Failure Characteristics And Mitigation Technology Of Unconsolidated Aquifer Induced By Under High-intensity Mining

As coal resources in the mid-east region of China are gradually exhausted,the strategic focus of coal mining has been moved to the west area.The northwest region is rich in coal resources and the geological condition of coal seams is simple.With the continuous improvement of mining technology and equipment level,Internet + and intelligence,it is expected to be very suitable for high-intensity mining technology in this region.In the moment,the high-intensity mining technology of thick coal seams has been an important developing direction.However,northwest China is just an arid and semi-arid region.Under the effect of the unique climatic environment conditions,high-intensity mining results in a series of serious environmental problems,such as groundwater resource loss,surface destruction,grassland desertification and so on,especially the mining influence on unconsolidated aquifer in Quaternary.Therefore,it is of great theoretical and practical significance for the fragile ecological environment in western China to study the failure characteristics and prevention and control techniques of high-intensity mining on loose aquifer.In this paper,with the theoretical analysis,similarity simulation,numerical simulation and field monitoring used,the failure characteristics and prevention and control techniques of high-intensity mining on loose aquifer are studied.The main research results are as follows:(1)The definition of high-intensity mining and its present situation in thick coal seam is studied.Based on the collected data of high-intensity mining area in northwest China,characteristics of high intensity mining technology are put forward,and their reasonability is also verified by the method of analytic hierarchy process.The index system of high-intensity mining is also constructed.It is pointed out that the negative externality of high-intensity mining is the same as the influence of mining on the failure of the technical characteristics of high-intensity mining,which is characterized with group-occurring,sudden-occurring,chain-occurring and so on.(2)The importance of protecting the unconsolidated aquifer is analyzed by evaluating the quality of mine water.The failure characteristics and fracture propagation rules of overburden rock under high-intensity mining were studied with the help of similar simulation test.And it is pointed out that the main reason threatening the safety and stability of the unconsolidated aquifer is the penetrating fracture formed by the connection between upward and downward fractures.The failure characteristics of the unconsolidated aquifer under high-intensity mining conditions were detected and verified by transient electromagnetic method in the adjacent well field.(3)The rules of seepage fracture propagation in overburden rock with or without water pressure and their influence on the unconsolidated aquifer were contrasted by numerical simulation.The influence of downward fracture on the unconsolidated aquifer is studied by soli test.The principle of load transfer in unconsolidated aquifer is stated.And it is thought that the reason of the support crushing accident,which threatens safe mining of the working face by inrushing water in working face is caused by composite fracture of overburden rock,which is influenced by the unconsolidated aquifer.(4)From the macroscopic perspective,the failure mechanism of consolidated aquifer under high-intensity mining is revealed based on the theory of elastic plates,clamped beam and compactness.The newly generated penetrating fracture is the macroscopic reason of the failure of consolidated aquifer.The connection between the original fracture and newly generated fracture caused by the increasement of the porosity among the soil particles is the mesoscopic reason of the failure of the consolidated aquifer.(5)According to the prevention and control thought of unconsolidated aquifer failure,the green coordinated mining technology of strip mining roadway backfilling method,which is combined strip mining with filling mining technology,was proposed and designed.On the basis of this technology,considering the late transformation and upgrading of the mine,the development and utilization of underground cavity and the reduction of shallow-buried coal resources,the in-situ protection technology of unconsolidated aquifer is put forward.The technical system of prevention and control of unconsolidated aquifer is constructed,which provides technical support for the win-win situation of unconsolidated aquifer stability and working face mining safety.