Renewed instability assessment and reinforcement evaluation of a landslide-affected waste dump slope under adverse hydraulic conditions

Abstract Waste dump slopes may appear stable after an initial landslide, yet their renewed instability potential under subsequent hydraulic disturbance can remain significant. This study investigates a landslide-affected waste dump slope in Ma’anshan City, Anhui Province, China, by integrating pre-landslide and post-landslide UAV-based three-dimensional reconstruction, CAD-derived representative profiles, field investigation, and measured pre-failure rainfall data. Two-dimensional coupled seepage-stability models were established in Midas GTS NX, and the shear strength reduction method was used to evaluate slope responses under pre-landslide natural and rainfall-infiltration conditions, post-landslide natural and surface-reaching phreatic-line conditions, and reinforced conditions. The results show that, under the adopted upper-bound effective infiltration ratio, the factor of safety of the pre-landslide slope decreased from 1.17 under natural conditions to 0.98 after the recorded rainfall process, indicating that the slope could evolve from a low-reserve stable state to a near-limit or unstable state under high effective infiltration. After the initial landslide, the reconfigured slope reached temporary equilibrium with a factor of safety of 1.55 under natural conditions, but decreased to 0.92 under the prescribed surface-reaching phreatic-line scenario, revealing its conditional renewed-instability potential under an upper-bound hydraulic state. The numerically interpreted instability-controlled section showed good profile-scale agreement with the UAV-derived landslide morphology, with a rear-scarp offset of 0.3 m and a main affected-zone length error of 7.7%. For the reconfigured residual slope, a stabilization scheme dominated by prestressed anchor cables and assisted by local shallow bolts increased the factor of safety to 2.28 under natural conditions and 1.28 under the surface-reaching phreatic-line scenario. The proposed framework provides a practical basis for post-landslide reassessment and residual slope stabilization of rainfall-sensitive waste dump slopes.