Research On Deformation Control And Construction Method Of Advanced Supporting Surrounding Rock In Soft Rock Section Of Tunnel Opening

The entrance section of highway tunnels is mostly in soft rock formations.For construction safety and early entry,it is often necessary to adopt advanced support and reasonable construction methods to control the deformation of surrounding rock at the entrance section and ensure the stability of the surrounding rock.Taking the entrance section of a highway tunnel in Sichuan as the background project,through theoretical analysis,on-site monitoring and numerical simulation,the deformation control measures and reasonable construction methods of the surrounding rock of the tunnel entrance soft rock section are studied.The main conclusions are drawn:(1)The main area of surrounding rock settlement is mainly concentrated in the vault of the cave,and the area with large stress changes is mainly concentrated in the surrounding rock area of the vault,the arch foot of the tunnel and the inverting arch area;the reinforced grouting circle with long pipe roof is effectively formed The "pressure-bearing arch"concentrates the plastic zone of the surrounding rock at the arch foot;the influence of the palm shed axial force and bending moment distribution on the palm face is mainly within about 3 excavation feet before and after the palm face excavation.(2)The on-site monitoring data is analyzed to determine that the surrounding rock deformation of the soft rock section of the tunnel entrance can be divided into three stages:the early rapid deformation stage,the middle slow deformation stage and the later stable deformation stage.Comparing and analyzing the numerical simulation calculation results of the vault settlement and horizontal convergence displacement with the on-site monitoring results,the deformation of the two is basically the same,which verifies that the numerical simulation is true and reliable.(3)Under the condition of advanced support of pipe shed and small pipe,the tunnel wall rock deformation with different values of the three main parameters of pipe shed ring spacing,pipe diameter and pipe length are compared,and the numerical simulation results show that the pipe shed ring spacing is reasonable The value is 40cm,the reasonable value of the pipe diameter is 108mm and 159mm,and the reasonable value of the layout length is 30-40m.(4)With the advance support of pipe shed and small pipe,the two methods of single-wall guide pit method and annular excavation core soil method are numerically calculated to obtain the settlement of the vault and the horizontal displacement of the side wall under the two methods.,Surface subsidence,surrounding rock stress and plastic zone distribution range change law,the numerical simulation results show that the deformation control effect of the single-wall guide pit method is better than the ring excavation core soil method,and the single-side guide pit is determined Method is the preferred method of excavation for such tunnels.