A Study Of Evolution Characteristics On Overburden & Two Belts During The Mining Of Thick Seam In Zhangshigou Coal Mine

Safe and water-retaining mining is an important part of green mining technology.It is of great significance for mine water control and water resource protection to study the overburden fracture mechanism of goaf and the development height of waterconducting zone when mining under water body.The average thickness of 15#coal seam in Zhangshigou Coal Mine,Gaoping City,Shanxi Province is 4.1m.In order to study the development law of overburden "two zones" in thick seam mining of this coal mine and ensure safe recovery of 15#coal seam in Zhangshigou Coal Mine,taking 15102 working face as engineering background,the characteristics of overburden breakage and the height evolution mechanism of "two zones" in thick seam mining are studied by numerical simulation,theoretical analysis and field observation.The research results can provide reference for the follow-up mining work of the mine.The main results are as follows:(1)According to production geology and hydrogeological conditions of Zhangshigou Coal Mine,the distribution of strata and water-bearing and waterinsulating layers of 15102 working face is obtained: aquifers above 15# coal seam are weak water-rich aquifers,and water-insulating capacity of interlayer mudstone waterinsulating layer is general;By calculating the lithological evaluation coefficient of overburden,it is determined that the overburden lithology of 15# coal seam in 15102 working face is weak,slightly medium and hard.(2)The numerical simulation analysis of overburden fracture process caused by coal seam goaf shows that the height of overburden collapse zone is 18.2m,the ratio of collapse zone to mining thickness is 4.44,the height of water conduction-zone is 53.8m,the ratio of water conduction-zone to mining thickness is 13.12 and the first collapse step of overburden rock is 50 m in 15102 working face 15#coal seam.Separation development within the water conduction-zone generally goes through three stages:rapid development,slow closure and stable maintenance.The water conduction fissures often occur after the separation develops to a certain extent.The height evolution of the water conduction fissure zone can be divided into four stages: rapid development,temporary stability,re-development and stable maintenance.(3)The two methods of double-end plugging leakage measurement and borehole television image are used to detect the "two zones" height of overburden rock in 15#coal seam of 15102 working face.The measured height of water conduction-zone is48.34 m and the ratio of water conduction-zone to mining thickness is 11.79.The measured results basically coincide with the developed height of the water conduction-zone by numerical simulation.(4)Comparing and analyzing the empirical formulas of the height of the two zones,the result shows that the empirical formulas given in the “Detailed Rules for Coal Mine Prevention and Control of Water(Interpretation)” are most suitable for coal mines with similar mining geological conditions,and the height of the collapse zone is 22.07 m,the ratio of collapse zone to mining thickness is 5.38,the height of the water-conducting fissure zone is 50.34 m and the height of water conduction-zone is 12.28;Based on the theory of "key strata" and "masonry beam",a calculation method is put forward to get the development height of water-conducting fissure zone by judging the fracture state of soft and hard rock strata respectively.The development height of water-conducting fissure zone is 48.99 m and the fracture-recovery ratio is 11.95.The height comparison of water conduction fractured zone obtained by different methods shows that the error between the height of water conduction fractured zone obtained by judging the fractured state of rock layer and the measured result is the smallest(2.1%).