Soil Testing

Allows all controllable parameters within a HCA to be targeted by the user for a test stage.

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.

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

Axial deformation is measured by a displacement transducer in all GDS systems (LVDT, LDT or digital gauge).  Radial deformation is calculated as standard by measuring the volume change to 1mm3 directly on the back pressure controller.  For direct measurements of radial strain (i.e. transducers mounted upon the sample, and direct measurements of axial strain in the same way, GDS can supply a Hall Effect local strain set or an LVDT local strain set. Please note: Some apparatus may require additional components or software modules to perform certain tests.

The B-Check is a pre-test to check that the specimen is sufficiently saturated by measuring the Skempton pore water pressure parameter B. The cell pressure is increased to the specified value whilst the back pressure remains on hold volume (i.e. the undrained state). The system compares the change in pore pressure (Δu) caused by the increase in cell pressure (Δσ3). The value of B is calculated as Δu/Δσ3.  If your GDS triaxial testing system has a cell pressure controller and a pore pressure transducer, then the B-check is automated within the GDSLAB software. Please note: Some apparatus may require additional components or software modules to perform certain 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. 

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.

A Consolidated Drained triaxial test (CD test) is a constant rate of strain shearing test performed with back pressure control on the sample (i.e. the back pressure valve is open).  The test must be performed sufficiently slow such that the sample can drain and therefore no excess pore pressures should build up.  For this reason a CD test is usually performed particularly slowly, particularly on samples of low permeability.  The sample has first been saturated and consolidated. Please note: Some apparatus may require additional components or software modules to perform certain tests.

A Consolidated Undrained triaxial test (CU test) is a constant rate of strain shearing test performed undrained, i.e. with no back pressure control on the sample (i.e. the back pressure valve is closed).  Unlike a CD tests (Consolidated Drained), excess pore pressure will be seen to build up.  The sample has first been saturated and consolidated. Please note: Some apparatus may require additional components or software modules to perform certain tests.

Consolidation simply applies a constant cell and back pressure to the sample whilst monitoring the volume change within the sample. Please note: Some apparatus may require additional components or software modules to perform certain tests.

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.

All GDS controllers are designed for use as constant pressure sources.  The stepper motor constantly adjusts itself to ensure the desired pressure is maintained, with the additional advantage that volume change is measured to 1 cubic mm* (*except the pneumatic controller which only regulates pressure and has no capability for measuring volume change or flow).

The constant rate of flow test simply maintains a constant base pressure whilst applying a constant flow through the top of the specimen. A maximum hydraulic gradient can be set which will pause the rate of flow if the pressure differential between the top and the base of the sample gets too large.  Please note: Some apparatus may require additional components or software modules to perform certain tests.

Provides a controlled ramp of load while the back pressure is maintained. There is also the option to limit the rate of strain if a specified hydraulic gradient across the sample is exceeded.

Provides a controlled ramp of strain while the back pressure is maintained. There is also the option to limit the rate of strain if a specified hydraulic gradient across the sample is exceeded.

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.

Controlled hydraulic gradient means the user can set a maximum pressure gradient across the sample.  In triaxial permeability testing this coule be the difference (i.e. the gradient) between the applied back pressure at the top of the sample and the measured pore pressure at the base of the sample, or in triaxial shearing it could be related to the excess pore pressure generated during a shearing test. If the user defined value is exceeded then the test will be paused until the sample equilibrates enough to bring the difference back to within the stated pressure before continuing.  Effectively by having control on the hydraulic gradient the test will not run too fast for the permeability of the soil. 

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.

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.

The damping ratio is a measure of describing how oscillations in a system die down after a disturbance i.e. how the shear waves generated in the sample die down after a test is complete. This test can be carried out in torsion or flexure through the resonant column.

The damping ratio is a measure of describing how oscillations in a system die down after a disturbance i.e. how the shear waves generated in the sample die down after a test is complete. This test can be carried out in torsion or flexure through the resonant column.

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.

Allows load and displacement, in the axial and rotational directions, to be applied to a HCA specimen at dynamic rates. 

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

Enables application of load to a specimen for approximately less than ten seconds, and at frequencies greater than 0.1 Hz during cyclic loading.

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.

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.

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.

Determination of the shear wave velocity within a soil mass without physically probing the soil with instruments. Please note: Some apparatus may require additional components or software modules to perform certain tests.

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.

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 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.

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.

Is the deformation of an object through bending, curving, or flexing.  This non-standard can be performed in the GDS resonant column apparatus as it has the ability in the software to reverse the polarity in one of the coils and switch 2 of the other coils to be open circuit, thus resonating the soil sample in flexure (bending).

The standard test performed in a resonant column cell is resonance in torsion.  By establishing the resonant frequency in torsion of a soil sample, the soil shear modulus can be calculated.

Determination of the variation in maximum shear modulus of a soil mass with respect to depth from the ground surface.

The damping ratio is a measure of describing how oscillations in a system die down after a disturbance i.e. how the shear waves generated in the sample die down after a test is complete. This test can be carried out in torsion or flexure through the resonant column. Please note: Some apparatus may require additional components or software modules to perform certain tests.

Enables a cyclic axial stress to be applied to the test specimen under a constant confining pressure for a specified number of load cycles before the resilient modulus or permanent deformation tests are started. This conditioning phase helps to minimise the effects of imperfect contact between the system platens and test specimen, as well as eliminate effects due to the time interval between specimen compaction and loading.

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

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 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.

In a triaxial test, a stress path is described by any change in stress state in any direction on a sample.  To be able to perform a stress path test it is generally considered that control of both the axial stress and the radial stress is required.  With this level of control, linear paths may be controlled of either axial stress and radial stress, p and q (deviator stress), or s and t paths. Please note: Some apparatus may require additional components or software modules to perform certain tests.

An Unconsolidated Undrained triaxial test (UU test) is a constant rate of strain shearing test performed without back pressure control on the sample (i.e. the back pressure valve is closed).  The test is generally quite fast as drainage is not required from the sample.  There is no requirement for the sample to be saturated or consolidated before the shearing stage. Please note: Some apparatus may require additional components or software modules to perform certain tests.

Dynamic cyclic triaxial testing is usually performed with a cyclic loading pattern which is the shape of a sine wave.  Some experiments require a unique waveshape to be applied to the soil, for example in recreating earthquake loading from a measured seismograph trace.

Enables load or displacement to be applied to a simple shear specimen in two horizontal shear directions.