Excess pore pressure generation potential within shear zone by means of ring shear tests

Abstract

Excess pore pressure generation potential within shear zone by employment of the ring shear tests have been investigated on the saturated samples which have quite different grain crushing susceptibility. In naturally drained tests, the sample the grains of which are crushable showed the great reduction of apparent internal friction during shearing to generate rapid flow phenomena. Based on the results of permeability and grain size analyses, it is estimated that the crushed particles formed the less-permeable shear zone and excess pore pressure generation rate exceeded the dissipation rate to yield flow behaviour, and it occurred heavily in high shear speed or normal stress tests. And to express the susceptibility of the samples against flows, the new parameter “potential for rapid flow phenomena” was proposed as the ratio of internal friction angle (φm) to apparent friction angle (φa).In order to estimate the excess pore pressure in undrained condition from the drained tests, the concept of “equivalent normal stress” was introduced as the ratio of volumetric strain to the compressibility. Equivalent normal stress using compressibility which was obtained by changing normal stress during shearing was almost equal to excess pore pressure at the same shear displacement up to 1 m at which steady state was reached. And Excess pore pressure ratio in undrained tests and the logarithm of equivalent normal stress divided by normal stress with compressibility obtained during consolidation process showed the linear relationship.