Thermal cycling-induced degradation of carbonaceous mudstone soft interlayers: Energy dissipation-driven shear strength prediction

Although thermal cycling critically affects the long-term stability of mining slopes by inducing progressive damage in carbonaceous mudstone soft interlayers, conventional stability models neglect this thermoclimatic feedback and lack reliable predictive frameworks. This study clarifies the underlying damage mechanisms under thermal cycles within the land surface temperature range of −10 °C to 65 °C and establishes a physics-based model for predicting shear strength degradation. We combine backscattered electron microscopy and energy-dispersive X-ray spectroscopy for microstructural characterization, direct shear testing, and quantitative image analysis of specimens exposed to up to 16 thermal cycles and develop a theoretical yield-strength model based on the principle of minimum energy dissipation. The results confirm a three-stage damage evolution controlled by mineral thermal expansion mismatch: interface debonding during initial cycles, two-dimensional crack networking during intermediate cycles, and three-dimensional crack penetration with self-accelerating failure in later cycles. Mechanical degradation nonlinearly depends on the number of thermal cycles, characterized by substantial reductions in cohesion and shear modulus, alongside a more moderate decrease in the friction angle. The developed model captures these nonlinearities, revealing that strength degradation is governed by the irreversible accumulation of energy dissipation and achieving higher predictive accuracy than conventional extrapolation methods. This multiphysics-coupled framework establishes a micro-to-macro link in thermal damage processes and provides a robust basis for the lifecycle stability assessment and climate-resilient design of slopes containing soft interlayers. • Extreme thermal cycling (−10 °C to 65 °C) enhances long-term damage in mining slopes • Atmospheric thermal fluctuations damage carbonaceous mudstone soft interlayers • Analysis reveals mineral-specific thermal expansion mismatch-driven cracking • Shear modulus and cohesion degradation dominate nonlinear strength loss • Minimum energy dissipation-yield strength model predicts cumulative slope risk