Comprehensive study on the deformation and failure characteristics of a mining-impacted deep double-longwall working face floor

The key solution to the safe mining of coal over a deep confined aquifer is to obtain and understand the deformation and failure characteristics of the working face's floor strata. In this work, we took a typical fully mechanized mining deep double-longwall working face floor of Chengjiao Coal Mine as a study case. Through in situ tests we established a three-range partition model for mining-induced underground pressure propagation in the coalbed floor to reveal the behavior of pressure propagation in both the vertical and horizontal directions of the floor strata. We found that the floor experienced consecutively three quantitative deformation ranges, and showed three different underground pressure behavior ranges; the measured failure depth in the mining-induced double-longwall working faces floor was less than 27 m. In addition, the groups of rock mass were divided for mining the coal roof and floor, and we constructed a 3D engineering geological numerical model for the double-longwall working faces, and numerically simulated the plastic zone distribution features and the maximum vertical stress at different floor depths, finding that there were three stages for vertical stress along the mining coalbed floor depth. We also found that the failure depth of the floor was not more than 27 m by numerical simulation, consistent with the in situ measured result. All these results are of significance for the prevention and control of water inrush out of the double-longwall working face floor and for the support of their related roadways. (paper)