Self-forming roadway of roof cutting and surrounding rock control technology under thick and hard basic roof

Roof presplitting is the key to the non-pillar mining technology with automatically formed roadway, and its effect is directly related to the stability of gob-side entry retaining.Under the condition of thick and hard basic roof, the underground pressure phenomenon, the law of overlying strata migration and the control technology of gob-side entry retaining by roof cutting have their particularities.Based on the engineering background of gob-side entry retaining by roof cutting in a coal mine, through the UDEC numerical simulation, physical similarity simulation, theoretical analysis, and on-site industrialization test, the research on the technology of cutting roof and pressure relief and surrounding rock control technology under the condition of thick and hard basic roof is carried out.Firstly, by using the UDEC numerical simulation software to compare and analyze the stress and displacement distribution law of the surrounding rock of the retained roadway under different roof cutting heights.The numerical simulation results show that when roof cutting height is 7 m, the roof on the goaf side cannot be broken along the roof cutting line, which causes the roadway roof to sink and separate.When the roof cutting height is 9 m, the basic roof collapses along the cutting seam line, and the basic roof internal stress above the coal wall decreases from 25-30 MPa to 20-25 MPa.When the cutting roof height increases again, it has little effect on the stress distribution.Secondly, the laws of overlying strata migration and mine pressure changes under different cutting heights are compared and analyzed by physical similar simulation experiment.The results show that when the roof cutting height is 7 m, the basic roof fracture line is located on the solid coal side, and the surrounding rock of the roadway will be squeezed and destroyed by the fractured rock block, which lead to the roadway roof to be broken, separated, tilted, or even large area collapse of immediate roof and basic roof.When the roof cutting height is 9 m, the basic roof is broken along the cutting seam line, and the roof collapses in the goaf makes no extrusion effect on the surrounding rock of the roadway, which provides an efficient pressure relief effect.As the cutting roof height increases again, when the roof cutting height is 12 m, the basic roof breaks along the cutting seam line, while the pressure relief effect changes little.Thirdly, through theoretical analysis and calculation, the key parameters of the roof presplitting required by the field industrial test are determined.The industrial test results show that for thick and hard roof, the explosive charge of hole bottom has a significant effect on blasting effect.When the explosive charge amount is 1.0 kg/m, the resistance of hole bottom can be overcome, and a good roof presplitting effect can be achieved.When the roof cutting height is 7 m, the upper part of the single hydraulic prop in the test section of the roadway is compressed and bent, and the lower part falls into the floor.The roadway roof is inclined to the goaf side, and the subsidence of the roof on the side of the cut seam is about 450-500 mm.When the roof cutting heights are 9 and 12 m, the subsidence of the roof at the side of the cut seam in the test section is small, and no single hydraulic prop damage is found, so the roof cutting effect is notable.Finally, based on the above study, taking into account the site geological conditions, technical and economic considerations, the specific technical scheme of roof cutting pressure relief is determined.The strong support system of the gob-side entry retaining, which integrates "reinforcement support of high-strength roof cutting anchor cable, blasting presplitting and pressure relief, single column strong support, and anti-instability shrinkable U-shaped steel with top-bottom inserted, retaining gangue with mesh", is put forward in this paper.The result shows that the final deformation of roof and entity coal side is 186 and 119 mm respectively, ensuring the safe use of the next working face. © 2021, Editorial Office of Journal of China Coal Society. All right reserved.