DSS - Geocomp
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1. Consequently 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 controllers of the ShearTrac ll DSS unit To do this follow the steps shown below 1 Bring down the Calibrate menu and select Summary Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp SHEAR C Documents and Settings My File View Run fa Control Report Options Help a Summary a SIEN TestPars Yertical Load dation T able Vertical Displacement Horizontal Load ee oe Horizontal Displacement Maximum Delay Displacement min Machine mm Displacement 5 08e 003 6 35 Displacement 0 508 6 35 2 On the 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 Calibration Summary Channel fv ettical Load v Factor 0 1197415723642 N cnt Offset 132793 cnts Date s at 08 JUL 2006 09 25 30 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 each sensor You should now see that the PC and LCD screen values match 1 3 Q In2. Each porous stone is 6 4 mm or 0 25 in thick l 4 Q While running our ShearTrac II DSS we have noticed that the arm for our vertical displacement sensor is bumping into the rear four prong nut that holds the crossbar in position A At the start of a test while the crossbar is still swung to one side use the left hand keypad on the ShearTrac ll DSS front panel to initialize the vertical loading mechanism From the LCD main menu select the Position option choose Initialize then press the Ent key The loading mechanism will move to its highest position activate the upper limit switch and then move down about 3 mm 0 12 in Loosen the nut that clamps the LVDT arm to the vertical post and slide the arm up a ways Raise the LVDT shaft into the housing and use a piece of tape to hold it in the raised position Swing the crossbar into position Now lower the LVDT arm until its underside is about 6 to 10 mm 0 25 to 0 4 in above the rear four prong nut Remove the tape and lower the LVDT shaft onto the crossbar If necessary adjust the horizontal position of the LVDT arm so that the shaft is midway between the sides of the crossbar It is best to raise the shaft slightly while doing this to avoid having it catch on anything and damage the LVDT There should now be clearance even when the loading mechanism is a high as it will go Il LIMIT SWITCHES Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0
3. 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 SHEAR DSS 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 Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp Note The raw data and the results of data reduction shown on the report pages will be changed The stress target values that were entered into the Consolidation Table page will not be changed Il CONSOLIDATION PHASE Il 1 Q noticed that for some very soft soil it takes longer than one second for the vertical load to reach the specified load during the consolidation phase Why does it do that A The rate at which a load is applied is controlled by the PID Proportional gain Integral gain and Derivative gain parameters They are shown on the Load PID Settings window that is opened by selecting PID from the Options menu Both the Proportional Gain P Gain and Integral Gain I Gain affect the overall rate at which the target load is reached but
4. 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 SHEAR DSS program so that they can be displayed on the various SHEAR DSS 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 the Graph Table Settings and Edit options all activated Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR 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 VI SHEAR PHASE VI 1 Q During the shear phase noticed that my displacement rate is slightly different than the one that specified in the Shear Table Why is that How can set it up correctly A If the first and fifth columns headed Ela
5. DSS hardware manual In each of Sections 2 1 4 and 2 2 4 Setup sections 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 unit were changed because you are controlling more than one unit with your computer set them to the values they were changed to The default values are 101 for vertical control and 102 for horizontal control Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp Software 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 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 0 001 KN 0 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 s
6. Step Multiplier value that is now needed for your ShearTrac Il DSS frame 1 Open the System Monitor window select System from the View menu and so that you can view the reading from the horizontal LVDT 2 Move the water bath box left or right until the horizontal displacement transducer reads about 15000 counts as seen in the left hand text field fourth from the top on the System Monitor window Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp 3 Record both the Horizontal reading in mm or in and the Pulse Count for the Horizontal Motor Note that the Pulse Count is the motor step count 4 Now move the water bath box until the horizontal displacement reads about 45000 Again record both the Horizontal reading in mm or in and the Pulse Count Calculate the Load Step Multiplier as follows 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 Step Multiplier value for the Horizontal Motor with the one you have calculated Then click the Apply button au VI 2 Q The ultimate shear values match closely The maximum shear is a little off 36 5 according to Geocomp Corp 38 7 according to us Do the maximum DSS results suggest that the discrepancy is in the level of compaction We installed the sand in one dry layer and tamped lig
7. for 1 65 minutes at which time we realized that it was not running at the desired rate We then proceeded to enter in the desired rate as step 2 in the shear phase and told the program to go to the next step which it did with no problem We were then running at the desired rate for the remainder of the test Our problem comes in that we cannot get the report function to load step 2 of the shear phase so our report is noting 1 65 minutes to failure at a maximum shearing load of around 8 psf This is not the correct data and therefore does not lend itself to the phi angle and cohesion calculations necessary for what we are doing Is there a way to get the program to accept ALL of the shear data or at least the 2nd step so we can use the report function This data is saved as part of the file as we can view it in table format A The report feature of the SHEAR DSS software does not show the graphs for each shear step on separate pages as it does for the consolidation phase Instead each graph on the second two pages plots the result of all the steps To view the graphs having all the steps on them bring down the report menu highlight Graph and choose Shear Then click View upper left corner of the window and choose Next Page V 3 Q I noticed that Mohr circles are plotted on some results in your manual Is it correct to draw Mohr circle from the DSB results A Yes you could draw Mohr circles from the direct simple shear tests V 4 Q
8. in somewhat different ways An increase in value increases the rate a decrease in value decreases the rate The possible value range for P Gain is from 0 5 to 5 and will change the loading time by about a factor of 3 from the lowest value to the highest While the default values 2 for P Gain and 1 for I Gain are appropriate for most soil types it may be helpful to increase the P gain to a maximum of 5 for a very soft soil specimen The I Gain should not be changed To change the P Gain setting select PID from the Options menu to open the Load PID Settings window Change the Proportional Gain setting to a higher value click the Apply button and then close the window Il 2 Q The responding time for the loading in the consolidation seems a bit slow we tried to load from 5 to 10kPa took about 6 7 seconds I don t think it s a big problem for direct simple shear but it may be not as good when we use the machine for consolidation tests as we are testing a lot of silty materials A According to Section 6 0 of ASTM standard D 2435 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 than 2 s During the consolidation phase the T100 value is shown on the Test Monitor window opened by choosing
9. 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 Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp 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 y 0 0127x 0 1328 R 1 E E c 6 E 6 O S 2 2 a From Micro Steps e From Displ Sensor 600 700 Time minutes Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266
10. phase Then you can use the table to find the recommended displacement rate Or you can use the table to get an estimated value for the Failure Deformation DF and then use the equation The easiest way to get the T90 value for a consolidation phase step is by dividing T100 by 1 5 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 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 Example Dense sand with a T90 equal to 5 min From the table the recommended displacement rate 0 0008 in min because the dense sand column shows this value for a T90 of 5 min From the equation the recommended displacement rate 0 05 in 50 x 0 25 x 5 0 008 in min because the table gives a DF of 0 05 in for dense sand Note K H Head has a discussion on this subject in Volume 2 of his Manual of Soil Laboratory Testing Pentech Press 1994 In the Second Edition this is in section 12 7 on pp 247 He includes a table of recommended deformation failure values which depend on the type and density or stiffness o
11. the Load 4 Repeat the above steps as the test progresses Ill 3 Q What is the area correction for a round sample A As the shear phase proceeds soil to soil contact area reduces The correction is calculated using A FA where A corrected area F area correction factor Ao Original sample area For a circular sample the area correction factor is 2 F 2 cog Ah Ah i Ah m D D D where Ah horizontal displacement D sample diameter It is best to calculate the internal friction angle based on the ratio of horizontal load to vertical load instead of shear stress to normal stress to eliminate the area correction and any related correction Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp Ill 4 Q Is it possible to take into account the effect of the top cap s weight when running a shear test A Yes by increasing the offset value to match the resulting vertical force due to the weight of the top cap The following steps will guide you through doing this 1 Weigh the top cap and record the value 2 Open the Calibration Summary window Summary option on the Calibrate window and note the Factor value for Vertical Load 3 Divide the weight of the top cap by the Factor value This will give the count equivalent of the weight Be sure the weight unit for the factor is the same as the unit used when weighing the top ca
12. 1 in horizontal displacement See attached What could a be the reason Maximum A This could be attributed to something mechanical getting in the way at about the 2 5 mm mark Check the gap in the shear box to be sure the two halves of the box are free to move relative to each other Check the region around the bath box to be sure nothing is close to it under the water bath box to be sure there nothing there that might hinder its movement VI 8 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 3080 the rate should be maintained with less than 5 of the target value See section 6 4 2 below 6 4 2 Device for Shearing the Specimen The device shall be capable of shearing the specimen at a uniform rate of displacement with less than 5 percent deviation and should permit adjustment of the rate of displacement from 0 0001 to 0 04 in min 0025 to 1 0 mm min The rate to be applied depends upon the consolidation characteristics of the soils see 9 12 1 The rate is usually maintained with an electric motor and gear box arrangement and the shear force is determined by a load indicating device such as a proving ring or load cell 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
13. 12 7 mm 0 5 in 10 When you are satisfied that everything has been adjusted correctly use the View menu on the SHEAR DSS control window to open the System Monitor window Adjust the physical position of the horizontal displacement sensor until the Horizontal reading on the System Monitor window is 32767 counts this is half the maximum reading of 65535 counts 1 3 Q We are running out of travel during consolidation The soil is an organic peaty material It appears that the maximum vertical travel is 12 7 mm 0 50 in How can we solve this problem There are two possible solutions for this problem First after you have swung the crossbar into position use the Initialize option on the left hand LCD Position menu to start the loading mechanism near its highest position Then use the nuts on the vertical threaded rods to lower the crossbar until the load cell button is close to the stainless steel ball This will provide the largest possible downward travel If there is still not enough travel you will need to reduce the thickness of your sample But you have to maintain the conditions that the shear plane is midway between the top and bottom of the sample that there are porous stones on both ends of the sample and the top cap is the same height above the bottom of the shear box A way to do this is to use two porous stones at the bottom of shear box a sample that is 12 7 mm 0 5 in high and two porous stones on the top of the sample
14. 266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp Il 1 Q The crossbar moves up at the beginning of the test until it triggers the upper limit switch Then the test stops and an error message appears on the screen indicating that the upper limit switch is on Why is this happening A This occurs if at the start of a test the load cell is registering a load that is greater than the target value for the first incremental consolidation step To ensure that this does not happen always zero the load cell before starting a test See Section 6 2 for the zeroing procedure Il 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 action you take depends on whether a vertical or horizontal limit switch has been triggered Check the ShearTrac Il DSS front panel to see which limit switch is blinking Vertical limit switch If the lower limit switch is triggered during the consolidation phase it will have to be adjusted if you want to continue with the test However this involves opening up the load frame We recommend that you abort the test When you start a new test initialize the vertical load mechanism then use the nuts on the vertical threaded rods to lower the crossbar Set it so that there is only a small gap between the load cell button and the stainless steel ball Horizontal limit switch Identify which horizontal limit switch left or right has bee
15. DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp Frequently Asked Questions Hardware I GENERAL l 1 Q The J og choice from the Position menu for manual horizontal control of ShearTrac Il DSS does not seem to work have been pressing the arrow up and down without any response The vertical movement works A It is necessary to push the left and right arrows when using the Jeg choice for horizontal control l 2 Q How does the horizontal initialization work A The horizontal initialization is a very useful option because it allows you to automatically reset the shear box so that the water bath box is in the middle of its motion range and the stainless steel ball is aligned with the vertical load cell button But it will work only if the limit switches and water bath box have been set in the correct positions To set the limit switches and water bath box in the correct positions use the following steps 1 Loosen the left four prong nut that is used to fasten the threaded rod that goes from the horizontal load cell to the positioning bracket and screw it all the way to the load cell Slide the shear box piston to the right as far as it will go 2 Assemble shear box and position it securely in the water bath box Be sure there is gap between the end of the shear box piston and the fastening plate on the right side of the shear box upper half 3 Put something in the shear box that is about the height of a sample plus porous s
16. Test Monitor from the View menu But you need to wait until the test is well into the step before using 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 Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp While the default values 2 for P Gain and 1 for I Gain are appropriate for most soil types it may be helpful to increase the P gain to a maximum of 5 for a very soft soil specimen The l Gain should not be changed The table below gives three P gain values that often work well for the range of sample stiffness shown Recommended P Gain Sample stiffness value LOOSE VERY SOFT 5 0 MEDIUM SOFT MEDIUM 2 0 DENSE STIFF 0 5 To change a PID setting select PID from 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 Il 3 Q How do I increase the responding time for the loading in the cons
17. The values of these parameters that will produce the most rapid loading rate while preventing the target from being hit too rapidly differs for each soil type The default values of 2 and 1 for the P Gain and l Gain respectively work well for most soil types The graphs that are included in the answer to Q A IV 1 above help to show the effects of the P Gain and I Gain As can be seen the I Gain needs to be changed only for very stiff soils 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 change it to negative 0 2 it will change In this particular case the default Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp 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 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 We are having a problem running the report on one of our tests and was hoping you could offer your insight on the situation The shear phase of the test was started and ran
18. dicated to consolidation and swell testing that has full reporting options However that program is designed to run tests ona LoadTrac ll DSS system and will not run a test on ShearTrac ll DSS If you plan to be doing a lot of full consolidation tests you should consider purchasing the LoadTrac ll system with the ICONP software Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp lll GENERAL Ill 1 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 values for sample dimensions calibration factors and PID control parameters 2 Zero values for sample dimensions calibration 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 The ShearTrac ll DSS load frame not turned on Ill 2 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 and click on Load 3 Go tothe Report menu You will be able to see the partial test results up to the point when you did
19. e step As soon as the SHEAR DSS 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 select PID from 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 IV 2 Q What are the effects and correlations between the PID values A The SHEAR DSS program uses a control technique that is very complex Consequently it is difficult to explain in detail how the PID values are used In general terms as an applied load is reaching its target value during the consolidation phase the program periodically gathers information and adjusts the loading rate by using the information and the PID Proportional gain Integral gain and Derivative gain values Both the Proportional Gain P Gain and Integral Gain I Gain affect the overall rate at which the load reaches the target value but in somewhat different ways An increase in value increases the rate a decrease in value decreases the rate As the load gets close to the target value the P Gain functions to decrease the loading rate so that the target value is not reached too suddenly Keeping the loading rate constant would be like hitting the specimen with a hammer On the other hand I Gain functions to increase the loading rate throughout the loading process
20. elect 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 Monitor 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 This zeroing process cannot be applied to the horizontal load cell See Section 6 2 2 for the horizontal load cell zeroing procedure l 2 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 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 SHEAR DSS 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 controller of the ShearTrac Il DSS unit However the software uses only the Calibration Summary values when it runs a test
21. eocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp Ill 2 Q The Network LEDs are RED on the front panel and there is no communication between the PC and the ShearTrac II DSS 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 IV POWER OUTAGE IV 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 ShearTrac ll DSS unit 2 Wait about 10 sec 3 Turn it 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 ShearTrac ll
22. f soil The range is from about 5 to 8 mm 0 2 to 0 3 in for loose sands 2 to 5 mm or 0 08 to 0 2 in for dense to about 1 to 2 mm 0 04 to 0 08 in for hard clay 2 to 5 mm or 0 08 to 0 2 in for stiff He recommends 8 mm 0 3 in for plastic clay Bill Kovacs Holtz and Kovacs notes that about 0 2 inches is adequate for most specimens about 5 mm If you are inexperienced with this soil type it is probably best to err on the side of caution and use a lower estimate of the deformation failure value giving a slower displacement rate Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp VI 4 Q Some clients require a multi stage direct simple shear test For this they want three different normal loads on the same specimen After each consolidation the shear phase is to be run Is it possible to program all this in a single file A First it is important to know that we do not recommend running a Shear Maximum Maximum multi stage shear test by usi ng either Control Rate Displacement Force ShearTrac Il DSS or the Triaxial min mm IN system that comprises LaodTrac Il Displacement 6 08e 003 6 35 890 and FlowTrac ll There is considerable Displacement 0 508 6 35 850 question about quality of the Displacement 0 508 6 35 890 Displacement 0 508 6 35 890 undisturbed soil sample when it is brought to t
23. he vicinity of shear failure then reconsolidated to be sheared again Furthermore there is no standard that we know of that is related to this test We do understand that in some special cases when there is a very limited amount of the soil sample there is justification in using a multi staged test This way you can get a complete set of three tests to generate Mohr Coulomb failure and hence determine conservative strength parameters for the sample that never reaches full failure Currently the SHEAR DSS program will not run a multi stage direct simple shear test in one single file You can however combine the data from the three files into one set of data using a spreadsheet program such as Excel You can either use the Dump option from the File menu or copy the data from the table opened using the Table option from the Report menu See Appendix B of this manual for details VI 5 Q We 5had a client asking for some special direct simple shear tests They call them constant stiffness tests o e constant and I believe ShearTrac II DSS is capable of doing this We may need a special control program and would like to have your help with this A In theory ShearTrac IIl DSS should be capable of running this special test However we would need a customized control software program not currently available with an entry for constant stiffness Then the program would vary both the vertical load and the vertical displacement as needed to
24. htly to form a smooth surface A The internal friction angle is directly proportional to the void ratio of the sand or relative density so it is not surprising that the two values differ by couple of degrees The correct compaction is difficult to duplicate VI 3 Q Do you have any recommendation for the displacement rates that we should use for the shear phase A The best displacement rate depends on what testing standard is used so you should check the standard you are using to see if there is a recommendation The information below includes a table that has been prepared for Geotesting Express and an equation used by them Recommended Displacement Rates in in min CLAY Very Stiff Stiff Medium Soft Failure Deformation Df in 0 02 0 05 0 1 0 15 Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp T90 min Shear Rate in min 0 5 0 00320 0 00800 0 01600 0 02400 1 0 00160 0 00400 0 00800 0 01200 5 0 00032 0 00080 0 00160 0 00240 10 0 00016 0 00040 0 00080 0 00120 20 0 00008 0 00020 0 00040 0 00060 30 0 00005 0 00013 0 00027 0 00040 60 0 00003 0 00007 0 00013 0 00020 Displacement Rate in min Df 50 x T50 Df 50 x 0 25 x T90 You will need to know the type of soil you are working with and the T90 value the time for 90 primary consolidation that can be determined during the consolidation
25. keep the specified stiffness constant throughout the consolidation phase Similarly when the shear phase is run the vertical load would be varied so that a constant height of the sample would be maintained Since the area does not change this would result in keeping the volume constant The resulting change of vertical stress Ao is indirectly equated to the change of excess pore pressure Au VI 6 Q In what unit is the shear rate The software program shows the Rate as min with no unit in the numerator Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp A The unit for rate depends on the Shear Control parameter you have chosen If you have chosen Displacment the rate is mm min or in min for the metric or English choice of units see first example at right if you have chosen Force the rate is N min or lb min for the metric or English choice of units see second example at right If you wish you can choose a different unit for time The choice of units is made on the window opened by selecting the Units item on the Options menu Then the heading in the Rate column would show chosen time unit and the rate would be either Distance chosen time unit or Force chosen time unit depending on the choice in ghe Shear Control column VI 7 Q have been getting a consistent jump in the shear stress curve at around 2 54 mm 0
26. l 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 l 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 in the consolidation phase 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 Sample stiffness value LOOSE VERY SOFT 5 0 MEDIUM SOFT MEDIUM 2 0 DENSE STIFF 0 5 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 consolidation test They were 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 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 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 bo
27. 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 SHEAR DSS 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 the test was set up The two possibilities are described below The parameters are correct You have two ShearTrac Il DSS units A and B You plan to run a test on unit A A file for a test run on unit B is a good template for the test but the calibration parameters in it are Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp those for the sensors on unit B You open a SHEAR DSS control window and load that file into the window We will call that file Test B Next you open a second SHEAR DSS control window and load into it a file for a test that was run on unit 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 Summa
28. n triggered Move that switch away from the point of contact by about 0 65 mm 0 25 in Once the triggered switch has been moved the ShearTrac ll DSS front panel light will stop blinking Click OK on the error message window and restart the test Before you start the next test we recommend that you reset both horizontal limit switches so that the horizontal initialization using the keypad and the Position menu on the right LCD works correctly See Question l 2 in the Hardware section of Appendix F lll NETWORK COMMUNICATION Ill 1 Q We have several systems connected to the same PC We were running only one of the systems so we shut off the ones we were not using Then we got an error message stating that the system 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 should be back to normal G
29. olidation A The rate at which a load is applied is controlled by the PID Proportional gain Integral gain and Derivative gain parameters They are shown on the Load PID Settings window that is opened by selecting PID from the Options menu Both the Proportional Gain P Gain and Integral Gain I Gain affect the overall rate at which the target load is reached but in somewhat different ways An increase in value increases the rate a decrease in value decreases the rate The possible value range for P Gain is from 0 5 to 5 and will change the loading time by about a factor of 3 from the lowest value to the highest While the default values 2 for P Gain and 1 for I Gain are appropriate for most soil types it may be helpful to increase the P gain to a maximum of 5 for a very soft soil specimen The l Gain should not be changed To change the P gain setting select PID from the Options menu to open the Load PID Settings window Change the Proportional Gain setting to a higher value click the Apply button and then close the window Il 4 Q We just ran a full consolidation test and direct simple shear cannot find the consolidation test report to view the graph and data for the consolidation part of the test Do we have the software to produce a full consolidation test report and I m just not finding it A The report for the shear phase of a test shows only time displacement data and graphs There is another software program ICONP de
30. p 4 Open the System Monitor window System option on the View menu and note the count value for Vertical load top left text field Determine the sum of this value and the count value found in step 3 5 On the Calibration Summary window replace the Offset value for vertical load with the value obtained in step 4 Click the Apply button and then the Download button You will now find that the engineering unit reading of the vertical load cell shown on the System Monitor window top right text field will be the weight of the top cap when the load cell is not in contact with anything Ill 5 Q Could you explain to me why the values for the same items are different in the System Monitor window on the PC screen from those in the System Monitor shown on the ShearTrac Il DSS LCD screen A The values shown in the top four text fields on the PC System Monitor window come from the application of the calibration parameters shown on the Calibration Summary window to the output of the sensors The corresponding values on the LCD screens come from the application of the calibration parameters that have been downloaded into the ShearTrac ll DSS imbedded controllers If parameter values on the Calibration Summary window have been changed but not downloaded to the imbedded controllers by clicking the Download button values on the PC System Monitor window will be different from those on the LCD System Monitor The entries in the Vertical Motor and Ho
31. psed Time and Horizontal Displacement 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 DIRECT SHEAR TEST DATA Location Tested By jdt Test Date 07 14 06 Sample Type cylinder Soil Description Ory dark gray claystone Remarks Vertical Horizontal Horizontal Displacement Stress Displacement in psi in 0 01144 0 2423 0 0 01144 0 2769 1 678e 005 0 01144 0 2769 0 0 01144 0 3115 0 0 01144 0 g The two factors that determine how close the actual horizontal displacement rate is to the value specified on the Shear Table are the horizontal displacement transducer calibration factors and the Step Multiplier for the horizontal motor 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 Step Multiplier that depends on the characteristics of the ShearTrac Il DSS 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
32. rizontal Motor text fields are sent to the PC from the ShearTrac ll DSS imbedded controllers and will always be the same as those on the LCD screens For running a test it does not matter if the values are different The test is run using the calibration parameters that are on the Calibration Summary window So as long as those are the correct values the test result will be accurate To avoid having different values on the PC and LCD screens always click the Download button after making any change on the Calibration Summary window Note that only the parameters for the sensor shown in the top text field will be sent to an imbedded controller To insure that all displays will be the same download the parameters for each sensor one by one Ill 6 Q What is the definition for the failure condition in a direct simple shear test Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp A According to ASTM standard D 3080 Failure is often taken to correspond to the maximum shear stress attained or the shear stress at 15 to 20 percent relative lateral displacement Depending on soil behavior and field application other criteria may be defined IV PID SETTINGS IV 1 Q The User s Manual says that the Proportion Gain on the Vertical Load PID Settings window can be as high as 5 for soft soils and as low as 0 5 for stiff soils Also the Integra
33. ry in Test A You now have a control program that contains the correct calibration parameters for running a test on unit 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 ShearTrac ll DSS units A and B You plan to run a test on unit A A file for a test run on unit B is a good template for the test but the calibration parameters in it are those for the sensors on unit B You open a SHEAR DSS 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 Calibrate window But you forget to click the Save button on each window before closing it 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 SHEAR DSS 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
34. th the l Gain and P Gain can be decreased Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp Very Soft Soil Modulus 290 psi PID 0 5 1 0 PID 5 1 0 Load Target 2 0 25 3 0 3 5 4 0 Time min Time min Medium Soil Modulus 4000 psi PID 0 5 1 0 PID 5 1 0 Load Target 0 00 0 05 0 10 0 15 0 20 0 25 030 035 040 0 45 0 50 0 00 005 O10 0 15 020 025 030 035 040 045 0 50 Time mi n Time mi n Stiff Soil Modulus 10 000 psi PID 0 1 0 1 0 PID 0 5 1 0 Load Target gt gt gt Load Target ro 0 10 0 15 0 10 0 15 Time mi n Time mi n Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp In addition a rule of thumb for response time is given in Section 6 0 of ASTM standard D 2435 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 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 th
35. tones and will be able to support the top cap in its normal position Place the top cap into position and place a stainless steel ball on the top cap 4 Swing the crossbar into position tighten the two four prong nuts and lower the crossbar until the vertical load cell button is slightly higher than the top of the ball 5 Use the horizontal key pad and J og option from the Position menu for horizontal control to make a careful alignment of the top of the ball and the center of the load cell button 6 Carefully measure the distance between the left limit switch and the left side of the water bath box Position the limit switch so that the distance is exactly 12 7 mm 0 5 in 7 Choose the Initialize option from the Position menu for horizontal control and press Ent The water bath box will move to the left until it triggers the limit switch The step count will be zeroed and the water bath box will move to the right exactly 12 7 mm 0 5 in 8 Check to see if the ball has stopped directly below the center of the load cell button If it has not reposition the left limit switch and repeat the initialization until the ball stops with correct alignment Geocomp Corporation 125 Nagog Park Acton MA 01720 Tel 978 635 0012 Fax 978 635 0266 DIRECT SIMPLE SHEAR TESTING 2013 Geocomp Corp 9 Measure the distance between the right side of the water bath box and the right limit switch Adjust the right limit switch so that the distance is
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