A Unified Constitutive Model for Rock Based on Newly Modified GZZ Criterion

This paper proposes a unified constitutive model for rock based on the newly modified generalized Zhang-Zhu (GZZ) criterion. The constitutive model adopts a non-associated plastic flow rule and a continuous potential function that takes the three effective principal stresses into account. To reflect strain-softening, strain-hardening, and elastic-perfectly plastic behavior of rock in a unified way, a general expression is proposed to model the post-failure behavior of rock using the deviatoric plastic shear strain as the fundamental variable. The proposed constitutive model has been successfully implemented in a 3D finite-difference code and validated using it to simulate the true triaxial test of two types of rocks and comparing the simulation results with the experimental data. Finally, a 3D numerical model based on the proposed constitutive model is constructed to simulate a highway rock tunnel during construction. The results show that the predicted displacements of the rock tunnel are in good agreement with the field measurements.