Research And Analysis On The Effect Of Deformation And Pressure Relief Of Mining Rock Mass By Protective Layer On Thick Hard Roof

Protective seam mining is one of the effective methods of gas pressure relief treatment in deep mining.With the development and utilization of coal resources extending to the deep,the mining disturbance behavior has a great impact on the mechanical state and seepage field of deep coal and rock mass.Therefore,the paper aims at the problems that the thick hard roof of No.9 coal seam in Huainan Zhangji coal mine is difficult to caving,the pressure relief gas of No.8 coal seam is large,and the sandstone gas control of No.9 coal seam roof is difficult.Using the comprehensive methods of theoretical analysis,similarity test,numerical simulation and engineering practice,the double pressure relief effect and research of thick and hard roof cutting and upper protective layer mining have been carried out,and obvious technical and economic benefits have been achieved.The main conclusions are as follows:(1)The similar simulation experiment is used to analyze the mining instability characteristics and fracture evolution law of the overburden in the stope and study the macro deformation and expansion law of the underlying coal and rock mass.In the process of overburden collapse,the angle of fracture convergence is distributed in 50 ～70 °,and the collapse area is characterized by "positive trapezoid".The effective expansion area of the underlying coal seam is 47 m from the coal wall to the rear.(2)The numerical simulation software is used to study the influence of roof presplitting blasting on the bearing pressure distribution of the underlying coal seam and analyze the stress field distribution of the protected seam under different advancing distance.After the roof is weakened,the peak value of the advance bearing pressure shifts forward,forming a large stress concentration area in the front section without roof cutting,which basically has no impact on the expansion distribution law of the underlying coal seam,and the pressure relief area is basically the same as that before roof cutting.However,in terms of the overall pressure relief effect,the roof cutting weakening treatment increases the fracture development of the rock stratum to a certain extent and improves the expansion deformation of the protected seam.(3)The mechanical model of pressure relief protection of upper protective layer mining to underlying coal and rock mass is constructed.The expansion rate distribution equation and effective pressure relief range of the underlying coal seam are derived,and the main controlling factors affecting the pressure relief effect of the underlying coal seam are revealed.(4)Thick and hard roof leads to frame pressing accident,and large-area collapse leads to gas overrun,so it is necessary to precrack the roof.According to the properties of roof strata,stress distribution,fracture evolution law of surrounding rock and relevant parameters and laws of gas migration in fully mechanized mining face.According to the geological conditions of the mining area,the layout of "fan-shaped" blasting holes is proposed for segmented blasting,and the specific parameters of blasting holes at different positions are given.(5)Combined with the field observation data,the roof pressure characteristics of the working face are analyzed,including the resistance observation of the hydraulic support,the roof breaking step and the ground pressure behavior law.It is concluded that the stope support can meet the control requirements of the roof during normal mining.(6)The continuous mining of the upper protective layer provides a good gas drainage and pressure relief area for the high gas bearing coal seam.The weakening of the roof of the protective layer further improves the crack development and penetration of the roof of the rock stratum,forming a gas flow channel,which is conducive to the drainage of pressure relief gas.The amount of gas mixed extraction is affected by the advancing distance of the working face,the distribution of mining stress and the self expansion deformation of coal and rock mass.On the whole,the presplitting blasting and periodic breaking of the roof improve the fracture development and penetration of the rock stratum and improve the drainage amount of pressure relief gas.Figure 69 Table 12 Reference 91...