Numerical Analysis Of Excavation Method And Support Optimization Of Large-section Ⅲ-level Surrounding Rock Tunnel

China has stepped up its efforts to build infrastructure,tunnel projects are also on the rise,however,the section types,geological conditions and environmental factors of railway tunnels are complicated,and the accidents caused by them are endless.Therefore,it is urgent to determine the reasonable,safe and economical construction methods,excavation dimensions and support parameters.This paper is based on the level 3 surrounding rock Bai Yang Lin railway tunnel.The finite element software MIDAS/GTS was used to make modeling analysis.The stress,strain,displacement of surrounding rock and stress,strain characteristics of support under different design parameters are calculated.Through analysing their changing characteristics to confirm the reasonable excavation method,reasonable excavation step and reasonable support parameters.The main work of this paper is as follows.(1)A reasonable numerical model is established with some parameters about the level 3 surrounding rock railway tunnel,and the construction simulation of different construction methods are carried out about the tunnel excavation,and the ideal construction method is determined.(2)By establishing the model of tunnel,the length of tunnel excavation is simulated,then analyzing the different excavation step length of the effects about the supporting structure and the level 3 surrounding rock’s stress,strain and displacement,then determine the ideal excavation step length.(3)Four support schemes are proposed to analyze the influence of different support schemes on the stress,strain and displacement of surrounding rock.(4)The influence of five kinds of bolt diameter on the stress,strain and displacement of the tunnel surrounding rock,and the mechanical influence of shotcrete and bolt,determine the reasonable diameter of bolt.(5)The effects of five bolt lengths on the stress,strain and displacement of the tunnel surrounding rock,and the mechanical influence of shotcrete and bolt,determine the reasonable length of bolt.(6)The influence of four kinds of shotcrete thickness on the stress,strain and displacement of the surrounding rock,and the mechanical influence of shotcrete and bolt,determine the reasonable thickness of shotcrete.