Study On Construction Mechanics Subsurface Excavation Of Hongqihegou Large Station

With the accelerating urbanization process and the urban population dramatic increasing in China,the traffic congestion and other problems that it brings about gradually become the most important issue to block urban development and affect people’s daily lives.In order to reduce ground traffic pressure, the full use of underground space becomes a tendency in future, So there will be more and more large section underground excavation projects.Although several large cross section station has been built and accumulated some experience, large cross section station still needs further in-depth research,It is so as to provide follow-up new construction guidance and reference.This paper relies on Hongqihegou station of CRT Line three in Chongqi, employs survey literature, numerical simulation,field experiments,carries out research on construction mechanics of shallow excavation large section tunnel likes Hongqihegou station.the main content as follow:(1) Collect a lot of information about large section tunnel construction and research at home and abroad. Clear the lack of construction and development trend of the domestic large cross section of shallow tunnels. Accord to Hongqihegou station project,define the research purposes and direction.(2) Introduce controlling ultimate displacement standard of surface subsidence and evaluating rock yield approach index. The ultimate displacement of Hongqihegou station surface subsidence is72mm. Yield approach index can be used to evaluate the degree of rock yield during excavation.(3) Base on the feature of Hongqihegou station,bring forword two methods of construction which is suitable for the station. Compare the numerical results, multi-heading excavation is suitable for this project.(4) Compare the numerical simulation with monitoring measurement,the character of displacement and stress of rock and structure during construction with multi-heading excavation as follow:①The surface and arch subsidence have the similar discipline,the single heading excavation affect little on settlement and core top level do most.the middle rock beam act on limiting the transverse displacement of rock,the main transverse displacement accur after the rock beam removed.②The step effect little on the stress of rock which is still covered.the stress have small change after single heading excavation.when the rock beam removed,the tensile stress reduce and compressive stress increase in middle wall. The arch area stress redistribute after core top level removed.the tensile stress become major in the arch.the compressive stress increase in skewback and wall feet.③The depth of rock stress effected by excavation is about twenty meter below the middle wall.for the case of shallow,the arch rock is turbulent that the frist principal stress change a lot and third principal stress vary little.④The rock is not yield during excavation and the straight wall of lower heading and core rock column is approach to yield elavated by Yield approach index,so more support and monitor is needed during excavation.(5) Monitoring measurement is a important method for NASN,it can provide the reliable date for researching on the character of Hongqihegou structure and enriching the design theory of the similar tunnel. According to the date of monitoring measurement,we can get the decipline of surface subsidence,transerve,initial lining and verificate the result of the numerical simuliation.it can be referred to other similar project.