q After an electrical power problem it seems that the system is not working properly We suspect that the set up values on the embedded controller 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 each FlowTrac ll unit 2 Wait about 10 sec 3 Turn each back on and 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 Setup of each you will find a table of default settings for your system Go 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 numbe
9. g the sample from the bottom because the crossover to the top is closed The usual procedure is to saturate from both the top and bottom of the sample Does this cause the saturation and consolidation phase to take longer A The sample is being saturated and consolidated from both ends despite the cross over because both top and bottom FlowTrac ll s are active So it should be the same as the triaxial Software 1 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 Once a test is finished or even while it is running 1 Go to the File menu 2 Click on Load this will load the test data on the open window on the desktop 3 Go back to Report You should see now the Graph Settings and Edit menus all activated 4 You can change units and scales and edit the test data points 5 Remember that every time you change or edit something you will need to save the file and load it again 2 Q I noticed that the cell volume starts to fluctuate as soon as higher and higher cell pressure greater than 900 kPa 125 psi are being applied see attached graph Why does it do that 1 4 1 0 ic ox D S D o a 20 ac B0 40 SORT of TIME min Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0
10. lic conductivity is greater than about 1 3 10 m s but not more than about 1 3 10 m s then the size of the hydraulic tubing needs to be increased along with the porosity of the porous end pieces Other strategies such as using higher viscosity fluid or properly decreasing the cross sectional area of the test specimen or both may also be possible The key criterion is that the requirements covered in Section 5 have to be met You should consider using the quick constant head permeability method with this type of soil 13 Q How do I bleed the lines and get rid of air bubbles in the cell A You can saturate the lines and get rid of air bubbles by following the steps shown below m Using the keypad and the LCD on the front of the FlowTrac ll go to the main menu mThento 2 Position gt 5 Control Valves gt 1 Open output Valve and 4 Close the supply valve if it is not already closed 4 Jog 5 Control Valves 3 Open na 2 4 Close m Next go back to the main menu using the Esc key on the keypad Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 PERM MS User s Manual 2013 Geocomp Corp m Then to 2 Position gt 4 Jog gt use the arrow up to push water out of the flow pump into the output line until you see water dripping out Visually inspect the line and keep on pushing the water out until you get rid of all the air bubbles 14 Q Am I correct that we are only saturatin
11. nning a test Note that it is possible to have no calibration data in the calibration menu if you calibrate a sensor with one program for example PERM and later use a different program for example ICON Each program will always uses the calibration factors contained in its Summary Table 12 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 Increase the T s T1 T2 T3 T4 by doubling the values this would give the system time to settle down and adjust accordingly 13 Q How do you delete a bad point at the completion of a test A First find out if it is really a bad data point that is due to an electrical power surge or any other cause If such is the case follow these simple steps 1 Goto Report then Edit 2 Locate the bad point 3 Move the cursor to the first column and to the row number that you would like to delete 4 Right click on the mouse you should see a small window with the message Delete and Insert 5 Click on Delete the row with the bad point will be deleted 6 Save the file with a new name You must always keep the original test file intact The reported value should match the Test Monitor value unless other corrections are involved such as machine compressibility Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 9
12. ou have a similar experience Does the washing of the fine materials into the flow pump affect the readings of the pressure transducer A Yes you do have to flush the FlowTrac ll after extensive use or after a long idle period 8 Q Is there any required maintenance for the FlowTrac Il units A Except for regular routine pressure sensors calibration your FlowTrac ll units require only a little maintenance such as flushing and draining after extensive use or anticipation of prolonged idle time Flushing the FlowTrac ll units is accomplished by draining the FlowTrac ll pump cylinder manually using the Empty command on the front LCD Draining must be done into a separate container than the one you fill from 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 Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 PERM MS User s Manual 2013 Geocomp Corp 9 Q We have several units connected to the same PC We were running only one of the units so we shut off the remaining units Then we got an error message stating that the unit was not responding It seems that we lost communication with the unit What is happening A A temporary loss of communication is a normal thing when you either shut off or boot up another unit connected to the same network Any tim
13. period In other words the load rate is the error divided by the loop period Signal Error Loop Period Stiffness GP 1 Loop Period Stiffness Signal P GP Error The above equation is the basic idea behind any proportional controller where GP is the proportional gain The controller employed by this system is actually a PID controller where P is for proportional control is for integral control and D is the derivative controller 3 Q calibrated my transducer and filled out the Calibration table under the Options menu However I can t get the program to save the new calibration numbers When I open the file back up the old calibration numbers are still there How do I save the new calibration data A Go to File gt Save As Save the file under a new name such as newtemplate dat Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 PERM MS User s Manual 2013 Geocomp Corp 4 Q During the test a controller error message appears on the screen telling me that a limit switch is on what should do A Manually close the valve on the permeability cell connected to this FlowTrac ll Depending on the status of the FlowTrac ll unit refill if empty or empty if full Re apply the pressure from before the error message reopen the valve and then click the Retry button 5 Q What is the purpose in general of the Initialization phase A Initialization is an important phase that
14. ration factors except for offset value and PID control parameters 3 Wrong Node ID number 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 10 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 Go to the File menu 2 Select Load 3 Go tothe Report menu You should now be able to see the partial data up to the point when you did the Load Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 PERM MS User s Manual 2013 Geocomp Corp 4 Repeat the above steps as the test progresses 11 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 All of the Geocomp Corp control programs have similar menus for performing the calibration of any of the sensors related to the test However you must then copy the calibration that you obtained into the Summary Table If you have had to repeat the calibration procedure be sure to use the correct value The calibration factors in the Summary Table are the ones that the particular program uses when ru
15. rs 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 11 Q Why is the displacement value shown on the System Monitor screen different that the one shown in the Test Monitor screen A In all of our software programs the displacement reading is automatically zeroed at the start of the test therefore the offset value in the calibration summary for the LVDTs displacement transducers is irrelevant Also as a result the System Monitor non zeroed value will show a different value for the displacement from the Test Monitor zeroed value That is totally normal and expected Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 PERM MS User s Manual 2013 Geocomp Corp 12 Q We are using a sand sample and experiencing problems with water just flowing through the sample and triggering the limit switch A The flexible wall permeability test is suitable for soils with certain hydraulic conductivities according to ASTM 5048 1 3 These test methods may be utilized on all specimen types undisturbed reconstituted remolded compacted etc that have a hydraulic conductivity less than about 1 3 10 m s 1 3 10 cm s providing the head loss requirements of 5 2 3 are met For the constant volume methods the hydraulic conductivity typically has to be less than about 1 3 10 m s 1 3 1 If the hydrau
16. ty cell chamber using the FlowTrac ll unit The total volume of water required to fill up the standard model 3440 permeability chamber is about 2500 cc and the total volume capacity of the FlowTrac ll unit is 250 cc The easiest and most practical way to fill up the permeability chamber is to do so directly from the water faucet Note Except when running Ko consolidation there is no particular requirement for the quality of the chamber water as long as the water is potable 3 Q Do I need to use de aerated water to fill the FlowTrac Il units if so how do obtain de aerated water A Yes it is important to use de aerated water to minimize air bubbles in the system and speed up the back saturation process To prepare de aerated water boil water while Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 PERM MS User s Manual 2013 Geocomp Corp applying a vacuum or use a device such as a Nold DeAerator which combines propeller cavitation with a vacuum to de aerate the water rapidly 4 Q How can I change the rate at which the pumps fill during 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 involves suction as a result the filling rate was determined so that it prevents cavitation from occurring 5 Q I am running a
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