Optimization Study On Initial Support Parameters Of Soft Surrounding Rock Tunnels

With the rapid development of China's economy,the development of tunnel engineering has made a breakthrough,however,our country is not fully grasp the advanced technology of the tunnel technology power,for different conditions of the tunnel project,we still need to rely on the accumulated experience.The new excavation of the tunnel generally use the initial support to protect the new excavation of the airport surface and prevent the deformation and destruction of the surrounding rock of the sustainable development.The initial support can limit the deformation of surrounding rock,improve the stability and bearing capacity of surrounding rock,but the research on the form and parameters of the tunnel support and support in weak rock still can not keep up with the actual needs of the project.This paper is based on the project of a tunnel in Guizhou,which is a weak surrounding rock,the surrounding rock is not developed.In this paper,based on a tunnel of Biwei high speedin Guizhou,the parameters of the initial support in weak surrounding rock are studied,and the parameters are also selected according to the calculation results.Concrete results are as follows:(1)Lithology,rock mass structure and fracture,stress,engineering factor are the factors that affect the stability of tunnel under soft rock.And the failure characteristics of the tunnel under the weak surrounding rock include various forms of damage,large deformation,high deformation speed,long duration,large damage range anddifferentpositions.The mode of failure includes the block,expansion,extrusion,sliding and so on.(2)2.5m,3.0m,3.5m,4.0m,4.5m five operating conditions are calculated by using the finite element software MIDAS/GTS.By comparison,the change of the value of the 3m~4.5m is very small,and the length of the anchor is very small,so the 3M is the best value of the length of this project.(3)0.8m,1.0m,1.5m,1.2m four kinds of working conditions are calculated by using the finite element software MIDAS/GTS.The results show that the layout of the anchor after 1m has obvious influence on the displacement of the lateral wall and the impact of the drum,and the 1m spacing is the best.(4)On the steel arch models take 14,18,22 b three working conditions are calculated by the finite element software MIDAS / GTS,the comparative analysis of surrounding rock stress field,surrounding rock displacement,axial force of bolt,jet concrete axial force and bending moment.By calculation,the displacement of surrounding rock,the axial force of bolt,and the axial force of the injection of concrete are the least.But from economic considerations,selection of industry No.18 steel arch as the engineering optimization of arch model.(5)For the monitoring of the tunnel construction,the measurement results and the priority of the calculation results are compared.The results of the finite element calculation are more than those of the monitoring and measurement.The simulation results of the finite element method are the same as the actual measurement data.The consistency of the two trends is verified,and the feasibility of the finite element simulation is verified.