Characteristics and control technology of water inrush from deep coal seam floor above confined aquifer in Xingdong Coal Mine

To overcome the problem that the water inrush still occurs frequently from the coal seam floor after regional advanced treatment in deep mining above high confined water,the water inrush process and geological conditions of water inrush working faces in Xingdong Coal Mine of Hanxing mining area in recent years are analyzed by site investigation and theoretical analysis. The characteristics and influence factors of floor water inrush are investigated to determine the main controlling factors of floor water inrush. Based on elastic-plastic mechanics theory,the influence of different roof weighting steps on the floor failure depth and width is analyzed under the dynamic and static combined loading. Furthermore,the evolution law of floor mining stress field and floor plastic zone under different roof weighting steps are numerically simulated and analyzed. The results show that the violent site roof weighting result in water inrush is the key feature of floor water inrush,which is primarily induced by the stable roof in Xingdong Coal Mine. With the increase of roof weighting step,the stress concentration zone and the unloading stress arch gradually spread deeper to the floor rock mass,and the dynamic load occurs strongly when the roof collapses. The activation of concealed water conducting structures and the failure of deep rock masses is induced by the superimposition of static and dynamic loads. The floor failure zone connects easily with the water conducting channels such as the concealed structural zone. Therefore,the roof control technology using the hydraulic fracturing to prevent the floor water inrush as well as the multi parameter monitoring including microseismic monitoring,stress monitoring,surrounding rock deformation monitoring and the confined water level monitoring are proposed. The results on site monitoring show that the average periodic weighting step of the test face after the roof hydraulic fracturing is 9. 53 m,which is 61. 42% less than that of the adjacent working face without roof hydraulic fracturing. The dynamic load coefficient of periodic weighting,stress concentration coefficient and the deformation velocity of surrounding rock are smaller,and the Ordovician limestone water level remains stable,while the floor water inrush channels has not been formed. The floor water inrush is effectively controlled by the proposed control technology.