| This paper takes the Yushen mining area,which is located in arid and semi-arid areas and has fragile ecological environment,as the research background,the mine water inrush and sand burst accidents and surface ecological environment problems caused by highintensity mining technology;The main research object is that the second water barrier is induced to break and become unstable under the comprehensive influence of the strong hydrodynamic pressure above it and the strong ground pressure caused by the instability and breaking of the first bedrock water barrier below,resulting in water inrush and sand burst accidents in the mine.By means of triaxial mechanical test,theoretical analysis,physical simulation test of similar materials,fluid solid coupling numerical simulation test and field test,this paper studies the relevant contents of water and sand inrush mechanism and water control mining mode of overburden rock under strong mining conditions in Yushen mining area.Based on the analysis of the natural geographical and geological conditions of caojiatan mine in Yushen mining area,the mine water filling conditions,the types of overlying rock mass and physical and mechanical properties of the coal seam are systematically summarized.Based on the analysis of the natural geographical and geological conditions of caojiatan mine in Yushen mining area,the mine water filling conditions and the types and physical and mechanical properties of the overlying rock mass of the coal seam are systematically summarized;The damage and seepage evolution law of overburden rock mass under the influence of different mining stress are studied through indoor triaxial permeability test;Combined with the field measurement results,the calculation formula of the development height of water diversion fracture zone in high-strength mining in Yushen mining area is fitted and revised.Based on the relationship between the sedimentary thickness of bedrock and the fracture development height after mining,the thickness standards of thick bedrock,medium thick bedrock,thin bedrock and ultra-thin foundation rock are divided and defined;At the same time,the law of ecological damage of overburden and surface under different mining intensity is obtained by using indoor physical simulation test and fluid solid coupling numerical simulation test;By analyzing the main influencing factors of water inrush and sand break accidents,and combined with the catastrophe critical criterion of water resisting soil layer deduced based on the key layer theory and material mechanics theory,the geological conceptual model of water inrush and sand break under the condition of strong mining is established;Based on the evaluation index system of water inrush and sand burst of AHP,the quantitative evaluation model of water inrush and sand burst risk of strong mining overburden is constructed,and the risk zoning of water inrush and sand burst is carried out,and then the evaluation method of mine water inrush and sand burst under the condition of strong mining in ecologically fragile mining areas is formed;Finally,based on the mining contradiction characteristics between coal resources and stratum ecological environment in the west,combined with the "coal water" dual resource coordinated mining theory,the "coal water" dual resource coordinated mining model in ecologically fragile mining areas is proposed,and its accuracy is verified by practical engineering application.The relevant research content of this paper is of great significance to enrich the risk assessment and prevention of roof water disaster.At the same time,it can provide theoretical guidance for green,safe and efficient mining in ecologically fragile mining areas.The main research results are as follows:(1)The permeability test results of overlying rocks in coal seam show that the permeability of sandstone is mainly affected by internal and external factors,the internal factors are directly affected by the closure of primary fractures and the expansion of shear fractures,and the external factors are affected by the change of confining pressure and osmotic pressure difference.Under the same confining pressure,under the action of seepage water pressure,the sandstone itself will change from brittleness to ductility,which will affect the strength and permeability of sandstone itself.(2)An orthogonal test scheme with different proportions of river sand,bentonite,clay,calcium carbonate,gypsum and paraffin as similar material components was constructed.A total of 25 groups of mechanical and hydraulic properties of similar materials of N2 impermeable soil layer under different proportions were tested by triaxial seepage meter,Through the analysis of range and variance,it is concluded that the factors affecting the uniaxial strength of similar materials from strong to weak are a(river sand:clay)> C(calcium carbonate: Gypsum)> d(river sand: Paraffin)> b(river sand:bentonite);The factors affecting the hydraulic properties of similar materials from strong to weak are d(river sand: Paraffin)> b(river sand: bentonite)> C(calcium carbonate:Gypsum)> A(river sand: clay),and the optimal ratio of similar materials in N2 impermeable soil layer is determined.(3)Through the physical simulation test of similar materials and FLAC3 D fluid solid coupling numerical simulation,the fracture evolution law and rock settlement deformation law characteristics of the first rock layer water barrier and the second soil layer water barrier in the mining process are analyzed.It is concluded that N2 laterite layer with a certain thickness can be used as the key layer and can block the hydraulic connection between Quaternary Salawusu formation aquifer and bedrock water.At the same time,the influence characteristics of overburden(soil layer)fracture evolution and dynamic evolution of aquifer pore water pressure are positively correlated with the length of working face and the thickness of mining coal seam.(4)According to the analysis of the detection results of the "two zones" observation holes constructed in the study area,the range of fracture mining ratio after mining is 19.07～ 20.38,and the range of collapse mining ratio is 4.79 ～ 4.96.Based on the statistical analysis of the existing development height of "two zones" in Yushen mining area,a height prediction model of water diversion fracture zone suitable for the western mining area of Yushen mining area is put forward.At the same time,based on the relationship between the sedimentary thickness of bedrock and the height of fracture development after mining,the thickness standards of thick bedrock,medium thick bedrock,thin bedrock and ultra-thin bedrock are determined and defined.Based on the measured results and degree analysis of surface ecological damage under high-intensity mining,it is concluded that the maximum surface subsidence after mining is 5.52 M and the subsidence rate is q = 0.502.(5)The water bearing sand layer,the water yield and Recharge Characteristics of the aquifer,the thickness of the effective clay layer,the thickness ratio of bedrock to loose layer and mining fissures are systematically summarized and selected as the key influencing factors of water inrush and sand break.Combined with the theory of material mechanics,the catastrophe criterion of the key water resisting layer of water inrush and sand break is deduced and calculated;At the same time,the evaluation indexes are classified and normalized.On this basis,the weight of each evaluation criterion and evaluation factor is determined by using the analytic hierarchy process(AHP)theory.By calculating the water inrush and sand burst risk index RI of each index factor,the thematic map of water inrush and sand burst risk of each evaluation criterion of mining overburden fractures is established,the quantitative evaluation model of water inrush and sand burst risk of mining overburden fractures is constructed,and the zoning evaluation of water inrush and sand burst risk is carried out.(6)On the basis of systematically summarizing the contradiction between coal mining and stratum ecological environment in xianyushen mining area,and based on the connotation of "coal water" dual resource mine construction,this paper puts forward the water control mining mode in ecologically fragile areas,that is,the cross policy of "three inspections,certain,two verification and two tracking".The four parts of the collaborative mining model complement each other and restrict each other.It abandons the inappropriate practice of studying "mine geology,mining methods and ecological environment" separately.Using this model can not only maximize the utilization of coal resources in the mining area,but also achieve the goal of green and safe mining.(7)Based on the research,the disaster mechanism and water control mining mode of overburden breaking and instability,water and sand burst in Yushen mining area are obtained.Combined with the geological and hydrogeological situation of caojiatan122107 working face,a method to determine the mining parameters of the working face in blocks on the premise of the comprehensive bearing capacity of the stratum and surface of the working face is put forward.The process flow can be divided into four areas,namely: height limited mining area,mining only and non caving area,dynamic height limited area and all mining areas.Through the idea of gradually increasing mining height in this block,the coordinated development of the damage degree of mining overburden formation and the bearing capacity of formation fragile area can be realized,and the accuracy of this method is verified by the dynamic change of water inflow in the process of mining... |
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