17 of

At any stage of loading the major principal stress is the all-round pressure 0'3 plus the intensity of deviator stress (0'1 - 0'3)' The actually applied stresses are the effective stresses in a slow test, that is 0'1 =0'/1 and 0'3 =0'/3' Dense samples fail along a clearly defined rupture plane whereas loose sand samples fail along many planes which result in a symmetrical bulging of the sample. The compressive strength of a sample is defined as the difference between the major and minor principal stresses at failure (0'1 - 0'3)" Typical shapes of dense and loose sand samples at failure are shown in Fig. 8.17.