Mechanical response of a rock mass with parallel double fissures under the coupled action of fracture water pressure and fissure inclination angle

Abstract

Existing studies on hydro-mechanical coupling in fractured rock masses have mostly focused on a single fracture or a single influencing factor, and there remains a lack of systematic understanding of the mechanical response and governing mechanisms of parallel double-fissure structures under the synergistic effects of water pressure and inclination angle.To investigate the mechanical response of rock specimens containing parallel double fractures with fixed fracture spacing under the coupled effects of fracture water pressure and fracture inclination angle, numerical simulations were conducted using COMSOL Multiphysics. The peak stress, crack propagation, failure modes, and internal fluid pressure evolution of specimens under various loading conditions were systematically analyzed. The main conclusions are as follows: (1) Within the investigated two-dimensional parallel double-fracture model with fixed fracture spacing, peak stress generally decreases with increasing fracture water pressure but increases with fracture inclination, indicating a weakening effect of water pressure on specimen load-bearing capacity. (2) Peak stress exhibits an approximately linear relationship with fracture water pressure, with R2 values ranging from 0.85054 to 0.99695. The absolute fitted slope increases from 1.206 at 0° to 3.753 at 90°, indicating greater sensitivity to water pressure at higher fracture inclinations. (3) Fracture water pressure and inclination jointly affect peak stress. The minimum peak stress is 2.42 MPa at 0° and 3 MPa, whereas the maximum is 8.44 MPa at 90° and 1 MPa. (4) Fracture inclination influences crack initiation, propagation, and coalescence. At higher inclinations, cracks are more concentrated near fracture tips and rock bridges, accompanied by faster damage accumulation and more abrupt failure. (5) Internal fluid pressure is non-uniform and locally concentrated near fracture tips, rock bridges, and highly damaged regions. The spatial correspondence between crack and pressure distributions indicates spatial coupling under the simulated conditions.