## 6 Discussion  
This study aims to investigate the mechanisms by which pit lake formation after open-pit mine closure affects slope stability, and to propose engineering-feasible slope stabilization strategies. The central hypothesis is that as the water level gradually rises, pore water pressure within the slope rock mass increases significantly, reducing effective stress and consequently diminishing slope stability. However, appropriately designed backfilling and toe-reinforcement measures can effectively enhance slope resistance to  
Figure 9: Contour of slope stability coefficients after mine closure with backfilling treatment of the open-pit mine: (**a**) after backfilling: water impoundment to -50 level; (**b**) after backfilling: water impoundment to +50 level.  
sliding. To test this hypothesis, the study employs high-resolution 3D geological modeling and unstructured mesh discretization, integrated with large-scale parallel mechanical computation and strength reduction theory, to simulate the spatial evolution of slope stability factors under different water impoundment scenarios and to assess the effectiveness of backfilling treatments.  
The numerical simulation results reveal a nonlinear decline in slope stability with rising water levels. Notably, when the impoundment reaches 0 m, the slope exhibits the largest extent of instability, with surface deformations extending up to 200 m from the pit edge. After the water level reaches 50 m, a slight recovery in slope stability is observed, attributed to the increasing hydrostatic pressure exerted by the water body, which provides passive support to the slope. These findings confirm the fundamental mechanical principle that elevated pore water pressure reduces shear resistance, consistent with previous studies on reservoir bank landslide evolution [1; 27; 28].  
Moreover, the proposed \"integrated backfilling combined with stepped toe reinforcement\" strategy effectively mitigates slope failure in the simulation, demonstrating promising engineering applicability. The novelty of this study lies in two key aspects: (1) the development of a high-fidelity 3D numerical model with 230 million elements, which, supported by a large-scale parallel computing platform, enables the first full-domain simulation of slope stability evolution in an open-pit mine; and (2) the design of a stepped toe backfilling approach for the soft-rock, high-angle northern slope, which simultaneously addresses environmental containment and mechanical stability, offering strong practical value and potential for broader application.  
Nevertheless, this study has certain limitations. First, the simulation focuses solely on the impact of rising water levels during the impoundment phase, without addressing the drawdown stage that may occur during lake operation due to regulation, pumping, or natural evaporation. Numerous engineering cases have shown that rapid water level decline can generate steep hydraulic gradients, leading to delayed pore pressure dissipation and increasing the risk of landslides and other geohazards [1; 27; 29]. In addition, some rock mass parameters in the current model were estimated based on literature or laboratory tests, which may differ from in situ conditions. Future work should incorporate field monitoring data and apply inverse modeling techniques to improve parameter accuracy and model reliability.  
Moreover, the slope's response to external disturbances such as seismic loading, long-term wet-dry cycling, and freeze-thaw effects should also be considered in future studies. In summary, this study provides theoretical insights and technical strategies for the dynamic evaluation and stabilization of pit slopes during post-closure water impoundment. However, further advancements are needed in multi-condition, multi-stage, and multi-source coupled modeling to more comprehensively support real-world engineering applications.