Characterization of the permeability evolution of hard and soft rocks under hydro‐mechanical coupling conditions

Abstract Prediction of permeability changes in surrounding rock induced by engineering disturbances is crucial for mitigating tunnel water inrush accidents. This study investigates the progressive failure characteristics and permeability evolution of hard and soft rocks subjected to triaxial compression. A series of laboratory tests were conducted at confining pressures ranging from 4 to 20 MPa. Experimental results demonstrate that rock permeability variation with strain shows three distinct stages: an initial decrease, a stage of rapid mutation, and a postpeak increase. The concept of critical permeability barrier strength is introduced, representing the stress level at which continuous fracture formation enables significant seepage. Furthermore, two generalized permeability–stress models are developed for soft and hard rocks. The predicted permeability values obtained from these models align well with the experimental data. These findings offer valuable insights into the hydro‐mechanical coupling behavior of rocks, providing a foundation for safe construction practices in underground engineering.