Determination of confinement and plastic strain dependent post-peak strength of intact rocks

The post-peak strength behavior of rocks is important for stability analysis of underground excavations. This paper studies the confinement and plastic strain dependent post-peak strength of intact rocks. First, the post-peak behavior of rocks is studied by conducting triaxial compression tests on a coarse marble. The post-peak strengths of the rock under different confining pressures and plastic strains are obtained using the recorded stress-strain curves. A strength degradation index is then proposed to represent the post-peak strength degradation, and a negative exponential function, which includes a shape parameter n, is used to describe the relation between the strength degradation index and the confining pressure. Parameter n is plastic strain dependent, which decreases with the increase of plastic strain. The proposed strength degradation model can well capture the post-peak strength envelopes of the coarse marble under different plastic strains. Finally, two sets of triaxial compression test data from previous studies are used to further verify the strength degradation model. The peak and post-peak strength behaviors of two marbles are well represented using the proposed model. The approach proposed in this study also provides a simple yet useful method for determining the realistic residual strength of intact rocks.