Failure Characteristics And Water-inrush Mechanism Of An Inclined Coal Seam Floor

At present, water-inrush from coal seam floor is a problem that serious threatens to the safety production in coal mine. Water-inrush is a phenomenon that when mining is carried out above a confined aquifer, the combined action of mining pressure and hydraulic pressure may induce the deformation failure of coal seam floor and large confined water inrush into mining space. For a long time, many scholars have made a large number research on the deformation failure, water-inrush mechanism and water-inrush prediction of the nearly horizontal and gently inclined coal seam floor, and have achieved the comparatively abundant research achievements which perform an important directive function to the safety mining above a confined aquifer. However, the theoretical research on the deformation failure, water-inrush mechanism and water-inrush prediction of an inclined coal seam floor is not adequate, and must be investigated further. So in the present paper, from the perspective of the combined action of mining pressure and hydraulic pressure, we used theoretical analysis, numerical calculation combined with the field monitoring to systematic research on the deformation failure, water-inrush mechanism and water-inrush prediction of an inclined coal seam floor, and obtained some innovative achievements as follows:(1) According to the overburden load distribution characteristics of an inclined coal seam, we established a mechanical analysis model of coal seam floor failure characteristic along the tilted direction of coal seam, using the theory of elasticity combined with Mohr-Coulomb yield criterion, and we deduced the stress expressions at any point of floor strata along the tilted direction of coal seam and the calculation formula of floor failure depth.(2) On the basis of the occurrence features of an inclined coal seam, using the software FLAC3D, we established a three-dimensional numerical calculation model of an inclined coal seam workface with longwall mining, simulated and analyzed the distribution law of stress, failure depth and failure form of floor strata along the tilted direction of coal seam at different mining depth, different workface width and different coal seam pitch.(3) Based on the load distribution characteristics of an inclined coal seam floor above a confined aquifer, we established a mechanical analysis model of water-resisting key strata of an inclined coal seam floor with the load of linear increased hydraulic pressure, using the theory of elasticity combined with Mohr-Coulomb yield criterion, and calculated the ultimate hydraulic pressure that the water-resisting key strata of inclined coal seam floor can bear, and deduced the mechanical criterion expressions of water-inrush from an inclined coal seam floor, which can provide a theoretical basis to predict the water-inrush from an inclined coal seam floor in the field.(4) From the view of the fluid-solid coupling, using the software FLAC3D, we established a three-dimensional fluid-solid coupling numerical calculation model of an inclined coal seam floor above a confined aquifer, simulated and analyzed the deformation failure, intrusion of confined water and the location prone to water-inrush of an inclined coal seam floor under the combined action of mining pressure and hydraulic pressure, which can provide a theoretical basis to determine areas in an inclined coal seam floor prone to water-inrush in the field.(5) We used a high-precision micro-seismic monitoring technique to continuous and dynamic monitor the 1066 workface floor strata of an inclined coal seam above a confined aquifer at Taoyuan Coal Mine, and determined the areas prone to water-inrush. Combined the water-inrush prediction result obtained by the water-inrush criterion of an inclined coal seam floor, through grouting consolidation the dangerous areas prone to water-inrush, we have achieved safe and highly efficient mining of the 1066 inclined coal seam above the confined aquifer at the Taoyuan coal mine successfully.The research achievements above can provide an important directive function to the inclined coal seam safety mining above a confined aquifer.