Back Pressured Shear Box

Product Code : GDSBPS

The Back Pressure Shearbox (BPS) has the ability to perform direct shear tests with precise back pressure control, for the recreation and measurement of realistic slope failures.

 The BPS range includes a saturated version (control of pore water pressure), an unsaturated version (control of both pore water and pore air pressure) and a dynamic version.

Further Information:

Discover more shear testing equipment for soil testing.

Key features Benefits to the user
Internal loadcell: Internal loadcell for shear and optionally normal force for load measurements as close to the sample as possible for greater accuracy.
Rigid aluminium cell body: To reduce system compliance.
Unsaturated GDSBPS: The unsaturated GDSBPS is based on a standard, saturated device but modified to allow the measurement and control of matric suction (the difference between the pore air and water pressures).
Real-world situations to be modelled in the laboratory: All versions allow the pore pressures within the sample to be controlled. The control of pore pressure during direct shear testing allows real-world situations to be modelled in the laboratory.
Dimensions

L= 930mm x W = 420mm x H=1230mm

Displacement Accuracy

<0.1% FSO

Displacement Range

axial = +/- 15mm, shear = +/- 25mm

Load Range (kN)

25 normal and shear force

Power

240V or 110V 50/60Hz single phase

Pressure Range (MPa)

2

Resolution of Measurement and Control

16 bit (± 25mm = ± 0.7μm(shear), ±10mm = ±0.3μm (axial)

Sample Sizes

60mm (Circular). 75x75 or 100x100mm (Square).

  • The GDSBPS apparatus can be specified with many different options, some are listed below but many more are available. Please contact GDS if the required specification is not listed here or if higher pressures / forces are required.
  • Upgrade to unsaturated back pressured shear box.
  • Maximum back pressure:
    • 1MPa basic.
    • Options to 10MPa.
  • Maximum axial and shear load:
    • 5kN basic.
    • Options to 100kN as part of standard range.
  • Normal (axial) load upgrade to electro-mechanical actuator.
  • Bender elements.

 

Tests supported by the Back Pressured Shear Box, shear testing equipment for soil testing :-

Axial Compression

An axial compression test determines the behaviour of geo-materials when the major load is applied in the axial direction. The specimen load and displacement is recorded while the specimen is compressed. Please note: Some apparatus may require additional components or software modules to perform certain tests.

Back Pressure Cyclic Direct Shear Displacement Tests

Enables a direct shear test in which the load is cycled back and forth to be performed on a specimen at dynamic rates with back pressure applied. 

Back Pressure Cyclic Direct Shear Load Tests

Enables a direct shear test in which the load is cycled back and forth to be performed on a specimen at static rates with back pressure applied.

Back Pressure Cyclic Direct Shear Tests

Enables a direct shear test to be performed on a specimen at static rates with back pressure applied.

Constant Normal Stiffness

A constant normal stiffness condition may be specified and maintained when testing specimens within GDS direct shear and direct simple shear apparatuses. This condition allows for both the normal stress and normal strain to vary as a specimen is sheared based on the contractive and dilative tendencies of the geo-material – here dilation results in increased normal stress and specimen height, while contraction results in decreased normal stress and specimen height. The magnitude of normal stress and normal strain variation is proportional to the constant normal stiffness value specified by the user, entered in units of kN/mm or kPa/mm. Practical applications of such a test condition include modelling the interface between piles socketed or grouted into a geo-material.

Continuous Infinite Volume Flow (either target or ramp)

Some geotechnical applications require the continuous flow of fluid, either under pressure control or via a rate of fluid flow.  GDS manufacture an Infinite Volume Controller (IVC). By connecting 2 GDS pressure/volume controllers in parallel, the IVC system automatically switches between them when they run out of volume thus providing a seamless supply of pressure with unlimited volume capacity.  The IVC can be used with any 2 pressure controllers from the GDS range, i.e. advanced, standard or enterprise. Please note: Some apparatus may require additional components or software modules to perform certain tests.

Cyclic Testing, Slow

Slow cyclic testing may be performed on all GDS triaxial testing apparatus with the appropriate software modules.  The speed the cycles can be applied is determined by the performance of the system.  A standard load frame generally only used for quasi-static testing can perform cyclic testing with periods of around 5 minutes when coupled with GDSLAB control and data acquisition software. Please note: Some apparatus may require additional components or software modules to perform certain tests.

Cyclic loading of samples under either load or strain

Cyclic loading refers to the repeated loading of a sample.  All GDS systems can imply this loading either under load control, or under strain (displacement) control.  Load control will be via feedback from the load cell and displacement control will be via the feedback from the displacement transducer.  Load and displacement control can be performed by all GDS system.  The speed of the cyclic loading depends on the frequency performance (i.e. the dynamic performance) of the system in question.  Dynamic stress control is possible, but only available on the most advanced GDS dynamic because of the additional processing required to calculate the sample area during the cycles.  Please note: Some apparatus may require additional components or software modules to perform certain tests.

Direct Shear Tests

Direct shear tests: The sample is contained inside a rigid box with a horizontal split line at the mid-height of the sample. The shear force is applied to the sample by moving the two halves of the box horizontally relative to each other. The intension is to induce a shear plane to form between the two halves of the sample. Properties can be obtained for the material prior to shear and post failure or residual. Please note: Some apparatus may require additional components or software modules to perform certain tests.

Geo-membrane Shear Test

Direct shear testing of a geo-synthetic material embedded in a soil specimen to determine the shear strength of the geo-synthetic-soil system. 

K0 (K-Zero)

Kzero conditions (or specifically the coefficient of earth pressure at rest) in the context of laboratory testing are where a sample is required to be loaded whilst keeping the area of the sample a constant.  Kzero conditions are maintained in a n oedometer by design due to the radial constraint, however in an oedometer the radial stress cannot be measured therefore the K-zero condition is not measureable.  A Kzero test in a triaxial cell allows Kzero conditions to be applied and measured. The Kzero module allows you to run two tests. 

  • Test 1: Kzero using ramp RADIAL STRESS with direct radial transducer measurement: Uses a direct reading of the specimen diameter to enable the test control to maintain zero diameter change.
  • Test 2: Kzero using ramp RADIAL STRESS with back volume change measurement: Uses the change in volume of the specimen to calculate a theoretical new specimen height thus ensuring the diameter change remains zero.

Please note: Some apparatus may require additional components or software modules to perform certain tests.

Load Control (Static)

Enables application of load to a specimen for tens of seconds or more, and at frequencies less than 0.1 Hz during cyclic loading. Please note: Some apparatus may require additional components or software modules to perform certain tests.

Maximum Shear modulus

Determination of the maximum (i.e., very small strain) shear modulus of a specimen. Please note: Some apparatus may require additional components or software modules to perform certain tests.

Multi-stage Testing

The procedure for conventional triaxial tests requires three separate soil specimens to be sheared to failure under different confining pressures so that Mohr-Coulomb failure envelope can be determined and soil shear strength parameters can be obtained. An alternative procedure is the multi-stage triaxial compression test, which requires only one soil specimen to be tested at three stages of shearing with different confining pressures.


There main advantages of multi stage soil testing is the requirement for fewer soil specimens, as well as reduced testing time.  The advantage of performing the test with 3 separate samples is that if one of the samples is unsatisfactory (perhaps due to sample disturbance for example) then it is likely to be noticed when the Mohr circles are plotted, whereas this could remain unnoticed in the multi stage test. Please note: Some apparatus may require additional components or software modules to perform certain tests.

Oedometer / Consolidation

Uses a datalogger to take settlement readings from a hanging weight oedometer system.  Alternatively, GDS produces an automated oedometer which completely automates one dimensional consolidation testing.

Pore Water Volume Change

Soil testing involves the application of pressure (stress) and the resulting measurement of strain either by measuring displacements or volume change. GDS pressure/volume controllers can apply pressure and measure volume change, or alternatively can apply volume change and measure the resulting pressure. Essential for soil testing.  Please note: Some apparatus may require additional components or software modules to perform certain tests.

Quasi-Static (low speed/creep) Tests

Quasi-static refers to slow speed tests.  Creep tests require accurate displacements to be measurable whilst a continuous, sometimes long term loading is accurately applied. Please note: Some apparatus may require additional components or software modules to perform certain tests.

RAMP and CYCLE pressure or volume change (Saturation Ramp)

Saturation ramp allows you to independently increase or decrease the Cell Pressure and the Back Pressure. The saturation ramp is used to steadily change the pressures in the system either keeping a constant effective stress or change to a desired effective stress.

Static Displacement

A static displacement test involves applying and maintaining a constant displacement to the specimen. The load response can subsequently be observed. Alternatively this may refer to cases where a displacement, which may vary, is applied to a specimen for tens of seconds or more. Please note: Some apparatus may require additional components or software modules to perform certain tests

Static Load

A static load test involves applying and maintaining a constant load on the specimen. The displacement response can subsequently be observed. Alternatively this may refer to cases where a load, which may vary, is applied to a specimen for tens of seconds or more. Please note: Some apparatus may require additional components or software modules to perform certain tests.

Stepped Loading

Stepped Loading provides a means to increase the specimen axial load, whilst maintaining a constant back pressure and measuring the back (pore) volume change. Please note: Some apparatus may require additional components or software modules to perform certain tests.

Standards for the Back Pressured Shear Box, shear testing equipment for soil testing :-