Shear-creep-induced strength degradation of soft–hard interbedded rock masses controlled by layer-thickness ratio: implications for progressive failure of anti-dip slopes

Abstract

Anti-dip slopes with gently dipping soft–hard interbedded strata (GD-SHIS anti-dip slopes) may exhibit relatively high resistance under short-term cross-layer shearing. However, sustained shear loading can induce soft-layer deformation, shear-parameter degradation, and delayed progressive failure. Here, soft–hard interbedded rock-like specimens with different layer-thickness ratios were prepared using the Heishan open-pit coal mine as the engineering prototype. Uniaxial compression tests, digital image correlation–acoustic emission monitoring, combined shear-creep and post-creep direct shear tests, and slope-scale numerical analyses were conducted to clarify layer-thickness-ratio-controlled failure transition and shear-creep-induced strength degradation. As the layer-thickness ratio decreases from 4:1 to 2:3, peak strength and elastic modulus decrease by approximately 26.3% and 40.4%, respectively. Meanwhile, the failure mode changes from hard-layer-dominated tensile splitting to soft-layer- and interface-controlled inclined shear failure. The proportion of shear acoustic-emission events increases from 16.4% to 43.2%. After shear creep, cohesion shows stronger degradation sensitivity than the internal friction angle, and higher soft-layer content markedly shortens the stable holding duration under high creep shear stress. A deformation-based creep damage variable, D t , was introduced to convert different stress–time creep histories into comparable strength-reduction states and to establish a D t − c − φ relationship. Slope-scale simulations reveal a dual-control mechanism: slope angle primarily governs the shear driving force and damage-accumulation rate, whereas layer-thickness ratio governs the spatial continuity of weakened paths along soft layers and interfaces. These findings provide an experimental basis for time-dependent shear-parameter reduction and long-term stability assessment of GD-SHIS anti-dip slopes.

The authors' abstract, as published at the source. International Journal of Rock Mechanics and Mining Sciences, 2026 · DOI ↗