Study On Fracturing Mechanism Of Stope Roof During Combining Mining Of Closed Thin Coal Seam Group

Based on the Guandi Coal Mine of Shanxi coking coal Xishan Coal Electricity Group Company No.2 and No.3 coal seam as the engineering background,through theoretical calculation,numerical simulation and observation and other means to close thin coal seam combined mining roof breaking mechanism are analyzed deeply.The conclusions are as follows:1)According to Guandi mine No.2 and No.3 coal seam between the roof condition,close thin coal seam roof layer according to the lithology and joint fissures were divided into 3 types,namely: the unstable layer between roof structure and roof structure,moderately stable interlayer stability between layers of roof structure.According to the 3 layer of roof structure,the breaking form is divided into 3 kinds,namely the unstable layer of loose broken roof structure,moderately stable layer of roof structure for block breaking,stable layer of roof structure for slab breaking.2)Analysis of roof three kinds of roof structure layer in coal seam mining face in the process of breaking mechanism,pointed out that the unstable layer between the roof structure of loose broken,the structure strength is small,the layer will fall under the direct roof with coal mining and caving,and is the main way of slip dispersion between the blocks,the structure of the mine pressure appear very weak;the middle layer between the stability of roof structure for block broken,the broken way is to block the collapse and instability,the structure will have a certain pressure showing mine,but not severe;the stability of interlayer structure for the roof plate broken,because the structure of the interlayer roof is complete,so it is seen as a thin plate,and in the mining process in the layer of roof is O-X "broken forms,such as the roof structure layer direct roof rock Layer has a certain strength,will form a certain support structure,forming a cycle to pressure phenomenon,so its mine pressure is obvious.3)Based on the theory of sheet rock pressure,four different support models for plate structures in different mining processes are established,and their fracture laws are numerically solved.The first coal face direct roof first breaking is at the midpoint of the long side and a short side;the first coalface roof cycle breaking is the most in the center of long and short side of the solid solid edge distance goaf;continuous working face roof first breaking in long distance by solid edge empty area and short solid edge at the midpoint of the connection;face top cycle breaking in long distance goaf solid edge and short solid edge at.According to the engineering practice of the 3318 working face of Guandi Coal Seam,the data are brought into the formula calculation,and the initial pressure step distance of the 3318 working face is 21.4m,and the period to pressure step is 19.8m.4)Established on coal seam mining separate numerical simulation model of the roof caving and mining analysis of different pressure on coal seam distance,the roof fracture above the working face of direct roof rock on coal seam mining in the 25 m working face before,and periodic weighting distance is about 20 m.5)Three numerical simulation models of lower coal seam mining are set up under different roof structures.The subsidence of roof and the pressure of coal face in No.3 coal seam under different pushing distance are analyzed.For the unstable layer roof structure,due to the weak interlayer of direct roof shale and joint fissures,and the influence of mining on the coal seam,the direct roof is very loose structure broken,in the process of coal seam mining under the roof,the granular structure almost without any support effect of performance for the roof with the working face advancing continuously falling,this also explains the layer structure of mining roof strata pressure appears very weak.For the moderate stability between layers of roof structure,in the process of coal seam mining under the same roof,unstable layer structure is not the same,the roof structure with support ability,the immediate roof caving is not with adopt withemit,but relative to promote a 5~10m working face after lag distance.This is explained,between this kind of roof structure all the blocks in the mining process in the formation of mutual support,but because of its block size limit,and not long distance support,so will the 5~10m lag distance.The stable layer of roof structure,in the process of mining coal seam,the direct roof is hard rock formation structure similar to that of thin plate,so in the mining process,can appear the first caving,the phenomenon of periodic caving.In the layer distance,the immediate roof is thick hard rock conditions,through the above analysis can be obtained under the first coal seam working face No.3 direct top caving step in coal seam No.3 coal face top boom caving step around.6)Based on the data of 3318 working face provided by Guandi Coal Mine,the law of rock pressure data at 3318 working face is analyzed.It is concluded that the first step pressure distance of 3318 working face is 23.8m,and that of 3318 working face is 21.3m.This is consistent with the previous theoretical calculations and numerical simulations.