Deformation Mechanism And Its Characteristic Of The Surface And Overburden Due To High-Intensity Coal Mining Under Wind-Deposited Sand Zone

Shenfudongsheng mining area,where the surface is covered with the thick wind-deposited sand,is located in boundary intersection of Shaanxi and Inner Mongolia province.There is abundant coal resource with thick coal seam,shallow buried,thin bedrock and simple geological conditions as well.Currently,a kind of underground mining mode with high-intensity and efficiency are formed and widely used here.However,along with the high-intensity mining in this wind-deposited sand zone,a lot of damages such as severe damaged in overburden,movement and intense deformation of the ground are appeared,which shows a unique rule and should give a widely attention.Therefore,the study focuses on these two aspects.In aspect of the surface deformation,based on geological and mining conditions in Shenfudongsheng mining area,the angle quantity parameters(dynamic and static)and its predictive parameters of the surface movement and deformation caused by high-intensity mining in the wind-deposited sand zone were obtained,through the analysis of data of the surface movement and deformation.And the reasons and characteristics of each parameter were analyzed.From relations of the surface deformation and movement and its deformation rates,the whole process of dynamic deformation of the surface by high-intensity mining was study and the rules of discontinuous deformation were summarized.The surface cracks always show "strip" forms,which occurs in a certain distance,in the front of working face.Between each of two "strip" cracks,there are a number of small cracks.While after working face advanced,the cracks showed a phenomenon of gradual closure by the action of stree compression and wind-deposited sand,which reveals the unique rules of the surface deformation under the high-intensity mining and thick wind-deposited sand conditions.The relations between the width of the surface crack and its periodic rock pressure were discovered.In aspect of overburden destruction,a "two strips" destruction form was found existing in overburden under the conditions of high-intensity mining,shallow buried in wind-deposited sand zone.New formula that match with high-intensity mining for calculating caving zone and water flowing fractured zone were built,as well as theactual height of "two strips" which conform to high-intensity mining were obtained.By using numerical simulation method,the stress variations of overlying strata caused by mining were analyzed,the stress distributions of overburden caused by high-intensity mining in wind-deposited sand zone were studied,and evolution process of overburden by mining which from elastic zone to plastic zone were discovered.Through simulated experiment with similar materials,the relations between overburden deformation and the surface deformation were analyzed.The height of upgrowth of caving zone and water flowing fractured zone of overlburden were obtained.Based on the critical layer theory,structures of overburden and its breaking mechanism were discovered,and the cases analyses were done as well.The study obtained can be used as useful references and guidelines for establishing policies for safety and efficiency coal mining in thick coal seam,shallow buried and thick wind-deposited sand zone.