Study On Deformation And Failure Regular Of Weak Cemented Overburden In Tashidian No.2 Coal Mine

Tashidian Mining Area is located in Tashidian Town,Korla City,Bazhou Prefecture,Xinjiang Province,which is an important coal energy base in Bazhou.Through the analysis of the strata data in the mining area and the relevant experimental data of the early exploration,it is concluded that the rock strata structure in the mining area is dominated by mudstone cementation with low overall strength.The uniaxial compressive strength of most of the rock strata is less than 30 MPa,which has the characteristics of loose structure and easy weathering.Therefore,it can be determined that the overburden of the mining area is weakly cemented rock.The research object of this paper is the W8203 fully-mechanized mining face of Tashidian No.2 Coal Mine.The research method combining the simulation test of similar material physical model,numerical simulation test and theoretical analysis is adopted to study the deformation and failure law of weakly cemented overbearing rock and the evolution law of water-conducting crack in the process of coal seam mining.Then,the prediction method of the development height of the water-conducting fissure zone in the roof is deduced.The main conclusions are as follows:(1)comprehensive W8203 similar material model test results of fully mechanized working face,PFC2 D numerical simulation analysis of the test results and the stability of the key stratum structure as a result,the thickness of 96.85 m can be drawn from gravel strata as the main key stratum,the main key stratum is not completely broken and no transfixion crack,hinged structure of rock mass after sinking to form stable,It provides a good support for the overlying strata.The caving zone,fracture zone and slow subsidence zone of the overlying strata on the W8203 fully mechanized mining face are all developed.(2)The development height of water-conducting fissure in the roof of coal seam does not simply increase linearly with the advancing distance of working face,but has a certain stagnation and mutation.The development height of the water-conducting fracture zone is controlled by the key strata.When the key strata or sub-key strata do not break,the water-conducting fracture will stagnate and develop upward.When the critical or sub-critical strata are broken,the water-conducting fissure will mutate upward,but there will be a certain "climbing" stage in the process of mutation development.According to the results of the similar material physical model test,the development height of the water-conducting fracture zone is 246.38 m,which is basically consistent with the experimental results of PFC2 D numerical simulation.(3)The height of water-conducting fracture zone calculated according to the empirical formula is smaller than the actual value,which is not suitable for fully mechanized mining of medium thick coal seam at one time.The residual dilatancy coefficient of weakly consolidated overburden is small,and the value of residual dilatancy coefficient of the prediction method based on the position of key layers is too large,which leads to the small prediction value of the height of water-conducting fracture zone in the roof of weakly consolidated overburden.In this paper,by organically combining the prediction method based on the position of key strata,the breaking and swelling characteristics of weakly cemented overburden,the empirical formula of large mining height and the judgment of the structural stability of the main key strata,a new method based on the position of key strata to predict the development height of waterconducting fracture zone in the roof of deep coal seam with large mining height and weakly cemented overburden is developed.