Water-Induced Shear-Strength Degradation of Coal-Measure Rocks and Its Engineering Implications: A Case Study of the Fushun West Open-Pit Mine, China

Abstract

Slopes excavated in coal-measure strata are prone to rainfall-induced landslides because water-induced disturbances progressively degrade rock-mass shear strength. This study investigated six coal-measure lithologies from the unloading zone of the Fushun West Open-Pit Mine using triaxial compression tests after separate wetting–drying and continuous-immersion treatments. Condition-dependent cohesion, c, and internal friction angle, φ, were fitted with exponential functions and incorporated into the Mohr–Coulomb criterion. For scenario analysis, the retention ratios measured in the two separate treatment series were applied sequentially in a separable empirical parameterization. This no-interaction approximation was used to update coal-measure strength inputs in representative slope models. Cohesion and φ decreased exponentially within the tested ranges, with in-sample R2 values greater than 0.85, and cohesion was generally more sensitive. Continuous immersion produced rapid early softening, whereas wetting–drying cycles produced cumulative deterioration. Limit-equilibrium and finite-element calculations showed lower safety factors and more concentrated deformation under more severe parameter-reduction scenarios. Model-specific cumulative-displacement reference values of 52.36–213.82 mm were paired with Fs levels of approximately 1.15, 1.05, and 1.00 and compared qualitatively with historical monitoring curves. The findings provide a reference for rainy-season slope-stability prediction and staged warning in open-pit coal mines.