Fatigue Mechanisms of Porous Rocks Subjected to Cyclic Pore Pressures: Insights from Hydro-Mechanical Phase-Field Simulations

In this work, we formulate a hydro-mechanical phase-field model to investigate the fatigue failure behavior of porous rocks under cyclic pore-pressure loading. Our phase-field model integrates pore-pressure diffusion, fatigue-induced degradation of failure resistance, and breakage constitutive laws into a unified framework for capturing deformation, damage evolution, and failure progression in saturated porous rocks. The distinctive features of our model include (i) a hydro-mechanical coupling formulation that captures the interaction between fluid diffusion and solid deformation; (ii) a fatigue degradation mechanism that describes the progressive reduction of failure resistance under repeated pore-pressure disturbances; and (iii) a breakage constitutive relationship that allows the transition from diffuse compression-dominated damage to mixed-mode compression-shear strain localization. We first present several numerical benchmarks, including hydro-mechanical fracture, cyclic fatigue, and triaxial compression tests, for validation. Then, the underlying fatigue mechanisms of porous rocks are investigated through a series of numerical examples subjected to cyclic pore-pressure loading. This work not only helps improve our understanding of the fatigue mechanisms of porous rocks, but also provides a useful numerical tool for predicting hydraulic fatigue degradation in rock engineering.