Research On Support Measures For Bottom Structure Of Natural Caving Method Under Deep-buried Fractured Rock Mass

Most mining companies have stepped into the stage of deep mining with the depletion of shallow resources.The stability of mines where the natural caving method is used has always been the focus of attention because of the development of joints and fissures of the ore,the instability of the rock mass as well as the complexity of structures of plenty of tunnels at the bottom.After the deep mining,the rock mass conditions are particularly worse and faced with high stress.As a result,maintaining the stability of the bottom structure is extremely important for the effect of the natural caving method.According to the serious damage of the bottom structure and the failure of support in the deep mining area of a copper mine,the thesis analyses the stability of the bottom structure of the natural caving method during the process of advancing cutting by numerical simulation and explored the reason for the breakage of the bolt in the cracked roadway of the deep rock mass initially so as to propose a joint support scheme for the bottom structure.The main contents of the research are as follows:(1)The rock mass quality classification and mechanical parameters of the mining area to be studied are determined by investigating the engineering geology of the mining area,and the geostress law of the mining area is analyzed.(2)It is concluded that the tensile stress at the majority of the roadway and the intersection of the peach-shaped pillar and the ore level exceeds the rock mass after the bottom is pulled by using Midas-GTS software to study the influence of the advancing cutting on the stability of the bottom structure.At this time,these parts need to be supported.(3)The model is simplified when constructing the 3D model of the bottom structure because of the complexity of the structure.The Phase2 finite element software is used to analyze the influence of the simplified roadway model on the bottom structure.The simplification of the roadway shape is not enough to affect the three-dimensional overall numerical results.(4)The ANSYS software is used to construct the anchored rock mass,and the influence of the modulus ratio of the rock and the anchor on the stress deformation characteristics and the yield fracture failure mode of the anchor is studied.The conclusion is that when the ratio of the the elastic modulus of the rock mass and the elastic mode of the anchor amount is greater than 0.17,the yield form of the bolt in the jointed rock block is dominated by shear stress.At this time,the design strength of the bolt in the roadway should be determined according to the shear strength.(5)A joint support scheme for the bottom structure of the natural caving method without tension is adopted based on the analysis of the original support form and the cause of failure of the mine.This support scheme works well according to numerical simulation and field application.