A Small True Triaxial Apparatus with Wave Velocity Measurement

This paper describes a new cubical, true triaxial apparatus recently developed at the University of Western Australia (UWA). The apparatus is a stand-alone unit of the rigid type, where three pairs of pistons can be pressurized to impose three independent, rectilinear stresses on a sample of 250 mm side length. The sample can be tested either dry or saturated. Both drained and undrained shearing can be carried out with maximum pressure of about 1.5 MPa and maximum linear strain of about 8% in any of the three principal directions. A wave velocity measurement system is incorporated so that both elastic shear (Vs) and compression (VF) wave velocities can be measured, with the wave travelling between any two opposite faces of the device, or along skew paths. The elastic waves are generated and detected using "in house" manufactured wave transducers, which can access the sample externally. This feature enables the shear transducers to be rotated 90° degrees to change the polarization direction, enabling Vs to be measured in inclined planes. Additionally, the device enables accurate measurement of Ko. The paper presents results obtained from a silica sand to show the capability of the new device.