Coupled Plasticity and Damage Constitutive Model Considering Residual Shear Strength for Shales

Abstract

Shales are the most common materials on the Earth's surface that are frequently encountered in various energy, environmental, and engineering applications. Numerically predicting the mechanical behavior of shales is of great importance in the geomechanics community. A coupled plasticity and damage constitutive model is developed in this study to describe the mechanical behavior of shales that spans the prepeak, peak, and postpeak regions. A concept of a damaged part of geomaterials, which possesses residual shear strength, is introduced in the proposed model. A thermodynamic conjugate force is presented by accounting for the residual shear strength of the damaged part. Procedures to determine the model input parameters and an algorithm to implement the constitutive model in a numerical code are presented. Validation against experimentally observed stress–strain curves of shales shows that the proposed model can predict the mechanical behavior of shales under various stress paths and confining stresses from the pre- to postfailure regimes.