Evaluation of impact of surface dynamic subsidence on construction of pumped storage hydropower plants in abandoned open-pit mines

Surface dynamic subsidence is one of the key scientific issues that need to be solved urgently when constructing pumped storage hydropower plant in abandoned mines. In order to explore the impact of surface dynamic subsidence on the stability of pumped storage hydropower plant in abandoned open-pit mine during construction and operation, Haizhou abandoned open-pit mines were used as the research background, the mechanism and characteristics of surface subsidence affected by the combined underground and open-pit mining were revealed, and a surface dynamic prediction model was established based on Knothe time function. The creep parameters of rock and soil in the Haizhou open-pit mining area were inverted and sensitivity analyzed, and the surface subsidence laws in different periods of combined underground and open-pit mining were studied. The distribution of subsidence hazards in the area where the pumped storage power station is located from 2020 to 2120 is analyzed. Finally, the stability of the pumped storage hydropower plant during construction and operation was evaluated. Research indicates: The influencing factors of surface subsidence include coal seam inclination angle, coal seam burial depth, mining thickness, slope angle and goaf spatial distribution. The maximum subsidence value, influence range and duration are all greater than a single underground mining. The modified Knothe time function model that comprehensively considers the interaction between underground and open-pit mining can more accurately predict surface dynamic subsidence. The three-dimensional numerical calculation model of combined underground and open-pit mining based on the CVISC creep model has high applicability and accuracy. The minimum distances between the upper reservoir and pumping pipeline from the affected area are 254.9 m and 15.1 m respectively, and the semi-ground powerhouse is located within the affected area. The use of grouting filling to treat gobs can effectively control the impact of surface dynamic subsidence (reducing the subsidence value by 85% on average). It is feasible to build a pumped storage hydropower plant in an abandoned Haizhou open-pit mine. The research results are of great significance for sustainable prediction of surface dynamic subsidence, prevention and control of geological disasters, and development of remaining resources in abandoned open-pit mines.