Advanced Dynamic Triaxial Testing System

Product Code : DYNTTS

The Advanced Dynamic Triaxial Testing System is a high-end, no compromise testing apparatus combining a triaxial cell with a dynamic actuator capable of applying load, deformation and stresses up to 5Hz. The cell itself is screw-driven from an integral base unit housing the motor drive. Axial force and axial deformation are applied through the base of the cell.  The system can be combined with a dynamic cell pressure actuator such that cell pressures may also be applied dynamically up to fundamental frequency of 5Hz.

Discover more dynamic triaxial testing equipment for soil testing.

Key features Benefits to the user
High accuracy electro-mechanical control: The DYNTTS system is capable of very small strain static tests through to large strain dynamic tests.
Interchangeable load cells: Allows user to accommodate very soft to very stiff soils with ranges of 1, 2, 4, 8, 10, 16, 25, 40 and 60kN.
In-built balanced ram (up to 5Hz systems): Keeps cell pressure constant during cycling, meaning a dynamic pressure controller is not required (unless dynamic cycling of cell pressure is required).
Interchangeable pedestals and triaxial extension top caps: Allows testing of 38, 50, 70 and 100mm diameter test specimens in the same cell.
Direct closed loop of axial displacement & axial force: Accurate control in either axial displacement or axial force mode.
Actuators

High accuracy electromechanical

Axial Force Accuracy

<0.1%

Axial Force Accuracy

24bit (i.e. <0.4N for 10kN load cell, <1.5N for 40kN load cell)

Axial Load

10, 40 or 60

Computer Interface

USB

Displacement Range

100mm

Displacement Resolution

0.20um

Operating Frequency (Hz)

5

Pressure Range (MPa)

2, 4

Sample Sizes

38, 39.1, 50, 61.8, 70, 100, 101, 150, 300mm

  • Temperature Controlled Testing: -10°C to +60°C, -20oC to +65oC,  -20°C to +85°C (The heater and chiller units used have a resolution of 0.01°C with a bath stability of +/-0.05°C, this stability & resolution is not necessarily reflected in the cell).
  • Available in 10kN, 40kN or 60kN.
  • Optional upgrade to cell capable of taking 150mm samples.
  • Optional cell upgrade from 2MPa (standard) to 4MPa
  • Bender Element System (Vertical, Horizontal, S and P waves)
  • Hall Effect local Strain
  • LVDT Local Strain
  • Unsaturated Testing

 

Tests supported by the Advanced Dynamic Triaxial Testing System, dynamic 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.

Dynamic Cyclic Axial Stress Capability

Dynamic cyclic axial stress is an extremely advanced test, only available on dual axis advanced dynamic triaxial testing systems.  During the cyclic loading the area of the sample is continuously calculated allowing the sample stress to be accuratelly maintained at the desired amplitude and wave-shape.

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 (Dynamic)

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

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.

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.

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.

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.

Standards for the Advanced Dynamic Triaxial Testing System, dynamic triaxial testing equipment for soil testing :-