Damage constitutive model for soft rocks and its experimental verification on silty mudstone considering cyclic rock‒water interactions

Understanding the damage behaviors and mechanisms of soft rocks affected by rock‒water interactions is crucial for designing civil engineering structures and assessing geotechnical hazards. In this study, the physico-mechanical properties of silty mudstone subjected to wetting-dewatering cycles were investigated by P-wave velocity, three-dimensional scanning, and triaxial tests. The micro-mechanisms induced by rock‒water interactions were revealed using microscopic testing. The results indicate that mass, P-wave velocity, elastic modulus, peak strength, and cohesion of silty mudstone decrease with increasing wetting-dewatering cycles, while the internal friction angle follows a normal distribution. Wetting-dewatering cycles enhance the interface roughness of silty mudstone and reduce the plasticity index, leading to increased sliding friction. Continuous cycles exacerbate crack development and accumulation, weakening interlocking action and affecting energy dissipation. The dissipated energy rate serves as an indicator for crack stress thresholds, including crack closure, crack initiation, and crack damage stresses. The deterioration of silty mudstone strength primarily results from hydration-swelling softening and adsorption-fracturing driven by rock‒water interactions. Furthermore, a new constitutive model considering residual strength and nonlinear deformation characteristics was developed, effectively capturing the damage behaviors of silty mudstone under rock ‒ water interactions. The proposed model is also applicable to other types of rocks exhibiting similar damage mechanisms.