In the framework of classic elastoplasticity theory

it is assumed that rock material abides by the Mohr-Coulomb yield criterion and its plastic deformation obeys the non-associated flow rule during the process of strain softening. The strength parameters before and after the peak are obtained by analyzing the strain-softening behaviors of two sets of rocks in the triaxial tests. The piecewise linear approximation is made when numerical analysis is performed under the framework of the classical theory of plasticity. Then the strain-softening stage in the post-peak part of stress-strain curve can be simplified into a series of brittle-plasticity process. The stress-strain curve

lateral strain-axial strain curve

volumetric strain-axial strain curve and plastic volumetric strain-axial plastic strain curve are acquired by adopting the given strength parameter evolution laws and the strain-softening simulation method. The obtained stress-strain curves are in good agreement with those by the experiment

and the other curves are in the similar variation to those observed in experiments. The presented method and the results show that it is meaningful for determining strength parameters and studying the evolution law of the post-peak strength from laboratory test.