Construction Monitoring And Risk Assessment For Large Cross-Section Tunnels Of Urban Subway

The construction of subway has become a symbol of the rapid urban development.Large cross-section tunnels are constantly emerging with the development tendency of the subway construction with “higher,bigger,wider and shallower”.In order to improve the convenience,the appearances of up and down crossing tunnels are inevitable,which enlarge the interaction among the existing tunnels and newly-built.The study on the large cross sectional tunnels and the interactions among adjacent ones is of vital importance in underground engineering research.This paper is based on the background of the proximate large cross-section tunnels of the first-stage project of Harbin Metro between “Harbin south station to Academy of Agricultural Sciences station”.During the construction process,we not only had monitored the deformation of the tunnel surrounding rock and had a numerical simulation but also estimated the construction risk.The main research contents are as follows:(1)From the on-site monitoring data,the variations of the surface subsidence,the dome subsidence and horizontal convergence were obtained and analyzed.The results show the ground settlement has a certain regularity which accords with the Peck settlement curve.It is found that the subsidence of the dome and the ground surface is consistent.The final subsidence of the first excavated hole is the largest,which indicates that the excavation of other holes has a certain impact on the subsidence of the first excavated hole.(2)Taking the ANSYS software to have a numerical simulation of the both side heading method of large cross-section tunnels during the construction process,and analyzing the stress change state and the displacement of soil mass and primary support during the dig of pilot tunnel.The research shows that the variation of displacement of ground surface,arch crown settlement and horizontal convergence are the biggest caused by digging the upper middle pilot drift.(3)Through the on-site risk identification,it shows that the influence among adjacent tunnels is a key topic in the construction risk assessment.Therefore,the Kent index method and fuzzy mathematics method were respectively adopted to perform the risk analysis,and the calculated risk level is both moderate,which infers that they are consistent.