Research On Law Of Thin Bedrock Shallow Buried And Thick Soil Layer Top-coal Caving Mining Overlying Strata Migration

Caving mining technology, lacking of theory support and practice, rarely used in thenorth of Shanxi, was first used in Ma-huang-liang coal mine of Yulin Yuyang area in the northof Shanxi, and was used to carry out the9m shallow buried coal seam caving mining practiceunder the thick soil layer thin bedrock geological conditions.Using combining method oftheory analysis, similar material simulation, numerical simulation and field observation,aiming at particular occurrence situation of shallow buried depth, thin bedrock and thick soil,adopting the caving mining technology, the research on covered strata broken migration lawand working face mine pressure behavior were conducted.the conclusions were as following:(1)"Three zones" distribution law, during full-mechanized caving mining process, the"two belts" is obviously shown in the overlying rock strata, that are caving zone (26metershigh) and fissure zone (170meters high), which had been through to the earth surface.(2) Bedrock migration fracture rule: during caving mining process, without layerstructure in thin bedrock, under the overlying thick soil layer load, the thin bedrock layer iseasy to rupture and lost stability, and the whole lost stability weight most immediately effectson the bracket, immediate roof first caving pace is38~40meters, basic roof first caving paceis54~60meters, periodic caving span is16~22meters.(3) Thick soil layer migration fracture rule: with the development of mining，thick soillayer bend gets separated fissures, fracture soil layer tends to transfer bond formation withsoil before and after the end of the matrix, and forms a certain "arch" structure, the "arch"structure will experience periodical change of Lost stability-Balance-Lost stabilityagain.Meanwhile, after fissure extending to the loess layer, the ahead of big fissure will arisein front of coal wall20~25meters, with the working face advancing, the ahead of big fissurewill arise constantly, when the working face advances to4~5meters away from the fracture,intense strata behaviors will easily turn up. And the reason for intense strata behaviors is theappearance of ahead of big fissures and which arise rapidly extending to the surface, while the working face continues to advance.（4）Law of ground subsidence: maximum ground subsidence of6~7m,caving angle ofrock strata of70°~77°, and above the working face along the inclined direction amount oflarge tensile cracks appear every15~30meters, maximum crack width of0.8meters.