Hydraulic Load Frames for Soil

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.

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.

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.

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.

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 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.

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.

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.

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.

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.