Research on Development Characteristics of Overburden Fracture in Lower Protective Layer Mining of High-Gas Coal Seams
The development height of fractured zone is the key factor to judge the mining feasibility of the lower protective layer.Taking No.8 coal seam and No.7 coal seam in Tongting Coal Mine as the engineering research background,the development characteristics of fractured zone in No.8 coal seam after mining were analyzed by theoretical calculation,numerical simulation and distributed optical fiber observation method.The empirical formula of"three zone discrimination method"was used to calculate that the No.7 coal seam was located at the lower edge of the fracture zone formed after the mining of the No.8 coal seam.In theory,the lower protective layer of the No.8 coal seam can be mined.UDEC was used to construct a numerical model for the rock strata of the No.8 coal seam working face,the numerical simulation shows that the height of the caving zone is 14.6 m,and the height of the fracture zone is 51.6 m,which is highly consistent with the theoretical calculation,and further verifies the feasibility of the lower protective layer mining.The measured strain data of distributed optical fiber are processed,and the height of the fracture zone is stable at 53.4 m,which is consistent with the height of the fracture zone obtained by theoretical calculation and model simulation.Combined with the three methods of"three zones"formula calculation,numerical simulation and distributed optical fiber monitoring,the development height of fracture zone after the mining of No.8 coal seam is about 50 m,which is greater than the coal seam spacing between No.7 coal seam and No.8 coal seam.It is proved that the mining of lower protective layer is feasible,and the study can provide a reliable theoretical basis for the safe mining of later mining area and working face.
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