Investigating Thermal-Hydro-Mechanical Coupling in Mudstones under Varied Thermal Cycles

Thermal loading significantly impacts the mechanical properties of mudstone, impacts which are crucial to understand for deep earth engineering applications such as geological disposal of radioactive waste, compressed air storage, geothermal energy, and underground coal gasification. This study analyses the response of Sidmouth Mudstone, part of the Mercia Mudstone Group, under triaxial compression with varied thermal loading conditions. Experiments were conducted at natural moisture contents across one and three thermal loading cycles to 90°C, with confining pressures of 5 MPa, at both 90°C and room temperature. The results indicate that under triaxial compression at 90°C, regardless of the number of thermal cycles, Sidmouth Mudstone exhibits a Poisson’s Ratio comparable to water and displays extremely brittle post-peak behaviour compared to room temperature conditions. After three thermal cycles at 90°C, the mudstone shows a higher fracture density. Triaxial strengths of 9 MPa and 24 MPa for tests at 90°C and room temperature, were recorded respectively. The primary mechanism driving the response is proposed to be thermal-hydro-mechanical coupling, where induced pore pressure from thermal expansion causes localised strain and propagating thermally induced fractures. This research contributes to understanding the response of mudstones under thermal loading and the magnitude of thermal-hydro-mechanical coupling effects.