Study On The Failure Mechanism Of Overburden And The Law Of Surface Subsidence In Full Pillar Mining With Wide Strip

Wide strip full pillar mining is developed based on the theory of wide strip mining and combined with the characteristics of full pillar mining,It is an important measure to liberate "three under" coal and has been applied in recent years.On the basis of the present situation of the whole pillar mining with wide strip,combined with the mechanical analysis,the theoretical analysis of the horizontal deformation of the surface,3DEC numerical simulation,the simulation of the similar material test and the actual measurement research,this paper makes an in-depth study on the theoretical basis,the realization principle and the applicable conditions of the full pillar mining with wide strip,makes a theoretical and Simulation Study on the failure characteristics of the overburden in each stage of the full pillar mining with wide strip,and studies on the optimization of the mining sequence of the coal pillar working face.The above research has theoretical and practical significance in promoting the application and development of the theory and technology of wide strip full pillar mining,better emancipating the "three under" coal and improving the recovery rate of coal resources.The main research achievements of this paper include the following aspects:(1)The space-time theory of strata movement,such as the spatial distribution of overburden affected by mining,the change rule of corresponding surface subsidence and horizontal deformation,the time rule of mining influence,and the characteristics of mining additional stress releasing with time,are studied.On the basis of the above,the horizontal deformation characteristics of different stages in the mining process of wide strip full pillar are analyzed,which lays a foundation for the realization of wide strip full pillar mining The theoretical basis is established.(2)This paper analyzes the main influencing factors of the applicable conditions of wide strip full pillar mining under certain geological mining conditions,and concludes that subsidence and dynamic horizontal tensile deformation are two key factors,and deduces the relationship between the applicable conditions of wide strip full pillar mining in near horizontal coal seam and(gently)inclined coal seam.(3)According to the failure characteristics of overburden,the change law of roof structure in the mining process of coal pillar working face is analyzed,the mechanical model of roof structure before mining of strip coal pillar working face is established,and the calculation formula of its first breaking distance is deduced.On this basis,the viewpoint that the surface subsidence of full pillar mining with wide strip is less thanthe sequential mining of working face due to the uneven size of broken rock block is put forward.Through the analysis of the measured data and numerical simulation results,the results are consistent.(4)According to 3DEC numerical simulation,the failure mode of overlying rock of upper and lower mining boundary in wide strip full pillar mining under(gently)inclined coal seam is analyzed.The rotary bending and sinking of rock stratum at the lower mining boundary is obvious,mainly shear failure.The fracture angle of rock stratum gradually decreases with the increase of coal seam dip angle,and the decreasing range gradually increases;the tensile failure of rock stratum at the upper mining boundary is mainly,The fracture angle increases with the increase of coal seam dip angle.The expression of the relationship between the fault angle and the coal seam dip is obtained.(5)Through theoretical analysis,when all coal pillars cannot be mined at the same time in the full pillar mining stage,in order to better control the influence of static deformation on buildings,the optimization criteria of mining sequence of coal pillar working face is proposed,which provides a theoretical basis for the popularization and application of wide strip full pillar mining technology.(6)It can be seen from the results of actual measurement,numerical simulation and similar material simulation test that,according to the analysis of surface subsidence,the subsidence coefficient is still small after mining one coal pillar working face,the analysis of the ground deformation is verified by the measured results.And it can be seen from the side that the periodic static deformation of the surface formed after mining one coal pillar working face is also small,and some of the static deformation occurs within the scope of the surface protected body.According to the surface deformation after the completion of full pillar mining with wide strip,combined with the mining sequence optimization criteria of coal pillar working face,the wide strip and full pillar mining can be popularized and applied.