Numerical investigation of mining-induced strata disturbances using a discontinuous deformation and displacement coupling method

Strata movement and ground subsidence caused by mining have a significant influence on the safety and stability of the goaf. By taking the mesoscopic heterogeneity of rock masses into account, the discontinuous deformation and displacement (DDD) method was applied to simulate the whole failure process of overlying strata after coal mining under different advancing distances of the working face. The results show that key strata would not be broken when the working face was advanced by 30 m. When the advancing distance increased to 50 m, the first key stratum was broken; when it went up to 70 m, both the first and the second key strata were broken and collapsed successively. Moreover, the bed separation of strata had become particularly obvious and a three-zone phenomenon—including collapsed zone, fractured zone, and continuous deformation zone—presented throughout the whole rock mass when the distance rose to 90 m. As the working face is advanced by increasing distances, there are increases in the ranges of deformation, disturbance, and damage in the overlying strata, as well as surface settlement. Meanwhile, the gradual collapse process of the strata is further analyzed in terms of the background-stress evolution; i.e., stress accumulation, stress shadow, and stress transference. Furthermore, it has been proven that the DDD method is an effective approach to reproduce the whole process of strata collapse and macro instability from small deformation, crack initiation, and propagation to block translation, rotation, and contact, which is crucial for predicting strata movement and surface subsidence.