| With the implementation of the western development strategy,it is often necessary to build tunnels in karst areas.The existing design method of supporting structure of karst tunnel mainly refers to the experience of similar projects.The supporting parameters are greatly influenced by the designer,which may become a potential safety hazard in the design and construction of karst tunnel.Based on the rongjiawan karst development tunnel project of Zhengzhou Wanzhou high speed railway,the surrounding rock pressure calculation and support parameter optimization design of the exposed karst tunnel are carried out by using the methods of theoretical analysis and numerical simulation.The main research contents and conclusions of this paper include:(1)Combined with theoretical analysis and numerical simulation,an improved method of initial stress state of karst stratum is proposed,which is suitable for numerical simulation of karst tunnel.This method solves the problem that the traditional method of initial stress state of stratum is difficult to simulate the real stress distribution of karst tunnel wall.(2)The numerical calculation method of tunnel surrounding rock pressure considering the tensile strength characteristics of surrounding rock is established,the distribution characteristics of surrounding rock secondary stress and blasting damage during tunnel construction under the influence of exposed empty karst cave are analyzed,and the influence law of exposed empty karst cave at different positions and sizes on tunnel surrounding rock pressure is proved.The results show that the exposed empty karst cave will lead to the obvious increase of surrounding rock pressure,and the surrounding rock pressure increases first and then decreases with the increase of karst cave area.During the design of tunnel support structure in exposed Karst Section,the calculated value of surrounding rock pressure should be corrected.(3)A three-dimensional numerical model of karst tunnel considering blasting damage effect of surrounding rock is established,and the longitudinal influence range of exposed karst tunnel on tunnel surrounding rock pressure is revealed.The displacement of surrounding rock and the stress characteristics of supporting structure under the influence of exposed empty karst cave are studied,and the optimization scheme of tunnel support in Karst Section is put forward.The results show that the longitudinal influence range of the exposed empty karst cave on the surrounding rock pressure is about 2.25 times the diameter of the karst cave from the center of the karst cave,and the surrounding rock pressure in this range is significantly higher than that in the non karst cave section.Within the influence range of karst cave,increasing the thickness of shotcrete and steel support parameters in the initial support structure can significantly improve the deformation of surrounding rock and the stress state of the support structure,and provide guarantee for the safe construction of the tunnel.104 figures,20 tables and 112 references... |
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