Rainfall-induced seepage damage coupling mechanism and stability evaluation of high and steep slopes in deep open-pit mines

Abstract

Steep, highly fractured rock slopes, characterized by lithological heterogeneity, intense fracturing, and sensitivity to rainfall-induced hydraulic perturbations, pose challenges that are not covered by classical sliding-surface models. This study integrates multiphysics monitoring, laboratory experiments, and probabilistic inversion to investigate a representative slope at the Luanchuan Longyu open-pit mine. A positive feedback loop was found between seepage and fracture development: elevated pore pressure induced by rainfall or increased groundwater levels drives fracture propagation, enhances permeability and seepage velocity, reduces effective stress, and initiates a self-accelerating “seepage → fracture → rock weakening” chain, even in the absence of a continuous slip surface. Lithological analysis reveals that marble and gneissic granite exhibit high strength (UCS ≈ 57-58 MPa, c ≈ 6.2-6.8 MPa, ϕ ≈ 39°-43°), whereas quartz-mica schist is a highly weathering-sensitive weak layer (saturated UCS = 9.78 MPa, with 35 % strength loss and SDI = 58.96 % after 11 wetting-drying cycles). Parameter back-analysis (with 80 % confidence intervals) reveals schist ( c = 24.5 kPa, ϕ   = 34.4°) as the dominant weak stratum and faults ( c   = 8.9 kPa) as potential slip surfaces, clarifying the lithology-structure controls on failure patterns. Rainfall infiltration triggers a nonlinear hydraulic response and preferential toe flow, causing pore pressure to propagate downward and shifting slope degradation from surficial to whole-slope failure-a dynamic "surface-to-depth" progression modeled in this study. These findings provide a quantitative mechanistic framework for assessing steep, heterogeneous slopes and support intelligent hazard mitigation through rainfall thresholds and real-time monitoring.