Study On Mechanism And Control Of Water Inrush From Damaged And Ruptured Floor Induced By Mining Disturbance And High Water Pressure In Deep Coal Mining

The deep coal mining in North China is increasingly threatened by the Ordovician limestone formation aquifer with high water pressure.The water inrush still occurs frequently from the coal seam floor after regional advanced treatment in deep mining above high confined water.The disturbance intensity of deep mining is enhanced,the risk of floor water inrush is increased,and the water inrush mechanism is more complex.Thus,this dissertation comprehensively adopts field investigation,theoretical analysis,laboratory test,physical simulation,numerical simulation and field test to study the key scientific problem that the formation mechanism of floor water inrush channel,taking the typical deep coal mining above aquifer as the engineering background,based on high-water pressure and mining disturbance effects.The floor water inrush characteristics and influencing factors in typical deep mining face are systematically studied,the rock failure characteristics and seepage characteristics under high water pressure and mining disturbance are analyzed,the mechanism of water inrush from damaged and ruptured floor induced by mining disturbance and high water pressure in deep coal mining are revealed,and the method of pressure relief control by roof hydraulic fracturing and multi parameter effect evaluation method are proposed and practiced in engineering.The main achievements are as follows:(1)By analyzing the typical cases of floor water inrush in deep mining,the characteristics and influencing factors of floor water inrush in typical deep high-water pressure and mining disturbed working face are obtained.The characteristics of floor water inrush are that under the combined action of high water pressure and strong mining disturbance,the floor fissures expand and penetrate or the structures are activated to develop into water inrush channels.Under the condition of thick water resisting strata or regional treatment,floor water inrush disasters still occur in some working faces.The influencing factors of floor water inrush are high in-situ stress,high confined water pressure,strong mining disturbance and fracture zone or fault.The floor water inrush mode in deep mining has the characteristics of deep occurrence environment,and the coupling effect between various factors is enhanced.(2)The uniaxial cyclic loading and unloading experiments of sandstone under mining disturbance stress path are carried out to analyze effect of different disturbance rates and disturbance amplitudes on rock strength and damage,and reveal the damage and failure law of rock in floor under mining disturbance.A triaxial unloading seepage experiment of fractured sandstone is designed to measure the permeability evolution of fractured sandstone under different confining pressure,different permeability pressure,confining pressure loading and unloading and step-by-step unloading confining pressure.The exponential relationship between permeability and effective unloading volume of confining pressure under different permeability pressure is determined.The quantitative relationship between fracture activity degree and unloading volume based on permeability evolution characteristics is established.The seepage evolution of floor fractured rock mass under high water pressure and mining disturbance is revealed.(3)Taking the mining conditions of Xingdong 2# coal seam in Hanxing mining area as the engineering background,this dissertation constructs a physical simulation model of the floor with concealed structure under mining disturbance and high water pressure.The evolution of fractures,displacement and acoustic emission of surrounding rock are analyzed.The evolution of fracture development,stress,displacement and infrared radiation near buried fault and the fractal characteristics of water-conducting fracture are obtained,the spatial and temporal evolution process of floor water inrush channel is reproduced,and the damage and rupture evolution of the floor under the joint action of deep high water pressure and strong mining disturbance and the law of water inrush caused by the activation of floor structure are revealed.(4)The stress field disturbance characteristics in mining floor were studied by using discrete element simulation software,the evolution of stress concentration zone and unloading arch of the floor under different weighting intervals are analyzed,and the evolution of the stress increment and deviator stress in different areas of the floor under different mining depths are studied.Based on the theory of elastic-plastic mechanics and rock mechanics,the calculation formula of floor failure depth under different disturbance intensity is derived,and the damage deepening law of the floor under deep mining disturbance is analyzed combined with numerical simulation.(5)Based on the fluid-solid coupling theory,the relationship between water pressure and mining disturbance is established.It is pointed out that the dynamic disturbance during roof periodic weighting leads to the excess pore water pressure in aquifer,which reduces the critical initial water pressure,enhances the hydraulic fracturing effect.The fracture at the top of the aquifer is hydraulically fractured and the rising height increases.Based on the fracture mechanics theory,a mechanical model of water bearing fracture extension under the combination of dynamic and static load is established,the formula of water pressure increment in fracture under dynamic load is derived,and the critical water pressure criterion of water bearing fracture extension by dynamic and static load disturbance considering water pressure increment is established.It shows that dynamic load disturbance increases the water pressure in fracture,decreases the critical water pressure of fracture extension,increases the range of fracture extension angle,and changes the most easily extended fracture dominant angle,and reduces the dynamic load increment required for crack extension.Based on the theory of unloading rock mass mechanics and fracture mechanics,the expansion and lifting mechanism of water bearing fracture in the floor under high water pressure and strong unloading is studied.It is found that the greater the seepage water pressure and unloading degree,the greater the unloading damage degree,the greater the unloading starting point stress,the greater the unloading damage degree of the fracture,and the larger the unloading amount of the maximum principal stress only needs the unloading amount of the minimum principal stress,and the unloading damage and failure of the water bearing fracture rock mass can occur.The critical safety factor of fracture propagation is established.It is found that reducing mining stress concentration,incoming dynamic load,mining unloading and increasing high confined water pressure will improve the safety factor.Finally,the mechanism of water inrush from the floor disturbed by mining above high confined water is revealed,and the corresponding water inrush prevention methods are put forward.(6)The mechanism of water inrush from damaged and ruptured floor induced by mining disturbance and high water pressure in deep coal mining is revealed to be that in the high stress environment,the strong mining disturbance such as mining unloading,stress concentration and incoming dynamic load leads to the drastic change of the stress field in the floor rock mass,resulting in the damage and failure of the floor rock and the activation of the structure,the increase of permeability and mining damage depth in the tectonic zone.Under the combined action of high water pressure and strong mining disturbance,the water pressure in the fracture increases,the hydraulic fracturing effect becomes higher,the water bearing fracture expands and penetrates to form a water diversion fracture network,and the high confined water conducts up.When the floor failure zone is connected with the hydraulic conductivity zone or the water conducting structure activation zone,the floor water inrush occurs.(7)The technology of floor water inrush prevention and control by roof hydraulic fracturing to mining pressure above confined aquifer is proposed,as well as the comprehensive evaluation method of floor pressure relief effect by multi-parameter monitoring such as mining stress,microseismic monitoring,borehole peep,water level monitoring and surrounding rock deformation,etc.The risk of floor water inrush is monitored in real time and the prevention and control effect is evaluated.In addition,the mechanical model under the combined action of mining stress and high water pressure is constructed.The failure mode of floor and the development depth of water conducting fracture before and after roof hydraulic fracturing are compared.The field monitoring results show that the prevention and control effect is proved to be effective.