Study On Movement Laws Of Overlying Strata And Surface Deformation Of Extra-thick Coal Seam Mining

In the northwest of China, the distribution of thick coal seams is wide, and the regularity of overlying strata movement and surface subsidence after coal seam mining have great differences compared with that of general coal seam.The paper aimed at the special geological conditions, such as largethickness of the coal seam in Ordos region, the surface is covered by loess layer, combined with the surface subsidenceafter mining the typical working face,combinedwith field survey, theoretical analysis, similar material test and numerical simulation methods, studied overlying strata movement and surface subsidence features after thick coal seam mining.The main achievements of the paper are as follows:(1) According to overlying strata structure of Buliangou, based on the key strata theory and criterion of key layer,two layers of key strata of overburden were determined, the first layer is gritstone and it is sub critical layer, the second layer iscombination of sandy mudstone and gritstone and it is first key layer, their initial and periodic breaking distance and the fractured formand instabilitywere analyzed.(2) Analysis of thick coal seam mining, ―high level short cantilever beam-stepped rock beam‖ of roof strata after mining was established, and based on the previous studies, support force of high step rock beam was corrected.(3) There exist only two belts include caving zone and fractured zone in overlying strataafter thick coal seam mining; through the site observation, numerical simulation and similar material simulation, we get the key layer has a of crack zone development and surface subsidence control. After mining in working facecontrol action on both fracture zone development and subsidence, both sides of the working face and the side of open-off cut, cracks are obvious along the caving angle after overlying stratafracture.