Triaxial Test

Abstract

The failure of a soil sample under shear could perhaps best be investigated in a laboratory test in which the sample is subjected to pure distortion, at constant volume. The volume could be kept constant by taking care that the isotropic stress $\sigma _{0}=\frac{1}{3}(\sigma _{1}+\sigma _{2}+\sigma _{3})$ remains constant during the test, or, better still, by using a test setup in which the volume change can be measured and controlled very accurately, so that the volume change can be zero. In principle such a test is possible, but it is much simpler to perform a test in which the lateral stress is kept constant, the triaxial test. In order to avoid the complications caused by pore pressure generation, it will first be assumed that the soil is dry sand. The influence of pore water pressures will be considered later.