Effects of high differential stress and mineral properties on deformation and failure mechanism of hard rocks

Abstract

To study the deformation and failure mechanism of hard rocks, true triaxial compression tests were conducted on four types of hard rocks to obtain the complete stress–strain curves and failure modes. Under true triaxial compression conditions, the shapes of the complete stress–strain curves can be divided into three types: elastic–brittle (EB), elastic–plastic–brittle (EPB), and elastic–plastic–ductile (EPD) types. According to the different post-peak deformation behaviours, the stress–strain curves of EPB type can be subdivided into three sub-categories: post-peak instantaneous brittle (EPB-I), post-peak multi-stage brittle (EPB-M), and post-peak delayed brittle (EPB-D). The stress–strain curves change from EPD to EPB-D, EPB-M, EPB-I, and finally EB with increasing differential stress (σ2– σ3). The deformation characteristics are dependent on intermediate principal stress σ2, minimum principal stress σ3, mineral compositions, and mineral textures of rock samples. An increase in σ3leads to an increased ductility, while an increase in σ2leads to an increased brittleness. Moreover, rocks with regular mineral textures and low mineral hardness are more prone to ductility. When the deformation curve is transformed from EPD to EPB and then to EB, the tensile crack gradually predominates, and the macroscopic failure angle gradually becomes steeper.