Analysis Of Roof Stability Of No.8 Coal Seam In Sitai Mine,Datong Coalfield

Sitai Coal Mine in Datong coalfield is located in the west of Datong City.It mainly mines No.8 coal seam in the lower part of Taiyuan Formation of Upper Carboniferous.Multiple small folds,4 faults with a drop greater than 10m and 3 collapse columns are developed in the mine field;A diabase dyke with a length of about 3800 meters and a width of about 10 meters extending in the northeast direction is exposed in the southeast.The underground discovery shows that the rock of the coal seam is broken and the thickness of the coal seam varies greatly over a short distance,with searious fluctuation.Based on this,the geological characteristics of the coal seam roof in Sitai mine are analyzed in detail,and then the stability of the coal seam roof is comprehensively evaluated.Based on the comprehensive collection of relevant geological,drilling and underground production data of Sitai Mine in Datong coalfield,all data are summarized and sorted,and the characteristics of coal seam roof are analyzed.The failure depth of coal seam roof is numerically simulated by FLAC^3Dsoftware,and the simulation results are compared with the theoretical calculation values;Various factors affecting roof stability of coal seam are comprehensively analyzed and the evaluation indexes are determined.Analytic hierarchy process,entropy weight method and coefficient of variation method were used to calculate the weight value of each evaluation index;The weight obtained by analytic hierarchy process is coupled with the weight of entropy weight method and coefficient of variation method to obtain the comprehensive weight;The vulnerability index method is used to build the model for two comprehensive weights,and Arc GIS software is used for superposition analysis to draw the zoning map of coal seam roof stability.The results show that the simulated failure depth of coal seam roof is 54m,and the failure depth calculated by empirical formula is 54.7m,which proves that the simulation is reasonable and effective;The factors affecting the stability of coal seam roof are divided into two categories:lithologic characteristics and other characteristics,including six aspects:pseudo roof thickness,direct roof thickness,average layered thickness of direct roof,main roof thickness,roof rock combination effect and fault fractal dimension;The comprehensive weights of analytic hierarchy process and entropy weight method are 0.0726,0.1800,0.0811,0.4642,0.1666 and 0.0355 respectively;The comprehensive weights of analytic hierarchy process and coefficient of variation method are 0.1603,0.1920,0.0927,0.4025,0.1113 and 0.0412 respectively;Based on the two comprehensive weights,Arc GIS is used to draw the partition map of coal seam roof stability in Sitai mine.The research is divided into five types:roof stability area,roof relatively stable area,roof stable transition area,roof unstable area and roof extremely unstable area.Through comparative analysis,the roof transition zone and roof instability zone account for the largest proportion in the study area,and the classification areas are roughly the same.Only the roof transition zone and instability zone are slightly different in the middle of the study area.Therefore,the two combined methods can be used to evaluate the stability of coal seam roof and guide mine safety production.There are 33 figures,25 tables and 88 references.