True triaxial stresses mobilizing dilatant fracturing and engineering failure of hard rocks

Abstract

Rock dilation represents a nonlinear deformation and volume change, which can be quantified by the dilation angle, and plays a crucial role in the failure analysis of underground engineering. Traditionally, triaxial models describe the dilation angle as a function of confining stress and plastic shear strain. However, this study has uncovered a new mechanism governing true triaxial compressive fracturing, where dilatant fracturing is naturally mobilized by true triaxial stresses and significantly influenced by intermediate principal stress. The dilation angle has been observed to rapidly increase to a peak and then gradually decrease to a small value with increasing plastic shear strain. Additionally, as the minimum and intermediate principal stresses increase, the rate of change and peak value of the dilation angle decrease. Conversely, these features are reversed when the intermediate principal stress approaches or exceeds the uniaxial compressive strength of hard rocks. In light of these discoveries, based on previous research, a novel rock dilation angle (RDA) model is proposed to describe rock dilation behavior under true triaxial compression, where true triaxial stresses mobilize the dilation angle. The findings and proposed model demonstrate the true triaxial stress-dependent dilatancy behaviors in hard rocks, which are of significant importance for failure analysis in deep rock engineering.