IST - CRS

CRS Cell Assembly Handbook

Introduction

The GDS Interface Shear Tester (IST) uses continuous rotation providing an alternative option to a multiple reversal interface shear test. Infinite shear deformation can be applied to the sample, allowing the determination of ultimate friction angle values. Cyclic (not dynamic) loading can be performed to simulate the action of loadings with alternating directions. It is a self-contained stepper motor-driven unit that can be controlled either manually using a Smart Keypad, or from a PC via the USB interface.

This handbook provides the user with a guide to the GDS IST, covering the following aspects of the system:

• Set up of the system hardware

• Set up of the system software

• System operation via the Smart Keypad

• System operation via the GDSLab software

System hardware

The standard GDS IST is comprised of the following hardware devices:

• GDS IST load frame with 5kN-200Nm DBBSS load cell (Other sizes available on request)

• 2 x 24 VDC power pack, 2 x IEC mains leads (with user-specific plug), and 2 x USB cables

• Smart Keypad

• Optional +/- 12.5mm external displacement transducer, connection either:

  • via serial pad (data logger)

  • via Digital Remote Feedback Module (DigiRFM)

• Optional cell types (38mm up to 112.8mm) 

System software

The GDSLab software is used to automate the testing process for determining the torque generated between the specimen and test material. This requires the use of the following GDSLab test module:

• Standard Consolidation Module (Consolidation/Rowe/CRS/IST)

System features

• Self-contained unit with no requirement for reversal testing

• Automated consolidation and rotational testing via GDSLab control

• Simple USB interface to PC for both the GDS IST load frame axis

• Cyclic (not dynamic) loading

Important information

*The system should be set so that any external displacement transducer that is fitted will not reach full travel before the axial extension is reached. This is either in axial loading or axial displacement control. Failure to observe this could result in damage to the displacement transducer.

Setting up the System

The GDS IST is initially installed by completing the procedures listed in the hardware and software sections below. 

Setting up the GDS IST hardware

Step 1 – Remove the GDS IST load frame from the shipping crate. The frame will be packaged with the control boxes separate and any additional items such as the cell will most likely be in separate boxes.

GDS IST

Step 2 – Remove the Smart Keypad from the packaging and place it on the front mounting bracket. This is held in place with the magnetic strip attached to the top of the controller and the strip magnet attached to the back face of the Smart Keypad.

Step 3 – Attach the keypad cables to the RFM (optional: only if it’s attached to the side and part of the order) The Axial Control Keypad connects to the Displacement RFM and the Radial Control Keypad connects to the Pore Pressure RFM. The back of RFM has two CAN cable connections, it doesn’t matter which one is used for the keypad and the IST.

Rear Connections

Example Connections

Step 4 - Following the previous two figures above, plug in:

• The load cell connectors (color match)

• IEC main lead connector

• CAN cables from the RFM(s) (optional: only if it’s part of the order) or keypads

• USB connectors to/from laptop

Step 5 – If an additional transducer is being used via an RFM please see section Appendix A: Smart Keypad Functions on using an RFM.

Step 6 - Secure the load cell and the shearing interface top cap with the Mechalock fittings. To do this first set the Mechalock in place and tighten by hand. Once the parts are holding in place they need to be tightened up using a 41mm spanner.

Load cell connection (left) and IST top cap (right)

Setting up the GDSLab software

Step 1 – Open the GDSLab handbook (either hardcopy or in .pdf format) supplied with the system and follow Section 2 to install the latest version of GDSLab on the PC.

Steps 2 – Connect the USB leads to the test PC and then switch the power on the IST. This will enable the USB drivers required to communicate with the load frame to automatically finish installing on the PC.

Step 3 – Launch GDSLab and create a new station (or stations if using more than one GDS IST) using the .ini file (e.g. “GDS IST.ini”) supplied with the GDSLab USB. The alternative ini file is “GDS IST DigiRFM Displacement.ini” (or similar) if the order has RFM(s) attached.

Selection of .ini file within GDSLab.

GDSLab Object Display showing GDS IST load frame

Step 4 – Open the ‘Object Display’ and click on the GDS IST Load frame image for the appropriate axis. This will display the Controller selection tool, which enables connection to the control box based on the selection of the GDS serial number (these can be found on the back of the control boxes). To select the appropriate control box click on the serial number associated with the axis.

Step 5 – Click on the ‘TX/CP’ button at the top of the ‘Object Display’ window, then on the ‘Read’ button to display the transducer readings from the GDS IST. If the values correspond (and have a blue font) to those on the Smart Keypad, the system has been successfully set up. Otherwise, create a support ticket on our website.

Operating the System 

The GDS IST can be operated via two control methods: manually using the Smart Keypad, and automated control via the GDSLab software. To conduct a test, both methods are generally used, as the Smart Keypad allows the physical system to be set ready for testing, whilst GDSLab automates the test load/displacement control and measurement.

Smart Keypad control

The Smart Keypad front panel is presented in the figure below with labels showing the primary display features.

Smart Keypad front panel and display

The system can be operated via the Smart Keypad through the use of a number of menus and keypad buttons. A complete guide to this functionality is given in Appendix A, however, the most basic and useful functions are listed in the following:

• Unlock Keypad – To unlock the Smart Keypad to regain manual control after operation via PC, press (./-), (↵), (2), (↵), (↵)

• Target Load / Torque – To apply a specified load to the test specimen press (CMD) > (7), then type the required load value (in kN/Nm) using the numerical keypad. To begin the load application press the green ‘Enter’ button (↵)

• Target Displacement / Angle – To move the ram or cell to a specified position press (CMD) > (4) then type the required displacement value (in mm/degrees) using the numerical keypad. To begin movement press the green ‘Enter’ button (↵). Note the targeted displacement is based on the internal displacement reading, with positive readings corresponding to the ram moving downwards and the platen rotating anti-clockwise.

Setting a load target of 0.5kN (left) and displacement target of 1.5mm (Right)

• Apply Load Offset – To set the load reading to zero by applying a soft zero offset press (CMD) > (CMD) > (8) > For reapplying an offset (↵) will need to be pressed after the previous commands.

• Remove load offset – To remove a previously set soft zero offset on the load reading press (CMD) > (CMD) > (9) > (↵)

Setting a load soft zero offset (left) and removing the load soft zero offset (right).

• Zero Displacement Reading – To set the internal displacement reading to zero press (CMD) > (CMD) > (5) > (↵)

• Ram Extension / Positive Rotation – To move the ram upwards or to apply positive rotation at a slow rate press (5) > (↵)

• Ram Retraction / Negative Rotation – To move the ram downward or to apply negative rotation at a slow rate press (2) > (↵)

• Stop Targeting of Load / Displacement – To halt the ram/platen movement when targeting either load or position press (Stop)

GDSLab software control

The following describes the procedure for automating both consolidation and rotational tests using the GDS IST and GDSLab software.

Step 1 – Load GDSLab and corresponding system .ini file. The Object Display may then be opened to check all transducers (‘Load’, ‘Displacement’, ‘Torque’, and ‘Degrees’) are reading correctly, or used to target load and displacement values.

GDSLab Object Display showing load and displacement readings

Step 2 – Ensure a small seating load has been applied to the test specimen, then close the Object Display. After entering the necessary ‘Data Save’ parameters into the ‘Test Plan’, click the ‘Sample’ button. At this point, the ‘Consolidation’ specimen type should be selected, followed by the Test Standard used in your region and specimen details (including initial height and diameter).

Selection of the ShearBox specimen type

Step 3 – Click on the ‘Add Test’ button and select the ‘GDS_hhStd_1h_Consolidation’ test module. The ‘Create New Test Stage’ button can then be used to specify the first stage of the specimen test. Instructions on how to reach the rotational settings are set out below:

• Select the test type the most appropriate for the current stage in the test. Fill in the test values and then proceed to the next window. (The first stage will most likely be a saturation stage for a closed-cell system or a consolidation using constant stress for an open system).

• Enter any termination settings required for the test and proceed to the second termination condition window

• Apply any extra termination conditions required for the test in the top section of this screen. A time limit can also be entered in the lower section of this window. The middle section is for use when the displacement is required to be set to zero at the start of a stage (e.g. when shearing is to start after the consolidation stage is completed).

• Having selected the option to show the additional options the following screen will show the options for pore air pressure in the upper section and the rotational control in the lower section.
  The options for rotational control on this system so far are as follows:

  • No Control – Used when only vertical loading is required

  • Target Zero Torque – Used when vertical loading may apply rotational movement to the specimen. (This may occur during consolidation and by targeting zero torque the rotational loading effects can be limited)

  • Rotational Displacement Rate – Used as a shearing rate in the rotational axis.

• Once all the details have been entered the stage can be added to the test list

Step 4 – Once at least one test stage has been created, the ‘Add To Test List’ button may be clicked and the ‘Go to Test’ button used to load the ‘Test Display’, allowing the test to be started.

GDSLab Test List with one saturation test stage prepared

Step 5 – The test data file should be accessed following completion of the test.

Setting an additional transducer as the Control Source

The IST control box has the option to add a ‘Remote Feedback Module’ to the system - which essentially adds another transducer to the Controller to be logged by GDSLAB. 

For instruction on changing between either Axial load or Torque and an additional transducer as the primary control source, see the ‘DigiRFM Settings’ section in Appendix A.

A typical setup would be to add a DigiRFM with +/-5 or 10mm Displacement Transducer to the Axial Control. This will allow a much more direct measurement of the axial deformation. It can also then be set to control via this additional transducer.

Optional Cell Designs

Open Bath Cell

Below is an example of an interface shear cell. The cell is an open-top cell and does not have any pressure control (Such as cell pressure and backpressure). This cell has two ports in the lower section for drainage and a porous disc that sits above these ports in the bottom of the cell. One of the ports could be used for potential pore pressure measurement but this would be Specimen dependent. The force in this cell is applied through a middle ring. The internal and external sections are fixed in place and will restrain the specimen from deforming and extruding around the middle ring. The outer ring can be lifted this allows a visual aid for docking of the specimen. The outer ring can then be lowered and fixed into place once docking has been confirmed. The center section, middle ring, and outer ring are made of the interface material required for the test.

Cell with the outer ring in the lowered position (Left) Cell with an outer ring fixed in the upper position (Right)

CRS Style Confined Cell

The CRS style Confined Cell is suitable for pressures up to 1MPa and can accommodate specimen sizes from 38mm – 70mm, other sizes may be available upon request.  The specimen can be fully submerged with a suitable medium and pressure can be applied with a GDS Pressure Controller. The option to add an RFM to the controller will allow the system to log Axial Displacement from an external transducer and remove the need for an 8 Channel Data Acquisition Box. The specimen is installed with the use of the center ring which is also used as the cutting ring. The sections are built up around the center ring and held in place by the upper section which is then screwed down to the lower pedestal section.

The interface material is fixed to the top cap section built into the loading ram. This should be fixed in place using a suitable adhesive.

To connected and disconnect the cell from the load cell the torque nut should be untightened from the lower section of the load cell and upper section of the loading ram. The system can then be retracted until sufficient space is available to lift the cell top out from the system. To remove the cell top it is easier to have removed the four tie bars completely. To ensure the ram does not fall through the cell top upon removal and installation a ram clamp is provided and should be fitted in place.

The torque nut upon installation should be tightened sufficiently to withstand the torque applied to the specimen.

Generic interface testing application

The frame is versatile and can accommodate custom-made clumping arrangements to fit the purpose of a wide range of interface testing. Any combination of soil and/or rock, concrete, and any other construction material can be tested. The main rationale is that one part of the interface is clumped at the bottom of the axial actuator (top part of the interface) and the other part is placed on the rotational actuator (lower part of the interface). If the interface partially consists of soil (especially non-cohesive), it is suggested that the soil specimen is placed on the rotational actuator. The steps that are usually followed in such tests are listed below.

• Use the ‘fast extent/retract’ command to bring the lower platen to the desired position before the initiation of the test. If high accuracy is required, the’ target position’ command shall be used.

• Use the ‘fast extend’ command to move the axial force actuator downwards and bring the top sample close to the bottom sample. Stop the actuator when a gap of around 5mm has been achieved. Note that the two parts of the specimen should not get in contact in this stage because high stresses might be induced and disturb the tested materials.

• Target a small load in order to dock the specimen. The load may vary depending on the type of the tested materials. However, a load of 2-3 N should be appropriate for soft samples.

• Set a consolidation stage through GDSLab. The stage will terminate once the desired deformation rate has been achieved.

• Apply the desired normal stress. This is done by targeting a stress for the axial actuator.

• Start the shearing of the sample. This stage can either be, rotation or torque controlled.

Appendix A: Smart Keypad Functions

The table below lists the Smart Keypad buttons shown in the keypad figure above, along with their associated functions. To call up the functions displayed below each of the numbers (i.e. 0 to 9 and ./-), the selected button must first be pressed, followed by the green ‘Enter’ button(↵).

List of Smart Keypad buttons and their associated functions

Descriptions of each menu available to be accessed from the Smart Keypad are given in the following:

Command Menu – allows two pages of functions to be accessed quickly. The required function is called up by pressing the associated number.

Available Command Menu functions from the axial axis

• Target Load (7) – specify a load value (in kN) to be applied to the test specimen. (Axial Keypad)

  • Target Torque (7) – specify a load value (in Nm) to be applied to the test specimen. (Radial Keypad)

• Target Position (4) – specify a displacement value (in mm) for the ram. (Note this value refers to the internal displacement platten reading.) (Axial Keypad)

  • Target Angle (4) – specify an angle (in deg) for the platen. Note this value refers to the internal displacement reading. (Radial Keypad)

• Fast Extend (6) – move the ram downwards at a fast rate. (Axial Keypad)

  • Fast Extend (6) – rotate the platen anticlockwise at a fast rate. (Radial Keypad)

• Fast Retract (3) – move the ram upwards at a fast rate. (Axial Keypad)

  • Fast Retract (3) – rotate the platen clockwise at a fast rate. (Radial Keypad)

• System Menu (0) – open the System Menu. (Both Keypads)

• Apply LoadOffset (8) – apply a soft zero offset to the load reading. (Axial Keypad)

  • Apply TorqueOffset (8) – apply a soft zero offset to the torque reading. (Radial Keypad)

• Zero Pos Reading (5) – zero the internal displacement reading. (Both Keypads)

• Remove LoadOffset (9) – remove any soft zero offsets applied to the load reading. (Axial Keypad)

  • Remove TorqueOffset (9) – remove any soft zero offsets applied to the torque reading. (Radial Keypad)

• Set Speed (7) – set the maximum speed at which the ram can move. (Axial Keypad)

  • Set Speed (7) – set the maximum speed at which the paten can rotate (Radial Keypad)

Main Menu – allows the primary GDS IST menus to be accessed, which contains all sub-menus displayed in the figure below for the axial axis.

Main Menu and sub-menus for the axial axis

Set  Pos/Load menu  –  allows load/Torque and displacement/angle values to be targeted, and maximum ram/rotational speeds to be set.

• Set Load – specify a load value (in kN) to be applied to the test specimen. (Axial Keypad)

  • Set Torque – specify a torque value (in deg) to be applied to the test specimen. (Radial Keypad)

• Set Position - specify a displacement value (in mm) for the ram. Note this value refers to the internal displacement reading. (Axial Keypad)

  • Set Angle – specify an angle (in deg) for the platen. Note this value refers to the internal displacement reading. (Radial Keypad)

• Set Speed – specify the maximum speed (in mm/s) at which the ram can move. (Axial Keypad)

  • Set Speed – specify the maximum speed (in deg/s) at which the platen can rotate. (Radial Keypad)

• Reset Speed – resets the platen speed to the maximum allowable value. (Axial Keypad)

  • Reset Speed – resets the rotation speed to the maximum allowable value. (Radial Keypad)

Extend/Retract menu – allows the ram or platen to be moved/rotated at slow or fast speeds.

• Fast Extend – moves the ram downwards at the maximum allowable speed. (Axial Keypad)

  • Fast Extend – rotates the platen anticlockwise at the maximum allowable speed. (Radial Keypad)

• Fast Retract – moves the ram upwards at the maximum allowable speed. (Axial Keypad)

  • Fast Retract – moves the platen clockwise at the maximum allowable speed. (Radial Keypad)

• Slow Extend – moves the ram downwards at the speed set by the user within the ‘Set Pos/Load’ menu. (Axial Keypad)

  • Slow Extend – moves the platen anticlockwise at the speed set by the user within the ‘Set Pos/Load’ menu (Radial Keypad)

• Slow Retract – moves the ram upwards at the speed set by the user within the ‘Set Pos/Load’ menu. (Axial Keypad)

  • Slow Retract – moves the platen clockwise at the speed set by the user within the ‘Set Pos/Load’ menu. (Radial Keypad)

Offsets Menu – allows a soft zero offset to be applied to the load/torque reading, and a DigiRFM transducer if attached.

• INT Offsets – open to apply or remove a soft zero offset from the load cell reading.

• RFM0 Offsets - open to apply or remove a soft zero offset from an additional transducer reading (only possible when a DigiRFM transducer is connected).

INT Offsets Menu axial left (left) and RFM0 Offsets menu (right)

Ramp/Cycle menu – allows both load/torque and displacement/angle values to be ramped or cycled.

• Pos Ramp/Cycle – specify the parameters to ramp or cycle the applied displacement/angle

• Load Ramp/Cycle – specify the parameters to ramp or cycle the applied load/torque

Load Ramp/Cycle menu (left shows top section of menu; right shows bottom section).

To perform either a load or displacement ramp/cycle or a torque or angle ramp/cycle the following parameters must be selected:

• Wave type:

  • Ramp (+) = increases the load/torque or displacement/angle value linearly

  • Ramp (-) = decreases the load/torque or displacement/angle value linearly

  • Sine = varies the load/torque or displacement/angle using a sinusoidal waveform

  • Triangle = varies the load/torque or displacement/angle using a triangular waveform

  • Square = varies the load/torque or displacement/angle using a square-shaped waveform

• Datum: For Ramp (+) and Ramp (-) wave types, specify the load/torque or displacement/angle from which to begin the ramp function. For Sine, Triangle, and Square wave types, specify the load/torque or displacement/angle for which the cycling will center.

• Period: For Ramp (+) and Ramp (-) wave types, specify the time to move from the specified datum to the load/torque or displacement/angle target (as entered into the Amplitude setting). For Sine, Triangle, and Square wave types, specify the period of the cycle (i.e. time to complete one cycle).

• Amplitude: For Ramp (+) and Ramp (-) wave types, specify the load/torque or displacement/angle target relative to the datum (e.g. if the datum is set at 0.1 kN, and the amplitude is set at 1.0 kN, the ramp will move from 0.1 kN to 1.1 kN). For Sine, Triangle, and Square wave types, specify the amplitude of the load/torque or displacement/angle during cycling (e.g. if the datum is set a 0.0 mm, and the amplitude set at 1.0 mm, the cycle will move between -1.0 and +1.0 mm).

• Cycles: specify the number of load/torque or displacement/angle cycles to be applied to the test specimen (not required for Ramp (+) and Ramp (-) wave types).

• Phase:  set a  phase offset when cycling the load/torque or displacement/angle  (e.g. if a  +90 degree offset is specified when the datum is set at 0.0 mm and the amplitude 1.0 mm for a Sine wave type, the displacement cycle will begin from 1.0mm).

System Menu – allows the system settings and details to be accessed and altered.

System Menu (top left shows the top section of the menu; top right shows mid-section; bottom left shows the bottom section of the menu).

• Reset Menu – open to restarting the Smart Keypad or the attached control box load without powering off the system.

• Lock/Unlock  –  open to lock the  Smart  Keypad to prevent accidental keypad commands from being pressed, or unlock the Smart Keypad after locking or PC control has taken place.

• Limits Menu – open to view the system limits (maximum load = 5.1 kN; minimum load = -1.0 kN), reset the virtual end stops (these are triggered when the ram reaches its physical end limits), set user-defined load/torque and displacement/angle limits, and clear user-defined load/torque and displacement/angle limits.

• DigiRFM Settings – open to set the control source for the GDS IST Axis Depended.

The DigiRFM can be set as the primary control source instead of the 5kN load cell or the 200Nm load cell. In such a case all functions previously assigned to load/torque (e.g. CMD option ‘7’, ‘Set Load/torque’ etc.) are re-assigned to allow control of the additional transducer.

DigiRFM Settings menu (left) and Set Control Source sub-menu. To set primary control as an additional transducer (instead of the 5Kn-200Nm load cell), select ‘Set Control Source’, then choose ‘RFM0’.

• Diagnostics – open to view diagnostic information relating to the GDS IST and Smart Keypad.

• System Calibration – open to view details of the load/torque and displacement/angle calibration

details for the system

• Event Log – open to view or clear the system event log.

• Display Setup – open to view or alter the Smart Keypad display settings and time before screensaver becomes active.

• About – open to view information about the Smart keypad

• Factory Mode – open to restore the system to the GDS factory settings (requires an access key from a GDS engineer).

*For further advice regarding the GDS IST, please contact the GDS support team directly by:

• visiting http://gdsinstruments.helpserve.com/

• emailing support@gdsinstruments.com