Study On Inclined Shaft Section's Excavation And Support Method Of Urban Expressway Tunnel

With the increasing traffic demand in urban areas and the requirement of building environment-friendly municipal facilities,a large number of underground roads have been built in urban areas of China.In addition to the characteristics of shallow burial,large span and low grade of surrounding rock,underground road tunnels often need to be constructed with inclined shaft,shaft and other structures to increase working face due to the requirement of construction period and the influence of length.Compared with the conventional tunnel section,the excavation of tunnel intersection is a three-dimensional problem,and the stress and deformation of surrounding rock and support are more complex.Therefore,how to control the large deformation or even damage caused by excavation is very important.In view of this,this paper takes Kangleyuan inclined shaft section of Shunhe Elevated Underground Road in Jinan City as an object,firstly analyzes its engineering characteristics and geological conditions,then studies the structural deformation and stress characteristics under different excavation conditions by using finite difference method,and finally evaluates the excavation and support effect of the tunnel combined with the monitoring data.The main research work carried out in this paper is as follows:(1)Analysis of the engineering characteristics and difficulties of inclined section.Combining with the investigation of relevant literature and similar projects,and the study of project characteristics(the site geological conditions,tunnel burial depth and clear distance,and the location relationship between main tunnel and inclined shaft),the characteristics and difficulties of the project are analyzed.(2)Three-dimensional numerical simulation analysis.Considering that it is difficult to analyze tunnel intersection by theoretical calculation a 3D numerical model is established to simulate the excavation and support construction process.The horizontal displacement value of pile top is taken as the safety evaluation index of foundation pit excavation and support,the vault settlement and surface settlement are taken as the safety evaluation index of the middle guide tunnel and the main tunnel section.The stability of foundation pit,middle guide tunnel and main tunnel section after excavation under different supporting conditions is determined.(3)Monitoring measurement analysis.The contents include the monitoring of foundation pit,deformation of middle guide tunnel and surface settlement.The characteristics of excavation and deformation of inclined shaft section are analyzed and the effect is evaluated.The results show that the surrounding rock of the intersection section of the tunnel is very complicated,and the excavation of the main tunnel is easily affected by the construction of adjacent tunnels.If the excavation and support are improper,it will easily lead to large settlement and deformation of the ground surface.The three numerical calculation and monitoring data show that the parameters of steel sheet pile,cast-in-place pile,leading pipe shed and initial support adopted in the middle and main tunnels of the foundation pit meet the requirements of tunnel excavation stability.The conclusions can provide some reference for similar projects.