Surface Subsidence Prediction Model in Deep Composite Lithologic Gangue Backfill Mining of Under the Coupling Effect of High Ground Stress and Water Environment

Under the coupling action of high ground stress and water environment, the physical and mechanical properties of backfill will change to some extent, and then secondary compression will occur. In this study, a prediction model of surface subsidence in deep filling mining was established through the combination of physical tests and theoretical analysis. First, the foundation coefficient of complex lithologic gangue under the coupling of high ground stress and water environment is determined, and then the prediction model of roof deflection in deep filling mining is established. Then, based on the hypothesis of conservation of subsidence space, the similarity theory and random medium theory are used to transfer the roof deflection to bedrock and the loose layer, and the accurate prediction of surface subsidence in deep filling mining is finally realized. The results show that the secondary compression of compound lithologic gangue under the influence of water environment is about 6.9%–8%. With Yingpanhao coal mine as the geological background, the relative errors of roof deflection, sandstone face of the Zhidan Group and loose layer are 1.5%, 1.1%, and 2.3%, respectively, which can accurately predict surface subsidence.