A Numerical Simulation About The Low Of Overburden Strata Breakage And Movement When Shallow Coal Seam Being Mined

Yulin Shenfu area of northern Shanxi region contains a large number of high quality coal resources,shallow deep, thin bedrock (typically thickness less than50m), overlying thick loose aeolian sand aquifer is the typical characteristic of the mine being mined in this area.Currently,the overburden is damaged seriously in the process of mining,which causes the loss of water in the aquifer, In order to provide some theoretical guidance to water-preserved mining, this article studied by UDEC the low of breakage and movement of overburden strata when shallow seams is mined in different mining height and different depth, and studied by FLAC3D the low of breakage and movement of overburden strata when shallow seams is mined in different face length. Through the researches, I get the following conclusions:(1)With work face advancing, the distance of overburden strata’s maximal stress advancing into the coal wall changes periodically, from which we can infer that the distribution of stress in advance is affected by periodic roof pressure. To be specific, while work face is advancing, only when the roof is broken because of periodic pressure, the stress in advance will redistribute. On the contrary, when periodic roof pressure does not happen, stress in advance will not redistribute when work face is advancing.(2)The higher the mining height is, the larger the maximum of stress in front of face is; the higher the mining height is, the larger the maximum of overburden strata’s vertical displacement is; the higher the mining height is, the higher of the maximum height of fissure development. Therefore, it is possible to control the fracture height and quantity to some extent by reducing mining height.(3)When models with different depth are mined, the relationship between stress concentration factor of overburden rock in front of the coal wall and buried depth is as followings, When the overburden rock is relatively close to the coal seam, the factor generally decreases with the increasing of buried depth, but When the overburden rock is far from the coal seam, the influence of buried depth to the factor becomes slightly. The relationship between fissure development and buried depth is as followings, the deeper the seam is buried, the higher of the maximum height of fissure development is, and the wilder distribution of fissure is. However, if when the depth is decreasing, the thickness of the impermeable layer also reduce the same thickness, flood risk will increase.(4) when the length of work face increasing, the concentrated stress in front of the coal wall in the central of work face is significantly increasing, but, on both ends of work face,where near the roadway, the concentrated stress is just increasing slightly. Under the same advancing distance, the longer the work face is, the larger the area of roof hanging open, the greater the stress concentration around the goaf formes, the greater the subsidence of strata above goaf is, and the wider the distribution of damaged overburden rock by mining is.Therefore, it is desirable to reduce the destruction of overburden rock by reduce the length of the work face.