Experimental and numerical investigations on failure process and permeability evolution of weathered granite under hydro-mechanical coupling

Rock-breaking is a fundamental process in subsea tunnel construction, particularly during deep trench excavation. Understanding the failure process and permeability evolution of rock masses under hydro-mechanical coupling is essential for optimizing excavation plans and ensuring construction safety. Due to the challenges of capturing crack propagation and permeability evolution solely through experiments, numerical simulations provide a valuable supplement. This study investigates the weathered granite from the deep section of the Shenzhen-Zhongshan Bridge subsea tunnel, employing triaxial compression tests and CFD-DEM numerical simulations under hydro-mechanical coupling conditions. The experimental results reveal that the stress-strain curves can be divided into five distinct stages, with plastic strain increments becoming more concentrated as confining pressure and fluid pressure increase, particularly after the peak strength stage. Numerical simulations further demonstrate that higher confining pressure promotes shear failure, while elevated confining and fluid pressures accelerate the formation of stable microcracks. Contact forces and seepage forces are predominantly concentrated around the primary cracks, with contact forces distributed uniformly along the crack path and seepage forces most pronounced at the inlets and outlets of the seepage channels. These findings offer significant insights into the internal hydro-mechanical behavior of rocks, contributing to the refinement of rock-breaking strategies and the mitigation of geological risks in subsea tunnel construction projects.