Square-form structure failure model of mining-affected hard rock strata: theoretical derivation, application and verification

The coal-bearing strata consist of rock and coal strata with diverse thickness or mechanical strength, and thus they, especially the thick–hard rock strata, are distinguishing in movement and failure laws during coal mining. The failure of the thick–hard rock strata may affect the strata stability and cause serious coupled dynamic hazards and environmental problems. In the paper, the failure model of thick–hard rock strata was derived theoretically, which was applied to calculate the failure laws of the thick–hard igneous sill, and then, the model was verified by the methods of numerical simulations and surface subsidence measurements. The results indicate that: (1) the failure laws of the hard roof strata were analyzed based on the four-edge-clamped thin-plate assumption, and thus, the square-form structure failure of the hard roof stratum, which case is defined as the SSF model, occurs most possibly with the square gob for larger normal stress components; (2) the SSF model was applied to calculate the failure laws of the thick–hard igneous sill, and it would be broken with the approximate square-form gob of 310 m long and 350 m wide in Yangliu Coal Mine, Huaibei Coalfield, China; and (3) both the simulation results and the surface subsidence measurements indicate that the initial failure length of the thick–hard igneous sill was about 320 m with the square-form gob, verifying the correctness of the SSF model. The results could provide the theoretical guide for mining rock strata control and dynamic hazards prevention.