Overlying Strata Movement Law And Gas Drainage Design In Fully Mechanized Top Coal Caving Face Of Zhujiao Coal Mine

High gas fully mechanized top-coal caving face mining will cause dramatic changes in stope stress,large-scale destruction of coal body,severe migration of overburden rock,increase of goaf fracture space,and have a significant impact on gas release and migration.The analyzed gas migrates through the roof fracture space and accumulates in the goaf and upper corner,which has a serious impact on the mine production safety.Therefore,mastering the strata pressure behavior law and overlying rock fracture height development characteristics of high gas fully mechanized top-coal caving face can provide technical support for the reasonable layout of gas drilling in fully mechanized goaf.Taking 2303 working face of Zhujiao Coal Mine as the engineering background,on the basis of coal rock mechanics test and surrounding rock microstructure detection,the paper explores the roof stress distribution,plastic zone failure characteristics and "two zone" development height of the working face,compares the drainage effect of different goaf gas drainage pipe final hole height,and obtains a reasonable goaf gas drilling layout scheme.The main research results are as follows:(1)The strength of coal and rock in the roof and floor of 2303 working face is tested.The anti cohesion of coal is small and the stability is poor;The basic roof is hard rock.The microstructure of coal samples is observed.The coal samples have dense pores,few fissures,soft texture and strong gas storage capacity.(2)The roof mechanical model of fully mechanized top-coal caving face is established,and it is calculated that the roof will break in the middle of goaf first;The weighting step of roof is analyzed theoretically;The stress distribution,development characteristics of plastic zone,caving step and strength of 2303 working face are simulated by UDEC.The law of strata pressure and deformation characteristics of roadway are measured and analyzed.(3)The influence of mining thickness,proportion coefficient of hard rock,coal seam dip angle and mining depth on the height of "two zones" is explored;The height of "two zones" of 2303 working face is explored by UDEC.When the working face is advanced 130 m,the height of caving zone is about 21.7 m,and the height of fracture zone is about 45.0 m.The "two zones" height of 2303 working face is measured,and the height of caving zone is 18.8 m,and the height of fracture zone is 41.4 m.(4)The release of gas and the strata pressure on the working surface present a periodic response,and the release time is slightly lagging behind the time for strata pressure on the working surface.FLUENT is used to simulate the gas drainage effect of different drainage pipe end hole heights when the angle between the high-level drilling in the goaf and the coal seam is 30°.The results show that when the length of the drainage pipeline is 60 m and the vertical distance between the end of the borehole and the coal seam is 30 m,the gas drainage effect in the goaf is the best.There are 54 figures,14 tables and 99 references in this paper.