Failure depths of stope floors under dynamic loading induced by roof breaking

ObjectiveAccurately assessing the failure depths of stope floors is crucial for assessing floor water inrush risks. Conventional theoretical models for calculating the failure depths generally merely consider static loads from the support pressure and confined water's pressure in stopes, leading to large deviations between calculation results and actual situations. Therefore, constructing a more practical computational model that comprehensively considers the coupled effects of multiple force sources on the failure of deep floors can provide a scientific basis for the effective prevention and control of water hazards in deep coal seam floors. MethodsBased on the dynamic elasticity theory and the loads on a stope floor during roof weighting, this study constructed a computational model for the mechanical responses of the stope floor under combined static and dynamic loads. Using this model, this study determined the law of the transfer of dynamic load stress in the floor, as well as the dynamic response characteristics of the floor. Accordingly, this study analyzed the impacts of dynamic load disturbance induced by roof breaking on the failure depth of the stope floor. The constructed model was employed to investigate the floor failure depth of mining face 8031 within a coal mine in Feicheng, Shandong Province using numerical simulations and in-situ water injection tests in boreholes. Results and ConclusionsThe results indicate that the dynamic loads induced by roof breaking were superimposed with the static load stress in the floor produced by the support pressure of the stope, leading to intense disturbances to the stress concentration and unloading zones of the floor. The degree and range of the stress field concentration on the floor increased significantly during dynamic loading. The dynamic load disturbance induced by roof breaking further intensified the failure of strata in the stope floor. The theoretical calculation, simulation analysis, and field measurement results revealed similar depths of 5.9, 6.6, and 6.3 m for the secondary floor failure caused by initial weighting-induced dynamic load disturbance， verifying the accuracy of the theoretical model. The results can reflect the laws of the time and locations of water inrushes on the floor， providing a significant theoretical basis and reference for the prevention and control of water inrushes from deep floors.