EMDCSS

The GDS Electro-Mechanical Dynamic Cyclic Simple Shear System Hardware Handbook

Introduction

This handbook provides an outline of the design and implementation of the Electro-Mechanical Dynamic Cyclic Simple Shear (EMDCSS) system.  For additional details on system software please refer to the separate GDSLAB manual.

Suggested System Layout

Overview of Components

The EMDCSS system consists of the following major subsystems:

• Axial and Horizontal Electro-Mechanical Actuator Units

• Axial and horizontal motor drive units

• GDS Advanced Digital Control System V2 (AdvDCS V2)

• Long and short-range vertical displacement measurements

• Long and short-range horizontal displacement measurements

• Vertical force measurement

• Primary and secondary horizontal force measurement

• Optional high accuracy shear LVDT upgrade

• Optional pore pressure measurement

Dynamic control unit

The dynamic control unit inside the AdvDCS V2 control box interfaces to the PC via a USB connection. It provides closed-loop feedback for both the vertical and horizontal axis, eight channels of analogue to digital conversion, digital inputs and outputs and a quadrature counter. It also features a compliance estimation unit that adapts the control responsiveness on the softness of the sample.

The dynamic control unit runs with a control loop frequency of 1 kHz (1000 control loops per second). The compliance estimation unit runs at 5 kHz.

Setting up the System

Setting up the Computer System

A high-quality, high-speed PC is needed for overall system functionality. We recommend an i5 processor or better (or AMD equivalent) at least 8GB RAM and running a fully updated version of Windows 10 or later.

The AdvDCS unit is connected to the computer using a USB cable. Acquired data is stored locally on the AdvDCS and passed to the controlling computer by a separate communications process.

Please follow the instructions referred in the section “Calamari Drivers” in the helpsheet below to install the software.

Software

GDSLab

215 GDS Helpsheet - Installation of Dynamic Drivers

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This Helpsheet is to guide you through the installation of the GDS Unity and Calamari Frameworks for use with dynamic systems.

You will need Administrative Privileges in order to progress through these steps.

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Installing GDSLab

Installation of the drivers is quick and easy. You will need to start with a fresh installation of the latest version of GDSLab, as supplied with either your GDSLab CD or USB Stick. This can also be downloaded from https://www.gdsinstruments.com/information/software-downloads

Start by connecting your GDS supplied USB stick to any available USB port on your PC. If you were supplied a CD, insert this into your CD-ROM.

Make sure the GDS Security Dongle is unplugged from the computer whenever you install GDSLAB

Navigate to the drive using Windows Explorer and look for the ‘.exe’ file called ‘GDSLabSetup…’ or similar.

Run this file and follow the installation procedure.

You should always check the first 3 tick boxes in order to install the necessary drivers for GDSLab to become compatible with the GDS hardware.

If you are updating GDSLAB (i.e. a version of GDSLAB was already installed in the PC) then do not tick the option “Install GDS Dongle Drives”

Installing Dynamic Drivers

Installation of either Unity Drivers (ELDCS, USB Pad or RFM Control) or Calamari Drivers (AdvDCS Control) follows the same procedure, but with different files.

Before installing Dynamic Drivers, please ensure you have the latest Windows .NET framework. This can be downloaded from Microsoft. Failure to update can cause compatibility and stability issues.

Unity

In your supplied GDS USB Stick or CD, you should find a folder titled ‘Unity Files’ or equivilent. If the contents are in a zipped folder, you should extract this to a location on your computer.

The two important files to locate within these folders are ‘Deploy ToPlugins’ and ‘GDS.Unity/CleanRegistry’ files

1. Run the ‘GDS.Unity.CleanRegistry’ file.

2. Run the ‘DeployToPlugins’ File

You can safely allow the program to make and save changes to your computer.

You can ignore the registry editor warning panel

AdvDCS V2 (Calamari)

In your supplied GDS USB Stick or CD, you should find a folder titled ‘AdvCore Files’ or equivilent. If the contents are in a zipped folder, you should extract this to a location on your computer.

There is only one file you need to use in this install as the rest is performed automatically. It is titled ‘DeployToPlugins’

Double click on this file and ignore the warning message about it coming from an unknown source if it pops up. If windows user control it active you can also say ‘yes’ to ‘allow this program to save changes to your computer’

This file will automatically install the other files as seen here through the Command Prompt.

Once this is finished you can press any key to close the Command Prompt and run GDSLab.

Hardware

DYNTTS, EMDCSS

AdvDCS v2 User Interface

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This Helpsheet show the new GDSLAB graphical user interface for devices using the AdvDCS v2 (Calamari) Driver

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The AdvDCS v2 - Advanced Dynamic Control System was introduced in 2018 to replace the older DCS control unit on the new Dynamic Simple Shear (EMDCSS) and Dynamic Triaxial systems. Working together with a new iteration of motor drives the AdvDCS v2 provides more control and logging options for dynamic tests and is shipped with Adaptive Control by default, eliminating the need for sample stiffness estimation.

Please note that options enabled are system dependant and some of them may only be accessible on specific GDS equipment

The Transducer Window

The transducer window can be accessed by clicking on the transducer eye icon in the GDSLab object display or clicking on the digital image of AdvDCS v2 unit and clicking on the “Advanced” button after selecting a transducer.

Please note that each channel on AdvDCS v2 unit has a configurable gain value according to the type of transducer that will be connected. The transducers plug into the GDS AdvDCS v2 unit using Lemo connectors, which are individually colour coded. Pic below shows the transducer sockets on the AdvDCS v2 unit.

Transducer General tab:

The transducer General tab can be used to

1. Apply or remove transducer offset readings,

2. Select the number of decimal places

3. Apply minimum and maximum limits for safety, and

4. Select the real-time graph during dynamic loading.

Transducer Graph:

Shown below the General and Set Target tab, the graph shows a history of the transducer value over time. The three button on the top right of the graph allow to change the graph duration, save the displayed data and clear the graph.

Transducer Set Target tab:

If the transducer can be controlled, this tab allows to set manual targets. Selecting “Hold” will stop the axis associated with the transducer.

Set the targeting rate in the bottom box.

The targeting rate is limited by GDS engineer to a safe value. The targeting rate will automatically revert to a save value if over the limit.

Transducer Calibration tab:

The transducer calibration displays the calibration currently applied to the selected transducer. To change, modify or update the calibration click on “Change/Modify Calibration”. Alternatively, it is possible to modify manually the parameters of the calibration.

The sensitivity value for a new transducer shipped should be calculated from the calibration certificate and entered in the Sensitivity window. Please consult GDS Helpsheet Transducers - Calculating sensitivity and full scale output for calculating the sensitivity of transducers.

Setting the wrong parameters could damage permanently the transducer. Please consult GDS support before adjusting any parameters.

If the panel is greyed-out, this means that the calibration has been locked by GDS. If you need to change the calibration for the selected transducer, please contact GDS support.

If a spare transducer is supplied by GDS with the AdvDCS v2 unit, the calibration values will be already saved in the AdvDCS v2 unit. The calibration values between the two transducers can by changed by clicking on the “Change/Modify Calibration” option and selecting the appropriate calibration file.

From this window it is possible to select an alternative calibration or to modify an existing one. In order to re-calibrate a transducer or calibrate a new transducer, click on the “Calibration Wizard” button. Please refer to the following helpsheet for instructions on how to use the Calibration Wizard: 214 GDS Helpsheet - Change, update or create transducer calibrations in AdvDCS V2-based systems

AdvDCS v2 Device Interface

The Device Overview

The Device Overview can be opened by clicking on the device image in the Object/Hardware Display window.

Channels

The Channels Tab lists all of the transducers connected to a AdvDCS v2 unit, showing their current readings, and allowing the User to apply/remove offsets.

Real Time Graphs can also be enabled here for each channel, by ticking the RT Graph checkbox.

Waveforms

The Waveforms Tab allows the user to select the type of waveform needed for their dynamic cyclic tests. The AdvDCS v2 unit is pre-programmed with a sinusoidal waveform with a Custom waveforms upgrade.

Please refer to 225 GDS Helpsheet - Custom Waveforms in AdvDCS V2 devices for instructions on how to use, add or modify custom waveforms.

Sine wave is the default waveform in AdvDCS v2 unit. To select a custom waveform, click on the Custom Waveform check box, then click on the Waveform Manger tab and select the desired Custom Waveform. AdvDCS v2 gives an option to store up to 8 Custom Waveforms at one time, each composed of maximum 16000 points.

For more information on creating a custom waveform, please refer to Helpsheet 196 – Custom Waveforms for Unity Devices.

Docking

The Docking Tab allows the User to position the machine by pressing the Extend/ Retract button prior to the test. This can be done by moving at a constant rate unlit the Hold button is pressed. When the 'Maintain load after docking' option is enabled, the machine will stop after the target load is reached. This will disable the Extend button until the Set Undocked button is pressed.

To find the travel limit of the machine on both sides of the current position, the machine should be allowed to travel to its maximum and minimum limits without a sample inside the cell. Rebooting the device will set these travel limits to Unknown (as shown in the pic on the right side)

Please note that the Extension/Retraction rate can be modified using the Speed (mm/s) option in the window, however, the machine will not move faster than maximal speed pre-defined by GDS.

Dynamic Stages

This tab gives various options related to dynamic stages.

Real Time Graphs

1. Show Graphs - Generates real time graphs for all transducers which have this option enabled.

2. Graph Length (sec) - The graph length (in seconds) can be changed.

3. Real Time Graphs Position - Saves the window position in case the user wants to restore the size and position of real time graphs when GDSLab reopens.

4. Launch Realtime Graphs - Launches the real time graphs selected.

XY Graphs

Gives option to add / remove XY Graphs launched during the dynamic test.

The duration of graph (in seconds) and sample time (rate at which data is plotted, in ms) can be changed.

Lead in / Lead out

This panel enables setting custom lead in and lead out for dynamic trajectories.

Lead in duration indicates the time it takes the dynamic stage to reach full amplitude after the start of the trajectory. Lead out duration indicates the time before the end of the trajectory when the amplitude starts to reduce.

Magnitude % indicates the percentage of nominal amplitude at the start (lead in) and at the end (lead out) of the trajectory.

The image on the bottom right shows a dynamic stage with 1 mm amplitude where the following settings have been used:

• Lead in duration: 10 seconds

• Lead in magnitude: 20%

• Lead out duration: 5 seconds

• Lead out magnitude: 80%

Enabling custom Lead in / Lead out will override any lead in/out settings specified in GDSLab.

Cycle Data Plan

The Cycle Data Plan tab gives an extra option to select a Cycle plan which allows the user to set a series of "on" "off" data saving when running dynamic tests.

A Cycle Data Plan file (*.cyc) is a Comma Separated Value file where the first column indicate the cycle when to start recording data, and the second column indicates the cycle when to stop. Each line in the file will represent a new cycle interval.

For example, if we wish to start data recording from stage 1 and end at stage 9, we would write the first line as “1”,”9”. If we then want to resume data recording at stage 11 and end at stage 19, we would write the second line as “11”,”19”. The example .cyc file can be downloaded from here:

Log

The System Log saves all of the information about the system such as requested dynamic trajectories, errors and fault messages. The log window is useful for diagnosing issues with the machine. When contacting GSD support for any issues, please provide the messages shown in the log.

Transducer Graph

The Transducer Graph tab shows the real time graphs of the transducers selected from the ‘select channel’ drop down menu. It also gives options to save data to file, save image to file, copy image to clipboard and show histogram and FFT.

Advanced

The advanced tab is used to

1. Load a configuration file provided by GDS engineers

2. Override errors for devices detached from Sigma3 dynamic pressure controllers

3. Manually select an alternative control tuning

Use only if instructed by a GDS Engineer

Setting up the Hardware Components

The hardware set up comprises of an LVDT Signal Conditioning board and a Digital Control System unit (AdvDCS V2). 

The LVDT Signal Conditioning Unit is used to convert signals from the LVDT transducers used on the EMDCSS, from a moderated signal to read as a voltage. Therefore the transducers get plugged straight into this unit and then a connecting DIN-to-LEMO cable is connected to the corresponding channels on the AdvDCS box. 

DCS Box with LVDT conditioning unit

The EMDCSS has two connections to the DCS control box.

• A digital CAN cable with an encased RJ45 connector on the termination connecting to the EMDCSS and a normal RJ45 connected on the termination connecting to the AdvDCS box.

• An analogue 9 pin to 9 pin connector for the axial quadrature signal.

Pictures of cables, connectors and sockets On a) EMDCSS and b) DCS sides

The remaining transducers from the EMDCSS are plugged into their corresponding channels on the AdvDCS unit. The Diagram below represents all the system connections.

Schematic showing EMDCSS Connections

Setting up the Transducer Arrangement

Under normal setup, there are two displacement transducers for the vertical axis and one displacement transducer for the horizontal axis. The vertical axis has a P & G type transducer for long-range coarse control and an LVDT type transducer for its short-range fine control.  These have a range of 125mm and ±2.5mm respectively.

An encoder reading is also available for the vertical axis, but because of the error induced by the deformation of the components on the vertical axis this reading should not be used for test purposes.

The Horizontal axis has a short range LVDT transducer with a range of ±10mm as well as a transducer built into the encoder of the actuator.

Pictures of displacement transducers a) vertical axis long-range transducer b) vertical axis short-range LVDT and c) horizontal axis short-range LVDT

As an optional upgrade a high accuracy shear LVDT is available. This transducer will be attached to the sample pedestal, with a spring-loaded armature resting on the side of the top cap (please refer to the helpsheet ‘Simple Shear Sample Preparation’ attached in the ‘setting up a sample’ section).

The long-range axial displacement transducer is plugged into the yellow channel on the AdvDCS box. The axial and horizontal LVDTs are connected to the matching serial number channels on LVDT conditioning box. Then the DIN-to-LEMO cables are connected to the green and grey channels (channel #5 and channel #6) on the AdvDCS box for the axial and horizontal LVDTs, respectively.

The axial load cell is plugged into the black channel (channel #0) and the primary and secondary shear load cells are plugged into the brown and red channels respectively (channel #1 and channel #2). 

Make everything tidy

Check all cables are neatly arranged.  Plumb any required fittings into the pedestal and topcap.  Put the required pedestal in place. 

Safety Precautions

When working around the EMDCSS unit, be aware that it has moving parts, even though the majority are encased. 

There is an emergency stop button on the front side of the machine, which when pressed stops the machine immediately. A system error message is then displayed in the GDSLab device status tab.

Initial Power Up

The 120/240 Volts A/C, 50/60Hz, connector is plugged into the applicable socket on the side of the EMDCSS.

Before powering up the system, make sure that the emergency stop button is pressed. Power on the computer, then power on the DCS.

Initial Software Set-up and Transducer Check

Run GDSLAB. When GDSLAB first runs, you should select the relevant ini file for the test station from the list of available ini files which will have been provided by GDS in the GDSLab CD or USB stick. Please refer to GDSLAB manual for detailed instructions. After selecting the ini file, a window will pop up showing the connection of DCS box to the PC.

        Pictures showing (a) selecting the ini file and (b) connection of DCS box

Select ‘OK’ to confirm the connection of AdvDCS box and proceed to the ‘Object Display’ – Within the Object Display, you must be very careful to ensure that the following parameters are correctly and accurately set.

• Load cells (axial and shear) range and sensitivity

• Pore pressure range and sensitivity

• Axial displacement range and sensitivity

• Shear displacement range and sensitivity

Please refer to helpsheet 216 ‘ADVDCSv2 Device Interface’ (attached above) for checking the calibration details of transducer.

Once these have been set up you can proceed to perform ‘sanity checks’ on the transducers. Left click on the digital image of DCS box to open the transducer window. Live readings of the transducers can be seen in this window.

Load Cell Check

Displacement Transducer Check

To check the displacement transducer, the safest way to do is to use the motor control as the motors communicate with the acquisition system. To do so, release the emergency stop button which will energize the motors. Since the abort button was pressed earlier, there will be errors in the memory and the transducer readings will appear red in the GDSLab object display. Click on the read button twice in the GDSLab object display to remove errors in the memory and the transducer reading should appear blue. The machine is now ready to be moved.

To perform sanity checks on the axial displacement transducers, in the GDSLAB object display, click on the control parameter tab to target axial displacement (encoder). Set target displacements and see if the top cap platen is moving correctly. Make small movements at first to conform the distance moved is the same as the target value (eg move 2mm and measure with a ruler). Now drop the LVDT armature and set it at the middle marked position with the transducer body (zero reading point, see pic to the left below). Tighten the screw on the armature block (see pic to the right below) to hold the armature in place. Target 2mm axial displacement (encoder) in the GDSLab and check if all the axial displacement transducers move by 2mm.

Pictures showing fixing the axial LVDT at middle marked position

For the horizontal transducer sanity checks, target a small displacement (e.g. 2mm) on the horizontal displacement (encoder) and check that both horizontal transducers move by the same value. Conform the distance moved is the same as the target value (measure with a ruler).

Top Cap and Pedestal Alignment Check

The short range horizontal LVDT should be as close to zero as possible when the top cap and pedestal are exactly in line. This is important so that when the machine is loading the sample, the sample is loaded normal to the axis and not at an oblique angle. 

To do so, put the top cap and pedestal (without the porous discs) in the EMDCSS and tighten the bolts. From the GDSLab object display, use the CP command to bring the top cap down to the maximum positive position using the Axial Encoder option. Also, target zero position on the horizontal LVDT. Check that the top cap and pedestal are now align with each other.

When setting the transducer in place, it is near impossible to get it exactly to 0, therefore a slight offset is applied. A soft zero offset can be applied in the transducer window. This offset will remain fixed unless the user redefines it. It is also important to check this offset every so often to ensure that this offset hasn’t wavered, and redefine it if necessary.

Before shipping the EMDCSS machine to you, the horizontal LVDT is set close to 0 when the top cap and pedestal are aligned. If the offset value is high, then please follow the instructions in the ‘LVDT Transducer Setup’ section to bring the offset close to 0.

Picture showing top cap and pedestal aligned with each other at zero horizontal LVDT position

In addition to this, the vertical short range displacement transducer needs to be set up correctly, in terms of specimen height etc.  For example, when using a specimen height of 20mm, when the sampled is docked the transducer needs to be near the top of its range.  The vertical LVDT transducer has a range of +/- 2.5 mm, therefore the transducer should read approximately -1.5.  This is in order for the transducer to be able to read the full displacement of the sample, without going over its reading threshold. 

Checking Machine Functionality

The EMDCSS machine should stop automatically when it reaches the upper or lower limit. This can be checked by targeting values beyond the upper travel limit (eg -60mm). A warning will be displayed on the Object Display status bar when this occurs.  If the machine does not stop automatically or makes any loud noises when reaching the limits, push the Emergency Stop button immediately and contact GDS for further instructions.  Carry out the same procedure for the bottom limit switch (+60mm). Then repeat the same procedure for the shear limit switches.

Double check the load-cell calibration. If you have a (small) proving ring or known working load cell, put that between the topcap and pedestal, and compare its reading with the reading shown in GDSLab for the system load cells. If you do not have such a convenient load measuring system then adopt some ad hoc means. For example, you could use the "rubber bung" dummy test specimen described below. You know roughly your own weight. Press your whole weight down onto the dummy test specimen and observe the deformation or ask a colleague to observe it for you.  You will now have a rough but very convenient indicator of load. 

Machine functionality checks also involve running a few tests (explained below) on a dummy sample. Please refer to the GDSLab handbook for a step by step guide on setting up a test stage (Chapter 3) and selecting the relevant test modules (Chapter 6) for carrying out the tests.

Running the First Test

Install a dummy test specimen.  This could be a rubber sample for instance.  Place the rubber sample in the cell.  Perform a constant rate of strain and constant rate of shear test (using the Advanced Shear test module).  Choose parameters appropriate to the dummy test specimen. Use a strain rate of 50mm per hour and termination conditions of 2mm for each axis.  Plot the results and check for noise levels.  On the screen, plot load cell against displacement for each axis.  From the plot, calculate the stiffness of the dummy test specimen in kN/mm.  Please refer to the article below for the importance of stiffness estimate in dynamic load controlled tests.

Running the First Dynamic Test

Select the Dynamic Shear module and choose axial displacement control. Select 0.1Hz at +/- 0.2mm axially as well as in the shear plane (if the dummy test specimen will stand it).  Choose 100 data points per cycle, 5 cycles on, 0 cycles off, terminate after 5 cycles.

Running Other Tests

Going back to the GDSLAB object display, you can check that the load control is working by setting a small change in target load. Observe the deformation of the dummy test specimen. From your ad-hoc calibration of the stiffness of the dummy test specimen, check that the observed deformations are about right.On the screen, note the resolution (i.e. variation) of control of axial force (load).  Normally, you should expect better than 1% of full range at loads greater than approximately 1/20th of full range.

If all is OK you can then start testing with real soil.

User Adjustments

So long as the system hardware remains unchanged there will be no user adjustments required on a day to day basis. If transducers are changed it is very important to update the calibration details for the data acquisition system. The main user software adjustment between test is the selection of stiffness estimate of the test specimen (explained above).

Setting Up a Sample

HARDWARE

EMDCSS, VDDCSS, MDDCSS, GDSSSS & ADVDCSSv5

Sample preparation

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This helpsheet is designed to help you prepare your sample.

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Option 1 - Using support brackets

Items Required:

• Base pedestal with porous disk

• Top cap with porous disk

• Membrane

• Both lower lock rings & screws

• O-rings

• Teflon coated sample rings

• 2 off pedestal support brackets

• Soil sample

Place the sample membrane over the pedestal and then place and screw down the lower lock ring.

Place the o-ring on the pedestal (left side photo) then place and screw down the upper lock ring to engage the o-ring (middle photo). Place the sample rings allowing 3 rings above the desired sample height (right side photo).

Wrap the membrane down over the sample rings. Fit the support brackets. Place, compact and level the soil sample.

Place the top cap on the sample. Tighten the support bolts against the top cap and then slide membrane around the top cap. Roll the o-ring down over the membrane.

• Place the prepared sample into the EMDCSS.

• Extend using vertical displacement control parameter so that the loadcell is within a few mm of the top cap.

• Target ≈0.01kN axial load in the object display.

• As the loadcell contacts the top cap, make sure it’s aligned correctly, gently correct it by hand if required.

• When they are correctly aligned and docked, set the EMDCSS to hold displacement and screw the top cap into the loadcell above.

• Then zero both axial displacement transducers.

Losen and remove the top cap support brackets. Finally, screw in the draining tubes if required.

Option 2 - Using vacuum former

• Base pedestal with porous disk

• Top cap with porous disk

• Membrane

• Both lower lock rings for vacuum former

  • 3 spigot holes each

  • screws

• O-rings for vacuum former

  • 99.5x3mm silicone ring

  • 94.5x3mm nitrile ring

• Teflon coated sample rings

• Vacuum split former

• Spigots

• Soil sample

• Place the sample membrane over the pedestal

• Put the lower o-ring followed by the lower lock ring

• Screw them in place.

Place a second o-ring on the pedestal then place and screw down the upper lock ring to engage the o-ring. Place on the sample rings allowing 3 rings above the desired sample height.

Place the silicon (orange) ring along the bottom groove of the vacuum former, as shown in the picture above. Insert the 4 bolts that will hold the pedestal to the EMDCSS platen. These need to be in place at this stage as they will be covered by the split former (blocking access to the bolt holes) when the assembly is placed in the EMDCSS. Place the pedestal on a small block or other spacers so that is stands raised and with the bolt heads flush with the base of the pedestal. The pictures below show this being done by placing the pedestal on top of the top cap.

Place the two-part split ring of the vacuum former around the sample rings, with the bottom cut-outs positioned in line with the pedestal bolt sockets. The three spigot holes on the vacuum former also need to be aligned with the slots on the middle ring sample ring. Push down until the silicon ring seal slips in place against the middle sample ring.
Insert the 3 spigots in the spigot holes visible on top of the vacuum former. These will ensure the alignment of the sample rings. Next finger tighten the bolts on the side of the sample former to push the spigots against the sample rings.

Use only enough torque to prevent the spigots from moving. Overtightening these bolts may damage the sample rings.

Fold back the top of the membrane over the vacuum former and then use an o-ring to hold the membrane in place.
The membrane wall should be as flush as possible with the inner perimeter of the sample rings. Pull through slack where possible. If the membrane and o-ring start to slide up off the former folding the membrane back upwards and adding a second o-ring will prevent this.

Connect a vacuum line or pipette ball to the drainage pipe on the side of the vacuum former using a rubber hose and
apply vacuum. The membrane will then be pulled flush against the inside of the sample rings. When the sample is in place the vacuum former will later be moved to the pedestal stand on the EMDCSS under vacuum. This should be taken into account when setting up the vacuum pump, ensuring the hose has enough length or the pump has enough mobility to allow that.

Form the specimen inside the mould using the selected preparation method.

If tamping is used to achieve the target density then special care should be taken not to puncture the membrane when tamping along the edges.

Attach the top cap to the EMDCSS ensuring the porous disc and all four upper bolts to the loadcell are tightened in place. Place an o-ring on the top cap and roll it up until it is close to the top edge.

Using GDSLAB’s Object Display raise the axial actuator (negative direction) until there is enough clearance to install the specimen and pedestal set.

Keeping the vacuum former under vacuum move the pedestal to its stand on the EMDCSS and bolt it securely in place.

Use GDSLAB’s Object Display to move the actuator down until it is 2 to 5mm away from the top of the specimen.

Measure the gap (if any exists) between the top of the sample and the top of the membrane. Then measure the thickness of the porous disc on the top cap.

Set the horizontal and vertical load cells to zero then target a small vertical seating load (suggested between
0.001kN and 0.005kN). This will make the vertical actuator move down. Carefully observe the top cap’s approach to the specimen and cancel its movement if it seems out of alignment.

If it’s out of alignment, make the necessary adjustments by moving the horizontal actuator in small increments until the specimen is perfectly aligned with the top cap, then set the same vertical sitting load target.

Note! If very low load targets are used, the friction on the vertical axis might make the system read the target vertical load target before the top cap reaches the specimen. If this happens, hold moving on the vertical axis by clicking hold in the Control Parameter window for vertical load, set vertical load to zero and re-target the sitting load.

When the target sitting load is reached the top cap should be completely docked (in contact) with the specimen.
Measure the height of the portion of the porous disc still visible and calculate the difference from its total thickness.
The difference should be equal or very similar to the gap between the top of the sample and the top of the membrane. If it is not, check if the specimen if correctly aligned with the top cap.

If any further correction is necessary to retract the top cap before moving the horizontal axis and then repeat the docking procedure.

If the alignment seems correct and the sitting load target has been reached but the top cap is not docked, then set the vertical load to zero and re-apply the same sitting load target.

Once docking is complete, turn off the vacuum pump and disconnect the hose from the side drain on the former. Pull down the o-ring holding the membrane and place it around the base of the pedestal, so it does not obstruct the disassembly of the split former. Slide the member up around the top cap.

Roll the o-ring on the top cap down over the membrane and then fold the membrane over the o-ring.

Next, loosen the 3 spigot bolts and then undo the bolts holding the two halves of the split former together. Remove the split former together with the spigots carefully to avoid deformation to the specimen.

The nitrile o-ring, previously placed around the base of the pedestal, can now be rolled up and placed around the lower sample ring, together with the silicone ring. This will be their position during the test. Connect drainage pipes as required.

Installation of top cap LVDT

Items required:

• LVDT

• LVDT clamp bracket

• LVDT clamp insert (fitted inside the LVDT clamp bracket)

• LVDT mounting plate

• Screws

Insert the LVDT in the LVDT clamp insert, then insert the screws in the LVDT clamp bracket and mounting plate to connect these two parts together. Attach the assembly to the base pedestal and tighten the screws.

The LVDT transducer has 3 marking points. The LVDT transducer is linear in the range, symmetrically around a zero voltage point. This is shown by the middle marking point on the LVDT armature. The two outer markings shows the range of motion over which the data recorded is linear.

Adjust the position of LVDT such that when it is in contact with the top cap, the armature is on the middle marked position. This way the LVDT will be able to record the data on both sides of the zero voltage point. Tighten the upper screw on the clamp bracket with an allen key such that the LVDT is fixed firmly but be careful not to over tighten it.

• Page:
  016 GDS Helpsheet - GDSLab System Requirements (GDS Instruments Knowledge Base)

  • helpsheet
  • software
  • gdslsab
  • requirements
• Page:
  047 GDS Helpsheet - Using the Extension Top Caps (GDS Instruments Knowledge Base)

  • triaxial
  • tas
  • extension
  • passive
  • top_cap
  • helpsheet
• Page:
  078 GDS Helpsheet - Fitting Swagelock Connectors (GDS Instruments Knowledge Base)

  • helpsheet
  • swagelock
  • fittings
  • nut_and_ferrule
• Page:
  145 GDS Helpsheet - EL, STD & ADV Controllers o-ring sizes and replacement (GDS Instruments Knowledge Base)

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  146 GDS Helpsheet - DSS - Simple Shear Sample Preparation (GDS Instruments Knowledge Base)

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  195 GDS Helpsheet - GDS Unity Interface (GDS Instruments Knowledge Base)

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  196 GDS Helpsheet - Custom Waveforms for Unity devices (GDS Instruments Knowledge Base)

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  212 GDS Helpsheet - Saturate Midplane Pressure Transducers with Saturation Chamber (GDS Instruments Knowledge Base)

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  213 GDS Helpsheet - Direct Shear Setup for Shearbase and EMDCSS (GDS Instruments Knowledge Base)

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  214 GDS Helpsheet - Change, update or create transducer calibrations in AdvDCS V2-based systems (GDS Instruments Knowledge Base)

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  215 GDS Helpsheet - Installation of Dynamic Drivers (GDS Instruments Knowledge Base)

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  216 GDS Helpsheet - AdvDCS v2 User Interface (GDS Instruments Knowledge Base)

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  217 GDS Helpsheet - Replacing a DYNTTS power supply and Opto-Isolator board (AB Drive Type) (GDS Instruments Knowledge Base)

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  218 GDS Helpsheet - TraditionalCell Loadframe Control Parameter Tool - Instructions (GDS Instruments Knowledge Base)

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  219 GDS Helpsheet - GDSLab calibration wizard (GDS Instruments Knowledge Base)

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Test Procedure

The typical testing procedure to be carried out on an EMDCSS is consolidation stage, followed by a period of dynamic shearing and then a monoclinal shearing, to failure.  This will essentially give the user the required data.

Please refer to helpsheet 216 ‘ADVDCSv2 User Interface’ for selecting the waveform shape for dynamic cyclic test, and to enable the realtime graphs for transducers to be displayed during the test. Refer to the GDSLab handbook for setting up the test parameters and the test stages.

LVDT Transducer Setup

It may be necessary at some point during the life of the EMDCSS device to realign both the horizontal and vertical short range transducers. 

Although they are quite difficult to access it should be possible to adjust the position without removing the EMDCSS front cover. If you find it too difficult to access, the lower front cover can be removed. Align the topcap and pedestal using the Object Display. This is best achieved by getting them as closely lined up as possible, then with the flat edge of a metal ruler progressively use small increments to align them perfectly.

As shown in the figure below, the horizontal LVDT transducer wire is fed through a hole in the base of the device and the LVDT body clamped in place.  As mentioned previously, it is vital that when the topcap and pedestal are exactly in line, the reading of the transducer is as close to 0 mm as possible.  This is so that any displacement fore or back of the pedestal can be measured accurately.  This horizontal transducer has a range of +/- 10 mm.  When aligning it there is bound to be a slight reading either side of zero which can be set as a zero offset.

Photo showing placement of horizontal displacement LVDT

When locking the LVDT into place, also ensure that the black lead is pushed as far down, toward the base of the device, as possible to avoid interaction with the plate that sits over the top of it.

As with the horizontal LVDT, the vertical LVDT is threaded through a hole in the lower side of the device and up to the bracket (shown in the picture below). The stainless steel armature has a magnet, clearly distinguishable, in one end of the armature.  This end needs to be fed through the LDVT and be in position through the LVDT bracket.  The other end of the armature is placed within the stainless steel block on the base of the device.  It is important to leave some lee-way for future adjustment - therefore the user should only position the armature a portion of the way into the block before tightening it in place.

Photo showing alignment of vertical LVDT

The armature should also be as straight as possible. The bracket holding the LDVT in place can be re-positioned by undoing the bracket screws attached to the device and manoeuvring the bracket so that the LVDT and rod line up perfectly.

The metal plate positioned below the bracket holding the LVDT in place is a resting plate for the armature when working with the sample (see picture below). By pulling the armature up and sliding the metal plate across, there is an indentation on the plate that the armature can rest in.  This is necessary for two reasons; for ease of access to the sample, as well as not to bend the armature while taking the pedestal/topcap in and out.

Photo showing metal plate to rest rod on while preparing the sample

User Maintenance

The EMDCSS requires only occasional user maintenance and should perform for many years, assuming it is cared of correctly during the use.  Care must be taken especially during sample preparation, insertion and removal not to drop particulate matter onto the linear guides or to allow water to drain onto the linear guides.

 It is recommended that the user undertakes a check for friction annually and applies a small amount of oil to the linear guides if required at the same time.  There should be no other user maintenance required.

Annual Test for Friction

The following tests check that the level of friction from the linear guides in the EMDCSS is within the expected range.  These should be carried out with no sample present so the axial loadcell and horizontal loadcell 2 can measure only the friction in the system.

To check for static friction on both axes use the object display to set position to 0mm, 2mm, 0mm, -2mm, 0mm, 2mm, 0mm.  Do this for both vertical and shear axis.  Note the relevant loadcell (axial loadcell or shear loadcell 2) reading at each position.  The friction value is: 

                   (max load – min load)/2

• Static axial friction should be <±0.025kN worst case ≤±0.03kN

• Static shear friction should be <±0.025kN worst case ≤±0.03kN

To check dynamic friction setup an advanced shearbox stage to ramp from 0mm to +10mm in 1 minute, logging every 3 seconds. Then setup a second ramp coming back to 0mm in 1 minute, again logging every 3 seconds.  Dynamic friction is (max load– min load)/2 where max load is max load observed during positive ramp and min load is minimum load observed during negative ramp.

• Dynamic axial friction should be <±0.025kN worst case ≤±0.03kN

• Dynamic shear friction should be <±0.025kN worst case ≤±0.03kN

 If you have difficulty performing these tests of are concerned your EMDCSS does not pass the tests please contact GDS technical support by sending an email including your results files to support@gdsinstruments.com.

Annual Lubrication

A small amount of lubrication may be required to maintain the linear guides of the EMDCSS.  Please note that excess lubrication will likely not reduce the friction in the machine, but may instead lead to dust/particle accumulation and thus additional friction in the guides.

Note: a water dispersing oil such as WD40 is NOT suitable for lubricating this machine.  A good quality machine grease such as Castrol EP2 is recommended.

If following the friction checks the apparent friction on the axis is less than ±0.01kN you should not have to apply any lubrication.  If the friction exceeds ±0.01kN continue as described below.

To lubricate the horizontal guides set the EMDCSS to its reverse horizontal travel limit.  This can be easily done using the object display and targeting beyond the travel range, eg horizontal displacement =-20mm.  Next place a small drop of grease onto each of the exposed guides as far back into the machine as possible (reaching underneath the back rubber skirt at the front of the base platen).  A small syringe is ideal for this.  Lastly cycle the machine between the forward and rear travel limits 5 times to distribute the grease across the guides.

The vertical guides are more difficult to reach but can be exposed by setting the machine to its upper travel limit.  They can then be accessed behind the topcap position.  Again, place a small drop of grease onto the bearing as high up as possible, then cycle the vertical axis between upper and lower travel limits 5 times to distribute the grease.

Note: Take care when inserting hands/fingers into the EMDCSS.  It is recommended to push the STOP button whenever there is a risk of trapping hands/fingers being trapped in the machine.