Analyzing Stability Synthetically And Researching Treatment Methods On The Complicated Multi-layer Mine-out Areas

With the rapid development of China's national economy, the demand for natural resources is growing, especially mineral resources. Although the great economic benefits are obtained in the course of mineral exploitation, a vatiety of geologic disasters are caused because of the complicated multi-layer mined-out areas formed by unscientific mining or civil predatory mining. It is caught high regard from the government and enterprises. Therefore, researching the stability and treatment methods of the complicated multi-layer mined-out areas are urgent affairs.Based on a large number of data about actual survey exploration and test, the synthetic judgment model of the two-stage fuzzy of the stability of mined-out area is made by using multi-stage fuzzy synthetic judgment theory and analyzing its failure modes and influencing factors synthetically. The model includes 3 hierarchies,4 factors and 16 genes. And all mined-out areas in Gaofeng NO.105 mine body can be divided into stable mined-out area I, local instable mined-out area II and instable mined-out areaâ…¢. Different and reasonable treatment methods should be adaptd to different mined-out areas on the basis of their actual stability.By using finite element software-FLAC3D, Numerical simulation is made to the three-dimensional model of the complicated multi-layer mined-out areas in Gaofeng NO.105 mine body from the view of rock mechanics. Through choosing the mined-out areas those have less than 30m thickness or big span of roof to be subject investigated, the thesis does not only research their stress distributing and plastic zone which are about the aspect of plasticity strength destroy, but also displacement monitoring of roof midpoint which is about deformation controlling. In addition, the stability of all 21 mined-out areas are classified. The classification result shows that there is little difference with stability classification of NO.13 mined-out area, compared with the result of multi-stage fuzzy synthetic judgment.Applying catastrophe theory and strength reduction method synthetically, the strength reduction method based on catastrophe theory is established to analyze the roof stability between multi-layer mined-out areas. Furthermore, the thesis creates two new concepts those are the safety factor of shearing and the safety factor of drawing crack to study the stability of complicated multi-layer mined-out areas. There are some useful conclusions:(1) Some conclusions about the roof stability between two-layer mined-out areas with different span and different roof thickness:for the purpose of the roofs with the same span, the thicker the roof is, the higher the safety factor of shearing is; for the purpose of the roofs with the same thickness, the wider the roof span is, the lower the safety factor of shearing is, and the lower the safety factor of drawing crack is. Nevertheless, the influence from the roof thickness to the safety factor of shearing has strong regularity, otherwise than the safety factor of drawing crack.(2) Analyzing the relation among the safety factor of shearing, the roof span and the roof thickness, fitting their interrelation with logarithmic function and getting the relationship formula.(3) Analyzing the influence from the ratio of thickness and span to the safety factor of shearing, and getting the following conclusions:the safety factor of shearing will increase along with the increasing of the ratio(v) of thickness and span. For the purpose of the roofs with the same ratio of thickness and span, the wider the roof span is, the lower the safety factor of shearing is; the smaller the roof span is, the higher the safety factor of shearing is.The thesis researches the stability of complicated multi-layer mined-out areas and the roof safety factor through making the mined-out areas in Gaofeng NO.105 mine body as a example. And the stability of areas are classified with the safety factor of shearing as yardstick when Fs=1.5. The result shows that it is the same as the classification results from multi-stage fuzzy synthetic judgment and rock mechanics analyzing. It also shows that the strength reduction method based on catastrophe theory has high accuracy to research the stability of complicated multi-layer mined-out areas. Finally, the advantages, the disadvantages and their applicability of existing treatment methods of mined-out areas are researched in detail. In addition, making the treatment of the mined-out areas in Gaofeng NO.105 mine body as a example, the thesis researches the treatment train of thoughts, the treatment project and the stoping technique from two aspect which are the stoping train of thoughts and the technique of underpinning pillar.