Research On Key Construction Technology Of Shallow Tunnel Under High Grade Highway

In recent decades,China’s national economy has been developing rapidly,and the national economic strength has been significantly improved.On this basis,China will advance towards the goal of a modern country.This puts forward higher requirements for the infrastructure construction of our country.To speed up the construction of socialist transportation modernization power is the first technical field to speed up the construction of socialist modern economic management system.Due to the formation of the overall traffic network and the continuous development and expansion,it is more and more important to build shallow tunnels under high-grade highways.Therefore,it is necessary to study the safety of Underpass tunnels.In this paper,on the basis of summarizing the existing research results of highway or building underpass tunnel,starting from the selection of excavation mode,determination of blasting scheme and reasonable lining support means,combined with the actual engineering situation of Fenghuang road tunnel,the finite element software MIDAS /gtsnx is used to carry out three-dimensional modeling for the underpass section of Fenghuang road tunnel under various working conditions Finally,the accuracy of the numerical simulation is ensured by comparing the field monitoring results.It can deepen the understanding of safety construction of shallow tunnel under high-grade highway,and provide reference for similar engineering and revision of design and construction specifications in the future.Under the same conditions of tunnel surrounding rock,different excavation sequence and support steps will cause different redistribution of surrounding rock stress.Midas / GTS NX is used to inspect the tunnels under the main line of the South East extension expressway of the Second Ring Road(i.e.the mileage stake number is K0 + 140.00)～ K0 + 154.27)modeling,3D dynamic numerical simulation of the whole process of excavation and support of upperbench CD method excavation and bench method excavation is carried out.The different influences of different excavation methods on the stability of surrounding rock and initial support characteristics of the main line under the South East extension expressway of the Second Ring Road are discussed.The calculation results are combined with the actual situation,and the accuracy of the calculation results is verified by the actual engineering monitoring results Certainty.It can be concluded that under the working condition of Fenghuang road tunnel,the vertical settlement of surrounding rock caused by CD excavation is smaller,the disturbance to the upstream highway is smaller,and the safety and economy are higher.In the case of tunnel excavation,the vertical displacement caused by the bolt in the excavation process is significantly lower than that in the case of tunnel excavation without bolt,and the results show that the displacement caused by the bolt in the excavation process is significantly lower than that in the case of tunnel excavation without bolt.It is confirmed that the disturbance to surrounding rock mass and up high-grade highway can be effectively reduced by strengthening support,so as to achieve the purpose of not blocking the normal operation of the upward highway.Through the analysis of the monitoring results of Fenghuang road tunnel blasting,the necessity of monitoring is concluded.In response to the impact of blasting on surrounding rock mass,different preventive measures should be selected;at the same time,combined with the actual blasting situation of Fenghuang road tunnel,the blasting monitoring measurement under class IV Special surrounding rock environment is discussed and analyzed to determine the reasonable blasting mode of tunnel under the crossing section.The specific method is bench excavation.The upper bench of the tunnel is excavated by CD method,and the cantilever roadheader is used for excavation.The cyclic footage is 1.5m,and the drilling and blasting method is selected for the construction of the lower bench,and the blasting footage is1.5m.The vibration velocity amplitude measured by this method is within the standard range,which can ensure the safety and economy in the process of tunnel construction.Through the analysis of the monitoring and measurement results of chejiaoshan tunnel,the change information of surrounding rock and support system during the construction process is obtained;the monitoring and measurement data of the tunnel Undercrossing sectionare analyzed to determine the key monitoring period in the excavation process of Fenghuang road tunnel,and timely feedback analysis is made.The necessity of monitoring is concluded,and according to the feedback of monitoring results,in the actual construction process of the tunnel,there is no instability of surrounding rock and no damage and cracking of the road above,which verifies the accuracy of the numerical simulation calculation and the feasibility of the excavation and support method.