Study on influence of key strata on surface subsidence law offully-mechanized caving mining in extra-thick coal seam

The thickness of one-time mining and coal seam produced in the fully-mechanized caving in extra-thick coal seam is large and the height of caving zone and fracture zone increase correspondingly so that the development of the "two zones" directly affects the upper part of the overburden and the thick and hard strata that plays an important role in controlling surface subsidence. The movement and deformation of key strata which plays a role in controlling subsidence is closely related to the surface subsidence law. In order to explore the influence of key strata on the control of surface subsidence of extra-thick coal seam using fully-mechanized top coal caving method from the perspective of rock movement and deformation inside the overburden rock, Engineering Analogy and Numerical Simulation Method were applied to determine the height development of the "two zones" for the No.914 working face of Dongpo Mine. In this case, key strata theory was used to calculate the fracture spacing and position of each sub-key strata and key strata. The 3DEC Simulation was used to study the influence of key strata on the surface subsidence law. The results show that the application engineering analogy method combined with the numerical simulation plastic zoning method can comprehensively determine the high development of the "two zones". The movement and deformation of the overlying strata and surface is controlled by the thick and hard rock strata, which is characterized by the combination of the overburden strata fracture characteristics. The shorter the fracture length of rock beam in key strata, the gentler the edge of the subsidence basin and the larger the influence range of the subsidence basin. Due to the difference of the fracture spacing and form in key strata, the open-off cut side of the subsidence basin is steep and the stopping line side is relatively gentle.