Environmental Triaxial Testing System

Product Code : ETTS

The Environmental Triaxial Testing System (ETTS) is a temperature controlled testing system for stress path testing. Key features include, Frozen Soil Testing, Gas Hydrate Testing, High Pressure Testing and High & Low Temperature Testing

The -200C cooling system provides ideal conditions for frozen soil testing. Its high pressure testing capability (up to 10MPa) along with low temperature provides the ideal environment for Gas Hydrate Testing. The system also has the option for a Heating only system.

Discover more static triaxial testing equipment for soil testing.

Key features Benefits to the user
Heating & Cooling Options: 
-20oC  to +65oC

The cooling system uses a coiled tube section inside the cell, this is connected through the standard ports within the cell base to a glycol cooling unit allowing temperature transfer close to the specimen.
Optional Heating Only System:
Ambient to 60oC
Ambient to 100oC
The heating system works using thermal pads attached to the outside of the triaxial cell then enclosed within an environmental chamber to retain the heat. There are up to 4 temperature sensors relaying back to the control box for enhanced temperature accuracy.
High Pressure (Up to 10MPa):
High Pressure combined with low temperature make it ideal for Gas Hydrate testing.
Gas Hydrate Testing (Gaseous back pressures):
The ETTS can be adapted for gaseous back pressures such as Air, Carbon Dioxide,  Nitrogen or Methane for Gas Hydrate testing.
Frozen Soil Testing:
Cooling to -20oC provide ideal conditions for frozen soil testing.
Load Range (kN)

100

Pressure Range (MPa)

10

Sample Sizes

38, 50, 55mm max diameter

  • LVDT strain set, 
  • Cell top lifting frame, 
  • High pressure Bishop & Wesley (without heating & cooling).


 

Tests supported by the Environmental Triaxial Testing System, static triaxial 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.

Axial Extension

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 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.

B Check

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.

Consolidated Drained (CD) Triaxial

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.

Consolidated Undrained (CU) Triaxial

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 (Triaxial)

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.

Constant Head Permeability

The constant head test simply maintains a constant differential in pressure between the top and the base of the specimen (top pressure is always set higher than the base pressure). The flow is then measured on the top controller and the base controller.  Please note: Some apparatus may require additional components or software modules to perform certain tests.

Constant Rate of Flow Permeability

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.

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.

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.

Local Strain Measurement

Accurate determination of soil stiffness is difficult to achieve in routine laboratory testing. Conventionally, stiffness of a triaxial test specimen is based on external measurements of displacement which include a number of extraneous movements.  By placing transducers directly on the sample, accurate measurements of strain may be obtained, particularly in the small strain area of the sample loading cycle where strain dependancy of soil stiffness (stiffer at low strains) can be otherwise be masked when using external transducers.

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.

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.

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.

Unconsolidation Undrained (UU) Triaxial

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.

Standards for the Environmental Triaxial Testing System, static triaxial testing equipment for soil testing :-