Stability Analysis of High and Steep Slopes Considering Fault in Abandoned Mine Pit-Converted Pumped-Storage Power Station Reservoir During Pre-Impoundment Stage

The transformation of abandoned open-pit mines into pumped-storage power station reservoirs offers an effective way to optimize China’s energy structure and supports China’s dual-carbon objectives by providing large-scale flexible storage. However, the steep slopes and complex geological conditions formed by mine excavation pose severe challenges to the stability of reservoir slopes. This paper focuses on a pumped-storage power station project converted from an abandoned mine pit in Luanping, Hebei Province. Specifically addressing high and steep slopes containing weak faults, it proposes a stability analysis method for the excavation stage that considers the influence of faults. The analysis assumes dry conditions, excluding reservoir-induced pore water pressure and seepage forces. Adopting the Janbu method and the M-P method within the limit equilibrium framework, safety analyses were conducted on multiple typical analysis sections of the abandoned mine pit before and after excavation. Analytical results indicate that the minimum safety factors derived from the Janbu method pre- and post-excavation are 1.33 and 2.13, respectively, whereas those obtained via the M-P method are 1.40 and 2.47. Given its consistently lower and thus more rigorous estimations, the Janbu method is recommended for conservative engineering design and risk assessment in similar geological settings. It is found that when the fault outcrop daylighting on the slope face constitutes a substantial spatial proportion, the potential sliding surface of the slope will extend from the top of the weak fault along an arc to the bottom of the stepped excavation. This indicates that the position of the fault influences both the sliding mode and the safety performance of the slope. The research findings of this paper could provide technical support for the slope engineering design, excavation and construction of pumped-storage power station reservoirs converted from abandoned mine pits.