Mechanical behavior and damage constitutive model of silty mudstone under thermo-hydro-mechanical interactions

Understanding the deterioration behaviors and mechanisms of rocks under thermo-hydro-mechanical (THM) interactions is crucial for mitigating slope instability. In this study, the physico-mechanical properties of silty mudstone subjected to THM interactions were investigated by triaxial tests. The underlying micro-mechanisms were revealed using microscopic tests. The triaxial test results indicate that the strength parameters of silty mudstone decrease by 89.50% (deformation modulus), 78.15% (peak strength), 70.58% (cohesion), and 48.65% (friction angle) under 16 THM cycles, a load of 300 kPa, and alternating between 0℃ water immersion and 60℃ drying. The SEM test results indicate that the deterioration of silty mudstone strength primarily results from hydrothermal-expansion softening and cracking driven by the TLHM interactions. The specimens manifest shear failure under confining pressure exceeding 140 kPa. Furthermore, a new constitutive model considering hydrothermal-expansion strain and non-linear deformation characteristics was developed. The discrepancy between the experimentally measured peak strength and the damage constitutive model prediction remains below 5%. The proposed model is verified to be in satisfactory agreement with the experimental results. The self-designed THM apparatus overcomes the limitations of traditional investigations, enabling simultaneous consideration of thermal, hydraulic, and mechanical interactions.