Study On Characteristics And Control Of Rock Pressure Of Hard Roof In Fully Mechanized Top Coal Caving Mining With Large Mining Height In Tashan Mine

In the Datong mining area,the reserves of the Carboniferous Permian coal seam is as high as 385 billion tons.Most of the occurrence conditions belong to the extra thick coal seam.Taking the Tashan mine as an example,the average mining thickness of the coal seam 3-5~#coal seam in the main coal seam is about16m,the mining geological conditions are complex,and the coal seam in Datong mining area has"two hard"characteristics.Therefore,on the basis of integrating the related data of the one and two plate area of the Tashan mine,the theoretical analysis,numerical simulation and field measurement are used to synthetically study the regularity of the ore pressure and the effect of the hydraulic fracturing control of the hard roof.(1)Based on the geological data of the two plate area of the Tashan mine,the key strata of the"masonry beam"and the"key block"theory are determined to be No.4 medium grain sandstone and No.8 fine sandstone.The initial pressure step distance of No.4 medium grain sandstone is 51.43 to 62.99m,and the periodic pressure step distance is 26m,and the initial pressure step distance of No.8 fine sandstone is 115.11 to 140..99m,the periodic pressure step is57.5m.(2)It is concluded that the central structure of the fully mechanized caving face of the Tashan mining high mining face is a"cantilever beam masonry beam"composite structure,and the scope and pressure conditions of the lower direct top are No.1~3,the upper direct top is 4~7,the lower basic top is No.8~11,the upper top is the 12 layer and above(see table 2-2).(3)The mechanical model of"masonry beam cantilever beam"was constructed and perfected,and the mechanical model of the initial pressure and periodic pressure of the lower basic top was constructed,and the calculation formula for the working resistance of the stents needed for the initial pressure and periodic pressure was deduced.(4)Through the analysis of the ore pressure law of the two typical working faces of the Tashan mine and 8108(under the goaf),the correctness of the mechanical calculation is verified.At the same time,it is concluded that the effective means of reducing the ore pressure in the Tashan mine is to exploit the upper 4 coal seam in the place where the mining conditions are available.(5)Through the simulation of UDEC numerical simulation software,it is found that if the hydraulic fracturing is sufficient and the hydraulic fracturing measures are taken,the theory and the measured initial pressure step distance from 55 to 60m can be shortened by about half the distance,the roof subsidence is in the range of 12 to 22cm,and the working face is pressed and repeated in a large and small period,small Periodic pressure distance is 18~27m,and the large cycle pressure distance is 42~51m,which is basically consistent with the theoretical derivation and measurement.