Research on subsidence law of overlying strata in full mining of extra-thick coal seam

The problem of strong mine pressure during the mining of the near goaf working face in Datong coalfield is more serious than that of the first mining face. In order to study the overlying strata movement law under the full mining conditions of extra-thick coal seam, the overlying strata movement of 8202 working face in Tongxin Coal Mine is monitored and analyzed by using a wireless remote monitoring system for internal strata movement of overlying strata under mining condition and borehole TV observing technology. The results show that in the early stage of large space mining of extra-thick coal seam, the overlying strata will be deformed and damaged from top to bottom in the advance working face, and then the layer group will break down and move normally from bottom to top. The overlying strata deformation and destruction in the mining site shows the change characteristics of stage step-up jump, which has a consistent correspondence with the location of the key strata, indicating that the key strata play the main control role in the strata movement. Under the condition of full mining, the overlying strata movement appears linkage subsidence phenomenon. Through physical simulation experiments, this paper further studies the nature of the whole-strata linkage subsidence of the overlying strata during full mining. The results show that before the initial breaking of the main key stratum, the grouped layered movement trend of each key layer is more obvious. After the main key stratum breaks for the first time, affected by the periodic breaking length of each key stratum and the compound breaking law of the upper and lower rock layers, the overlying strata subsidence and movement is more likely to show the whole-stratum linkage phenomenon.