Brittleness evaluation and damage evolution of sandstone under hydromechanical coupling

Investigating the brittleness characteristics and damage evolution of deep rock masses under hydromechanical coupling has important significance. The variations in mechanical properties and brittleness characteristics of sandstone under different confining pressures and pore pressures were studied. Based on the stress threshold evolution and energy conversion analysis of the full stress-strain behavior characteristics of the rock, the new brittleness evaluation indexes were proposed, which effectively described the rock brittle failure mode and verified the reliability and applicability of the brittleness index. Additionally, from the perspective of rock pore micro-elements and the growth of matrix particle defects, the strain statistical damage theory was introduced to establish a rock statistical damage evolution model capable of accounting for the influence of pore pressure, thereby effectively capturing the nonlinear soft hardening of porous rocks under hydraulic coupling conditions. The correlation between rock brittleness and rock soft and hardening characteristics was reasonably expressed by constructing a new brittleness evaluation index, discovered from the relationship between rock damage parameters and brittleness characteristics. Eventually, based on the proposed nonlinear expression and statistical damage evolution model, the development trend of sandstone lateral strain is predicted well. The theoretical validation has good consistency with the experimental data and illustrates the rationality of the model.