TRIAXIAL TESTING APPARATUS

In a Triaxial shear test, stress is applied to a sample of the material being tested in a way, which results in stresses along one axis being different from the stresses in perpendicular directions.

This is typically achieved by placing the sample between two parallel platens, which apply stress in one (usually vertical) direction, and applying fluid pressure to the specimen to apply stress in the perpendicular directions.

This is done by our testing apparatus which allows application of different levels of stress in each of three orthogonal directions X, Y, Z Axis are discussed below, under “True Triaxial test”.)

The application of different compressive stresses in the test apparatus causes shear stress to develop in the sample; the loads can be increased and deflections monitored until failure of the sample.

From the Triaxial test data, it is possible to extract fundamental material parameters about the sample, including its angle of shearing resistance, apparent cohesion, and dilatancy angle.

These parameters are then used in computer models to predict how the material will behave in a larger-scale engineering application. An example would be to predict the stability of the soil on a slope, whether the slope will collapse or whether the soil will support the shear stresses of the slope and remain in place.

Consolidated Drained (CD)

In a ‘consolidated drained’ test the sample is consolidated and sheared in
compression slowly to allow pore pressures built up by the shearing to
dissipate. The rate of axial deformation is kept constant, i.e., strain is
controlled. The idea is that the test allows the sample and the pore
pressures to fully consolidate (i.e., adjust) to the surrounding stresses.
The test may take a long time to allow the sample to adjust, in particular
low permeability samples need a long time to drain and adjust strain to
stress levels.

Consolidated Undrained (CU)

In a ‘consolidated undrained’ test the sample is not allowed to drain.
The shear characteristics are measured under undrained conditions
and the sample is assumed to be fully saturated. Measuring the pore
pressures in the sample (sometimes called CUpp) allows approximating
the consolidated-drained strength. Shear speed is often calculated based
on the rate of consolidation under a specific confining pressure (whilst
saturated). Confining pressures can vary anywhere from 1 psi to 100 psi
or greater, sometimes requiring special load cells capable of handling
higher pressures.

Unconsolidated Undrained (UU)

In an ‘ unconsolidated undrained’ test the loads are applied quickly, and the sample is not allowed to consolidate during the test. The sample is compressed at a constant rate (strain-controlled).

Our Triaxial Test System provides automated triaxial compression tests on cylindrical undisturbed and remoulded soil samples. Unconsolidated undrained (UU), consolidated drained (CD) and consolidated undrained (CU) compression tests can be automatically run, controlled and reported using this
apparatus.

The Triaxial Testing Apparatus consists of a 50 KN capacity Load Frame, Platen adaptors, dial gauge or digital transducer assembly, Triaxial Cell, Base and pressure system.

The Triaxial Testing Apparatus provides variable speed from 0.399999”(9.99999 mm) per minute to as low as 0.000001” (0.00001 mm) per minute.

An electronic control system with touch-sensitive keypad for precise setting, control and viewing of all load frame functions.

The Data Acquisition and Controls System (DA/CS) for automated data acquisition and recording of test parameters supplied with a complete set of Electronic Measurement, Transducers for load, displacement, pressure and volume change.

The Triaxial Software for recording, analysis and report generation, master control panel and de-aired water tank system for precise applications of confining, back and saturation pressures.

Oil and Water Constant Pressure System

The Oil and Water Constant Pressure Unit is extremely versatile and can be used in conjunction with a wide range of test equipment. The unit provides continuous variable pressure up to 1700
kPa. The pressure is increased or decreased simply by turning a control knob.

The Unit is used for providing cell/backpressure in triaxial tests. The apparatus is supplied without a gauge for those customers who have suitable pressure monitoring equipment.

As optional equipment for monitoring the pressure:
• The Digital Pressure Gauge
• The pressure transducer
The machine features a clear hydraulic/water interface reservoir and up to 1 liter capacity of water is available under pressure. Supplied complete with 2 liters of No.46 regular hydraulic oil.

Automatic Volume Change Unit

The Unit consists of a piston connected to a 25 mm travel linear transducer which is sealed against a precision machined calibration chamber so that the linear movement of the piston is
exactly proportional to the volume of water in the calibration chamber.

The apparatus creates an electrical signal proportional to the volume of water flowing through the unit. By connecting it to the data acquisition system the measured volume change will be
used by software during the test and in final report.

Capacity : 100 cm³

Transducer Input : up to 12 V DC

Accuracy : ± 0.1 ml

Pressure Transducer and Block for Triaxial Test Cells

The Pressure Transducer is used for the measurement of cell or back or pore pressure of water in triaxial test systems and also should be used with a Control Unit or a data logger

The Block for triaxial test cells is used for connection of the pressure transducers and de-airing in the water hoses.

De-Airing Water Systems

The De-Airing Water Apparatus is a compact and self-contained equipment which can de-air water quickly and efficiently down to levels of dissolved oxygen acceptable for geotechnical test methods.
The apparatus used in conjunction with the de-airing tank. Air is removed from the water by a vacuum system. De-airing tank should be ordered separately.

The first option for de-airing water;
• De-Airing Water Apparatus
• De-Airing Water Tank
• Vacuum Control and Water Connection Panel with Regulator and Vacum Gage Manometeror Connection Panel for Vacuum and Water with Vacuum Gage(These panels are optional)
• Plastic Hose

The second option for de-airing water:
• Vacuum Pump
• Filter Flask or Air Drying Unit / Water Trap
• De-Airing Water Tank
• Vacuum Control and Water Connection Panel with Regulator and Vacum Gage Manometeror Connection Panel for Vacuum and Water with Vacuum Gage(These panels are optional)
• Plastic Hose

By using Vacuum Control and Water Connection Panel, vacum pressure degree can be regulated.

By using de-airing water equipment can be used without repeated assembling the hoses.

Triaxial Cells

The cell has been designed and treated to minimize corrosion. Particular attention has been paid to the quality of finish between the piston and the head. Final assembly includes the fitting of an O-ring seal and the use of a special lubricant to reduce friction to a minimum and eliminate water leakage. The piston load capacity is designed to accept high axial loads which may be present during the final stages of a test.

Each cell has five take-off positions drilled in the base for top drainage/back pressure, pore water pressure and bottom drainage. Three no volume change valves and anvil for displacement transducer are supplied complete with the cell. Each cell will accept a range of base adaptors and various accessories for testing a wide range of specimens.

The cell capacity is designed to tolerate confining pressures as high as 1700 kPa which is enough for simulating most in-situ conditions.

For cell accessories and sample preparation accessories see next page.

Cell Accessories

Sample Preperation Accessories