Study On The Load Transfer Mechanism Of Overlying Coal Pillars Mined Out Of Shallow Buried Coal Seam Group

The shallow buried coal seam group in the Shendong mining area is subject to the constraints of coal mining process and method in the early stage of mining,some coal pillars will be left behind,which leads to the lively mine pressure easily occurring at the overlying concentrated coal pillars when the working face of the lower coal seam advances to them.A lot of research has been done on the structural instability of a single key layer between coal seam groups,but less research has been done for the conditions of multiple key layers between seams,especially on the evolution of overburden mining fissures and stress transfer during the coal pillar mining stage when the spacing between seams is large and the number of key layers is many.In this paper,we use numerical simulation,physical simulation and field measurement to study the overburden breakage characteristics and support stress at the coal pillar stage,and develop corresponding prevention and control measures for the mine pressure disaster at the coal pillar of the working face.The main research results are as follows.(1)The numerical simulation and physical simulation results show that the subcritical layer 2 between the coal seam group layers is affected by the overlying excessive load,and the damage fracture occurs first at the boundary of the coal exit column,and sub-critical layer 2 further transfers the load to sub-critical layer 1 during the rotary deformation process,which makes sub-critical layer 1 break and destabilize,resulting in the overall cut-down motion of the overlying rock between the layers,thus indicating that the breaking sequence of the critical layers when the coal seam group layers are widely spaced and load transfer are from top to bottom.(2)Under the condition of multi-layered key layers between coal seams,when the working face of the lower coal seam pushes out the boundary of the overlying coal pillar,the peak over-supporting stress is 12.45 MPa,and the overlying rock between the seams is cut down as a whole under the high stress,and the maximum sinking of the roof is 1.97 m.After analyzing the influence of the mining height and the size of the layer spacing on the appearance of mine pressure at the stage of the coal pillar,it is considered that the appearance of mine pressure at the working face is more moderate only when the ratio of the layer spacing to the mining height is greater than 16.75 times.The maximum sinkage of the roof plate is 0.4m,which is almost unaffected by the mine pressure and can effectively prevent the occurrence of strong mine pressure at the coal pillar boundary.(3)The prevention and control measures of the strong mine pressure disaster of the overlying coal pillar are proposed,and the blasting treatment of the coal pillar makes the high stress on the pillar transferred to the gangue and the surrounding rock layer,so that the safe production of the working face can be guaranteed.Numerical simulation analyzes the overburden sinking displacement and peak support stress before and after blasting and compares the analysis,evaluates the specific control effect,and combines with the mining practice to show that the weakening treatment of coal pillars can effectively guarantee the safe and efficient production of the working face.There are 62 figures,9 tables and 95 references in this paper.