Study On Deformation And Failure Depth Of Mining Floor In Extra-Thick Coal Seam Of Datong Mining Area

To explore the influence of mined thickness on the mining failure depth of complete floor,the geological and full-mechanized caving mining conditions of 8209 working face of extra-thick coal seam in Tongxin coal mine of Shanxi Province are taken as the background.The strain induction method was used to determine the depth of the floor failure zone in this working face is 20.9 m.The floor periodic weighting step distance of the working face is 15.0-20.0 m,while the roof periodic weighting step distance is 29.1-43.7 m,which indicates that the transmission of roof periodic weighting to the floor is greatly reduced by the buffer effect of extra-thick coal seam.Therefore,it was found that the extra-thick coal seam has a large buffer effect on the propagation of periodic weighting from roof to floor.On this basis,similar physical model test and numerical model of the working face were established.The macroscopic fracture and strain variation of similar material simulation,and the change in vertical stress and plastic zone of numerical simulation indicated that the coal seam floor failure depth of this working face is 22 m,which is consistent with the field measured results.The vertical stress propagation of numerical simulation also reflects the buffer effect of mining stress propagation in the floor of extra-thick coal seam.Based on the field measured data of floor,it is found that the single factor of mined thickness has little influence on the floor failure depth.Finally,based on the theory of mine pressure,the theoretical calculation improved the relevant formula,and a calculation formula of floor failure depth suitable for extra-thick coal seam was derived and proposed.To further explore the contribution of mined thickness to the floor,the author systematically collected and then analysed 61 sets of measurements from field data.Subsequently,we comprehensively analysed the influence of mined width,mined depth,coal seam dip angle and mined thickness on the failure depth in the complete floor of the mine by using the Deng's Grey Incidence Analysis model and numerical simulation.The results showed that the mined depth and mined width had the greatest impact on the failure depth,followed by dip angle of the coal seam,and mined thickness had the least impact,which is basically consistent with the research results of extra-thick coal seam in Datong mining area.In terms of the influence of the mined depth and mined width,it is found that when the mined depth is less than 500 m below the surface,the influence of the mined width is higher than the mined depth,but when the mined depth is more than 500 m below the surface,its influence is higher than the mined width.Therefore,we proposed that a mined depth of 500 m below the surface was the transition point into deep mining.At the same time,a multiple linear regression formula about the weight coefficient of floor hard rock is proposed,and based on the entropy method,a multiple nonlinear regression formula with only mined width and mined depth is proposed.The two regression formulas have strong accuracy.The research results have important practical reference value for the excavation support of extra-thick coal seam and the prevention and control of floor water disaster.There are 46 figures,19 tables and 119 references in this paper.