Research On The Overlying Rock And Surface Movement Law Of Gently Inclined Coal Seam Mining Under Thick Loose Layer And Thin Bedrock

In coal mining activities,when the geological conditions are thick loose layer and thin bedrock,there are certain differences between the surface movement and deformation laws caused by coal mining and those under general geological conditions.At present,the research in this area mainly focuses on the strike of horizontal coal seam or inclined coal seam.In order to further study the particularity of the tendency of gently inclined coal seam under thick loose layer and thin bedrock and the law of surface movement and deformation,this paper takes the1201 working face in the West Second mining area of Linsheng Coal Mine as the engineering background,and carries out the research by combining the methods of physical and mechanical parameter test,similar material simulation test,numerical simulation analysis,theoretical analysis and comparative verification.The main research contents and results of this paper are as follows:(1)The natural density,tensile strength,uniaxial compressive strength,elastic modulus E,Poisson’s ratio,cohesion c and internal friction angle of mudstone,sandstone and coal in the roof of the working face were obtained by carrying out indoor density test,splitting test,uniaxial compression test and conventional triaxial compression test.The test stress-strain curves of corresponding samples were obtained by sorting out and analyzing the test data of coal and rock mass,and the variation law of the curves was described.(2)Through the physical similarity simulation test,the movement,deformation and failure characteristics of the upper bedrock of the gently inclined coal mining face under the thick loose layer and thin bedrock are revealed.The test results show that when there is only one key layer in the thin bedrock,the control effect of the key layer on the movement and deformation of the rock is more obvious.Strong energy fluctuation occurs at the initial fracture of the thick direct roof in the thin bedrock,which can be regarded as the initial pressure of the working face in combination with the definition of the initial pressure of the working face and the calculation of the fracture energy of the roof.(3)Through the physical similarity simulation test,compared with the mining related research and analysis of shallow buried gently inclined coal seam under general geological conditions,it is found that the difference of strata ’cross fall angle between the upper and lower mountains of the overlying rock after the fracture of the inner roof of the thick loose bed and thin bedrock is relatively small,and the initial weighting step of the basic roof is large.With the advance of the working face,it is difficult to form an effective "masonry beam" support structure in the thin bedrock.After the mining of the working face,the collapse zone in the thin bedrock forms an irregular "trapezoid",showing asymmetry up and down the mountain.(4)Through the design of different loose layer thickness,direct top thickness and key layer thickness numerical model scheme,the influence of different variables on surface movement and deformation law is studied.It is found that the maximum subsidence value and subsidence coefficient increase gradually with the increase of loose layer thickness;The maximum surface subsidence value and subsidence coefficient gradually decrease with the increase of the thickness of the key layer and the thickness of the direct top.It can be seen that the change of the maximum surface subsidence value caused by the change of the thickness of the bedrock and the loose layer is opposite.(5)Through the curve fitting analysis of the numerical simulation results,the fitting formulas of loose layer thickness,key layer thickness and direct top thickness with the maximum subsidence value and subsidence coefficient of the surface are obtained.By comparing the thickness changes of the loose layer and the bedrock,it can be seen that the thick loose layer has a dual effect on the thin bedrock.First,it acts as a load on the thin bedrock,making it difficult for the thin bedrock to form an effective support.Second,it buffers the impact of strong weighting on the surface when the roof of the thin bedrock breaks.(6)Combined with the key layer theory and the movement and deformation difference between thick loose layer and thin bedrock,the bedrock subsidence model is coupled with the loose layer probability integral subsidence model by using the random medium theory,and the prediction mathematical model of surface subsidence before and after the fracture of the key layer is established.Compared with the measured data curve,it is found that the fitting degree of the prediction curve is high.The paper has 61 figures,16 tables and 85 references.