Mining-induced displacement deformation law in full-columnar overburden and its design guidance in gas extraction

A certain degree of displacement deformation would occur in the overburden after the coal seam is mined. In this case, it is of great importance to master the displacement deformation law of each key stratum (KS) in the overburden. With a working face as the research object, this study explored the displacement deformation law of each key stratum in full -columnar overburden by comprehensive methods of mechanical test, 3DEC numerical simulation, similar material physical experiment etc. Firstly, the full -columnar overburden was drilled for core and then processed with mechanical test to obtain the actual mechanical parameters of main strata. Based on the actual mechanical parameters, a full -columnar 3DEC numerical model was established. The simulation reveals that the displacement deformation below the third key stratum (KS3) is large and obvious separation layers occur in the region. In contrast, synchronous bending subsidence is formed from the fourth key stratum (KS4) to the ground surface with no obvious development of separation layer. In addition, the similar material physical experiment was also carried out, which reveals that fractures are formed below KS3, and in contrast, only bending subsidence is formed in KS4 and above strata. The results of physical experiment are basically consistent with numerical simulation. As are revealed, the development height of separation layers are only below KS3 (nearly 60 m above the coal seam), and the displacement curves of the broken key strata are W-shaped and those of the bended strata are U-shaped. On this basis, the specific range of O -shaped circle fracture zone(the width is 100 m) are obtained through the inversion of mining -induced fracture characteristics. The results are of great guiding significance for the drilling arrangement in gas extraction.