Study On Mechanism Of Flood Inrush From Floor Of Structure With Concealed Subsidence Column In Confined Water

With the shallow coal seam resources being gradually exhausted and the coal mine production gradually turning to the deep,the danger of mine water hazard to the safety of coal mine production is increasing.Among many water inrush accidents,coal-bearing subsidence pillar is one of the most important factors causing mine water disaster.In addition,most of the subsidence pillars of coal measures exist in concealed form and are widely distributed in the coal-bearing rock series of the Late Paleozoic(Liaoning-Hebei-Shanxi-Shanxi-Shanxi-Henan-Anhui-Su Coalfield)and Mesozoic(Datong Coalfield)in North China and the Late Triassic Xuhe Formation in South China.In-depth study of water inrush mechanism of hidden collapse column under mining disturbance is of great significance to the prevention and control of water inrush from hidden collapse column,and can also improve the safety of coal mine production.(1)Through collecting,collating and summarizing the research results of water inrush from coal floor and subsidence column,the distribution characteristics of subsidence column and the current research status of water inrush from floor,subsidence column and similar material simulation test are understood.(2)The formation mechanism of collapse column is discussed by analyzing the chemical composition of rock and the erosion of flowing water on rock.Then the influence of the size of collapse column,confined water pressure and micro-fissures on the water diversion of collapse column is obtained by using Griffith strength theory and fracture mechanics theory.(3)Through the combination of similar material simulation test and self-designed real-time monitoring system of confined water level,this paper mainly studies the influence of circular platform-type subsidence column without associated faults on floor stress distribution,floor crack development characteristics and confined water conduction law.The results show that due to the existence of collapse column,the stress concentration occurs in front of the collapse column,and the peak stress distribution is about 30m away from the collapse column,and the communication between the floor cracks and the collapse column also occurs near this location.In general,the velocity of confined water conduction increases first,then decreases and finally stabilizes,which is basically consistent with the law of floor stress change,and the water inrush from collapse column is sudden.(4)The FLAC3D numerical simulation software is used to simulate the water inrush mechanism of collapse columns with different shapes and with or without associated faults in six models.The water inrush mechanism of collapse columns with different shapes and with or without associated faults is studied from three aspects:floor stress,plastic zone and pore water pressure.From the characteristics of stress distribution,it can be seen that there are differences in stress concentration,stress peak position and stress peak value of collapsed columns with different shapes.The existence of associated faults makes the stress concentration greater and the peak stress occurs earlier.From the distribution characteristics of the floor plastic zone,it can be seen that the mining effect begins to affect the collapse column about 50 meters before the collapse column,and advances to the communication between the floor plastic zone and the collapse column plastic zone about 30 meters away from the collapse column.The plastic zone of the collapse column mainly concentrates on the boundary of the collapse column near the working face once,and the collapse column is relatively stable.Comparing the cases with associated faults and without associated faults,it is found that the plastic zone of floor communicates with the plastic zone of collapse column earlier.From the distribution characteristics of pore water pressure,it can be seen that the existence of subsidence column makes the pore water pressure concentrated area deflect to the direction of subsidence column.Associated faults aggravate the concentration of water pressure,expand the influence scope of collapse column,and increase the risk of collapse column.(5)By means of floor strain gauge,the paper also monitors the floor damage of hidden subsidence column under 9102 working face after grouting modification.The measuring points are arranged in the position where the water inrush is most likely to occur,and the deformation and failure law and the maximum damage depth of the floor after grouting are obtained.The results are compared with the failure depth of the whole floor and the floor before grouting to verify the validity of the grouting results.