The main objective of this study regards the analysis of results of a series of compressive strength tests on granite rocks carried out on a press with servo-controlled loading in order to characterize their strain-softening behavior. We pay particular attention to the evolution of failure criteria from peak to residual strength that obviously presents plastic strain dependence. A graphical methodology was used to link strength with plastic strain all along the process of plastic yield and for different levels of confining pressure. It was possible to fit a mathematical expression, which is able to reflect this relation and which also allows obtaining evolving strength criteria (cohesion and friction values). We have also accounted for the post-failure dilation behavior of these rocks, studied elsewhere. The derived model has been implemented in a numerical code, and some simple simulations are carried out. These models have been able to reproduce the initial experimental results reasonably well.
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