Study On The Influence Of Coal Pillar On The Protected Area Under The Steep Dip Protective Seam Mining In Donglin Coal Mine

In order to study the influence of coal pillar deformation on the protection scope of protected layer,taking Donglin coal mine protection layer mining as the engineering background.Based on the theory of elastic-plastic damage and deformation and the theory of rock mechanics.The methods of field sampling,laboratory test,physical analogue simulation,numerical calculation and field investigation are adopted.The influence of the protective coal layer in the protective layer on the suffer protection area of the protected layer is studied.The main results are as follows:(1)Through on-site sampling,processing into standard test pieces in the laboratory,performing uniaxial compression,brazilian splitting and compression shear testing.The uniaxial compressive strength,elastic modulus,Poisson’s ratio parameters,tensile strength,and the cohesion and internal friction angle of the test specimens in different strata were obtained.It provides important physical and mechanical parameter basis for physical similarity simulation test and numerical simulation calculation.(2)To determine the physical and mechanical parameters of similar materials in physical similarity simulation tests.The susceptibility to uniaxial compressive strength,elastic modulus and Poisson’s ratio of similar materials was studied by three factors,namely the ratio of sand and cement of similar materials,density and residual water content.The results show that the ratio of sand and cement,density and residual water content have interaction effects on the uniaxial compressive strength of similar materials,but there is no interaction effect on Poisson’s ratio,and the ratio of sand and cement and density have interaction effects on elastic modulus.The regression equations of the uniaxial compressive strength,elastic modulus,Poisson’s ratio,sand-binder ratio,density and residual water content of similar materials were obtained.(3)Physical similarity simulation test research shows that after the mining of the upper and lower sections,the swelling deformation curve of the protected layer containing the isolated coal pillar is approximately "M".In the upper section,the expansion deformation value of the protected layer corresponding to the lower section is higher than that in the lower section,but the minimum expansion deformation value at the middle of the "M" curve in the expansion deformation is also above the 3 per thousand line.This indicates that the danger of coal and gas outburst has been eliminated in the area,and the unprotected area of the section coal pillar has not been generated in the protected layer.(4)Based on the multi physical field coupling theory of coal seam gas flow,the numerical simulation of the influence of the inclined length of the coal pillar in the protective layer on the deformation and the residual gas pressure in the protected layer is carried out.The results show that the smaller the length of the coal pillar is,the larger the displacement and deformation of the protective layer will be.The optimum width of the section coal pillar is 10 m,and the pressure relief curve of the upper coal pillar is similar to "M",which is based on the pressure relief deformation criterion 3 per thousand and the protection layer is 150 m.(5)After the mining of the Donglin coal mine,the remaining gas pressure,the residual gas content and the caving of the pillar of the protected layer were investigated in accordance with the provisions of the anti outburst regulation.The results show that the residual gas pressure in the protected layer is less than 0.74 MPa and the residual gas content is less than 8m3/t.The coal pillar in the section of the protection layer has collapsed under the action of concentrated stress and gravity.Only the remaining thin coal lines are attached to the top and bottom of the coal seam.