Mechanism Of Water Inrush From Ordovician Limestone And Key Technology Of Prevention And Control In Deep Mining Seam Floor Of Hanxing Mining Area

With the increase of mining depth,the Ordovician limestone water pressure and the probability of water inrush increase.After water inrush,the cost of drainage increases with the increase of mining depth.Water inrush from floor not only threatens mine safety,but also greatly reduces mine economic benefits.The study of floor water inrush mechanism plays an important role in the prevention and treatment of water inrush.Based on the theoretical mechanics and numerical simulation,the different functions of floor rock in the occurrence of water inrush under the condition of deep mining are analyzed.It is found that the cracks in the strata with certain thickness under the mining failure zone of coal seam floor can be activated and lose the ability of water blocking when water inrush occurs.Taking a mine in Hanxing mining area as an example,this process is simulated by FLAC^3D,and the plastic fracture depth of floor rock and the minimum development depth of fracture activation zone are obtained.According to the different functions of coal seam floor strata in the formation process of water inrush channels,the floor strata under deep mining conditions can be divided into mining failure zone,fracture activation zone and potential lifting zone under the condition of deep mining.The fracture activation zone refers to the rock stratum in which the fracture can be activated and lose the water blocking ability under the influence of mining and high pressure water.The potential uplift zone is the minimum development range of the water inrush channel.Based on the study of distribution law of fracture development in coal measure strata in Hanxing coal mine area and the horizontal connectivity of horizontal fractures of thin limestone distributed in potential lifting zone on vertical fractures,it is found that the distribution of thin limestone in potential lifting zone leads to the increase of floor water inrush probability.The mechanism of Ordovician limestone water inrush in deep mining coal seam floor in Hanxing mining area can be generalized as follows:under the influence of mining,the failure zone and fracture activation zone of coal seam floor lose the ability to block high-pressure water;the thin limestone in the potential lifting zone connects the vertical water passage above and below,which increases the probability of water diversion channel connecting Ordovician limestone water and fracture activation zone,and forms water inrush.The deep Ordovician limestone is mainly composed of dissolution fissures,and the spatial form of connectivity is mainly"grid like".Based on the theoretical analysis of slurry migration in fractures,it is concluded that the main influencing factors of grouting are the type of injected medium and the viscosity of grout.Based on the analysis of the actual grouting pressure curve,it is concluded that the main types of grouting media are fracture type,cavity type and combination space type.By testing the time-varying process of viscosity of common specific gravity slurry,the time-varying characteristics of viscosity of different specific gravity slurry are obtained;the viscosity of cement slurry with specific gravity of 1.2 basically does not change with time,while the viscosity of cement slurry with specific gravity of 1.3 increases with time,but the increase range is small.The viscosity of cement slurry with specific gravity of 1.5 increases obviously with time.On the basis of the grouting treatment of uniform distribution horizontal boreholes,this paper puts forward the grouting control key in Ordovician limestone water rich aquifer:slurry control technology and process parameters of thick slurry low-pressure filling injection and thin slurry high-pressure supplement..