Coal Rock Migration Laws And Coal Caving Process Optimization Of Top Coal Longwall Caving In Wangjialing Coal Mine

In China's proven coal reserves,the thick coal seam accounted for more than 45%.It is of great significance to the efficient mining of thick coal seam.As the core technology of China's thick coal seam mining,how to improve the recovery rate of top coal is the key to the success of this technology.The degree of top coal crushing and whether it can be fully released after crushing have important effects on the recovery rate of top coal.Therefore,it is of great significance to reveal the failure mechanism,degree of fracture and law of top coal in fully mechanized caving mining under different technological parameters for realizing high yield and high efficiency of fully mechanized caving mining face.Taking the 12309 fully mechanized caving mining face of 2^#coal seam in wangjialing coal mine as the engineering background,the physical and mechanical parameters of surrounding rock and the distribution of in-situ stress are measured firstly.Then,based on the measured data,the influence of mining height on top coal failure and coal wall stability was simulated by FLAC^3Dnumerical simulation software.Because FLAC^3Dcould not simulate the caving characteristics of top coal,PFC^2Dnumerical simulation software was used to analyze the influence of machine mining height on the migration law and recovery rate of top coal;Secondly,by combining theoretical calculation with similar simulation experiment,the recovery rate of top coal under different coal discharge steps is analyzed.In addition,the caving regularity and top coal recovery of coal under different caving methods are studied on the basis of reasonable mining height and drawing interval.At last,the reasonable selection of mining equipment for 12309 fully mechanized caving face is analyzed based on reasonable caving process parameters.The main conclusions are as follows:(1)Based on the theory of fuzzy mathematics,the caving property of 2^#coal seam top coal under the influence of mining depth,coal seam strength,roof conditions and other natural factors is analyzed.It is considered that the caving property of the top coal of the 2^#coal seam belongs to class II,and the caving property is good.It is necessary to select reasonable caving process parameters to achieve high-yield and efficient mining of the working face.(2)The mechanical mining height has a significant influence on the destruction and release of top coal.By using FLAC^3Dnumerical simulation software,the influence of mining height on top coal failure characteristics and coal wall stability is analyzed.When the mining height is 3 m,the top coal in front of the coal wall and the top coal in the control area have the best failure effect.However,when the mining height is more than 3m,the horizontal displacement of coal wall increases abruptly and the stability of coal wall becomes worse.Through the PFC^2Dnumerical simulation software,the movement rule of top coal under different mining height is analyzed.It is concluded that the top coal recovery rate is the highest and the gangue content rate is the lowest when the mining height is 3m.Considering synthetically,it is considered that the safety of working face and the caving ability of top coal can be unified when the mining height of 3 m is adopted in 12309 working face.(3)Based on the ellipsoid theory,it is calculated that the best caving step is 0.83m under the geological conditions of 12309 working face.Because the shearer's section depth is 0.865m,the reasonable caving step is 0.865m,one mining and one caving.The theoretical calculation results are verified by the three-dimensional dispersion similar simulation experiment.It is concluded that when the caving step is one mining and one caving,the top coal recovery rate is the highest,and the circulating coal caving is relatively stable,so it is determined that the reasonable caving step distance of 12309 working face is0.865m.(4)Through PFC^2Dsimulation software,the top coal caving effect under different caving modes is studied.It was found that the top coal recovery rate and the gangue content of the double-wheel interval coal discharge were the highest and 91.1%and 6.7%respectively;the coal discharge effect of the single-wheel interval coal discharge method was not much different from it,and the top coal recovery rate and gangue content 90.6%and 7.2%respectively.Considering that the on-site double-wheel interval coal discharging process is complicated,difficult to control and has low production efficiency,it is considered that the single-wheel interval coal discharging method is more suitable for the 12309working face.(5)According to the actual conditions of the coal mine and the determined reasonable coal caving process parameters,the main mining equipment of 12309 working face is selected reasonably,and the process cooperation relationship of the production system is analyzed.It is considered that the selected equipment can meet the requirements of high yield and high efficiency of the fully mechanized coal caving working face.