Study On Experimental Simulation Method For Water-proof Stability Of Mining Overlying Rocks

Coal mining in China is gradually moving towards the northwest.However,most of the northwest coalfields are located in arid and semi-arid climatic areas,where water resources are scarce.When large-scale mechanized mining is carried out by traditional methods,water resources are often lost and ecological deterioration is caused.Therefore,it has especially important meaning to study the ways of water resources protection and exploitation.Based on the geological background of Yili No.4 Mine,Xinjiang,this paper studies the stability of water-proof ability of mining overburden.Based on the elastic foundation beam theory,the foundation beam model of long-wall mining and the foundation beam model of strip mining are established to explore the stability of overburden by mining.Similar material of aquifer is developed by using fluid-solid coupling similarity simulation theory.Through water-rock similarity simulation test,the development law of water-conducting fracture zone in long-wall mining and strip mining is analyzed,and the results are compared by using numerical simulation software to get a reasonable way of water resources protection and exploitation.The major research contents and conclusion are as follows:(1)The hydrogeological conditions of Yili No.4 Mine in Xinjiang are analyzed.The mechanical and hydraulic properties of mudstone with water-proof significance are tested and analyzed through laboratory experiments.The basic data of uniaxial compressive strength,tensile strength,water absorption,swelling rate and permeability of mudstone are obtained.(2)Based on the theory of elastic foundation beam,the foundation beam model of long-wall mining and strip mining are established,and the deflection equation of water-proof layer in two kinds of mechanical models is deduced.Through the analysis of examples,the maximum deflection value of key rock beam is 0.2248 m in strip mining mode,and 4.7191 m in long wall mining mode.Therefore,strip mining can effectively control the deformation and destruction of rock strata,thus ensuring the water-proof ability of water-proof layer and realizing the protection and exploitation of water resources.(3)Based on the fluid-structure coupling similarity theory,the water-proof layer analogue material is developed with five kinds of materials easily available in life.Through orthogonal test method,25 groups of test schemes with 4 factors and 5 levels are designed.The mechanical and hydraulic characteristics are tested and analyzed.Finally,the similar proportion of water-proof layer material is developed,and the water-proof performance of the material is verified by similar simulation test.Similar materials prepared have large mechanical properties and hydraulic spans,so they can meet the similar proportioning requirements of different kinds of materials.(4)Through the water-rock two-phase similarity simulation test,the law of overburden failure and seepage in the working face of No.4 Coal Mine in Yili,Xinjiang is studied.The law of overburden stress change,strata displacement change and water level change in the mining process are analyzed.The results are compared with those of physical similarity simulation test by using 3D EC discrete element numerical simulation software.The results show that when the long-wall mining method is used to excavate to 140 m,the height of the water-conducting fracture zone develops to the phreatic aquifer,and the tension fracture is formed at the top of the model.The water in the phreatic layer loses rapidly,and the displacement of overlying strata changes in a "U" type.Using strip mining method,one overlying strata water-conducting fracture zone develops to 33.6 m away from coal seam,and two overlying strata water-conducting fracture zone develops to 58.8 m away from coal seam.Water-conducting fracture never penetrates into diving aquifer,and the displacement change of overlying strata presents "W" type.