Rock Testing

The list below shows the different tests, gives an explanation of each test and links it to apparatus that can perform these tests. All tests can be managed and recorded through GDS’s software GDSLAB and this guide is designed to help you find the right equipment for your purpose. Rock testing measures is usually performed at high load on intact samples, sometimes at high temperature. There are a host of different tests you can run on rock from a variety of testing apparatus.
Axial or Radial Deformation

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.

Consolidation Testing

Triaxial consolidation refers to the application of a constant cell and back pressure to the sample whilst monitoring the volume change within the sample.


One dimensional consolidation refers to the application of a load to the top of a sample contained within a fixed ring.

Constant Pressure Source

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).

Constant rate of Loading (CRL) Consolidation

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.

Constant rate of strain (CRS) Consolidation

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.

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.

Cyclic Testing, Slow
Damping Ratio in Torsion

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 following products can perform this test:-
Resonant Column Apparatus (Stokoe Type)
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.

Gas Adsorption onto a sample

Gas adsorption is the process of gasses coming into contact with a solid, and part of the gas being taken up by the solid, i.e. being adsorbed (note, different to absorb).

The GDS Adsorption cell is a Twin Cell based system used for the Adsorption of a Gas onto a chosen sample. One chamber will have a gas with a known volume and pressure. The second chamber will hold a sample with known volume under a vacuum. The gas is then introduced to the sample chamber and the process of adsorption begins.

The following products can perform this test:-
CO2 Gas Adsorption Cell
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.

Resilient Modulus tests

A material’s resilient modulus is actually an estimate of its modulus of elasticity (E). While the modulus of elasticity is stress divided by strain for a slowly applied load, resilient modulus is stress divided by strain for rapidly applied loads – like those experienced by pavements.

Resilient modulus is determined using the triaxial test. The test applies a repeated axial cyclic stress of fixed magnitude, load duration and cycle duration to a cylindrical test specimen. While the specimen is subjected to this dynamic cyclic stress, it is also subjected to a static confining stress provided by a triaxial pressure chamber. It is essentially a cyclic version of a triaxial compression test; the cyclic load application is thought to more accurately simulate actual traffic loading. Please note: Some apparatus may require additional components or software modules to perform certain tests.

Stress Paths

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.

User defined waveforms

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.


All GDS advanced dynamic systems allow user defined waveforms to be used, with the enterprise level dynamic systems having user defined waveforms as an optional feature.