The Analysis of Seam Pressure Released Effect in Protection Layer Mining of Kilometer Deep Shaft

The vertical depth of Ji₁₅-31010 working face in the twelfth mine of Pingdingshan Tian'an Coal Industry Co.Ltd is 1 015 m to 1 130 m,and it is coal and gas outburst seam.Pre-drainage gas by mining liberated seam Ji₁₄ is the key technology to solve the coal and gas outburst of Ji₁₅ seam.Therefore,the pressure released effect of the lower coal seam in the deep protection layer mining should be further researched.Firstly,the three-dimensional numerical model is established according to the actual geological conditions and the stress distribution of the lower Ji₁₅ coal seam during Ji₁₄ seam mining is calculated.The calculation result showed that the pressure in the lower Ji₁₅ coal seam first increased and then decreased during upper protection layer mining.Coal seam pressure was reduced to less than 1 MPa after the mining face passed 40 m,while the maximum stress values was up to 42 MPa in the stress-concentrated areas outside of the gob.Field monitoring data showed that gas concentration increased significantly in the seam roadway under the gob,while the gas concentration changed less in outside of the seam roadway;roadway deformation tended towards stability and coal seam was got the fully pressure relief after the mining face passed 40 m.The numerical results and on-site monitoring data showed that deep close protection layer mining can significantly reduce the pressure of the lower part of the coal seam and release the coal seam gas.However,due to the influence of concentrated stress,it is difficult to release the lower coal seam gas at the edge of the gob.