Research On Risk Of Deep Foundation Pit Supporting Urban Subway Based On FLAC3D

The process of urban modernization is speeding up,and the central buildings in the city are not only developing to a higher direction,but also to a deeper direction.As one of the symbols of urban modernization,subway can relieve the ground traffic pressure.Because of the long construction period and complex surrounding environment,there are often some accidents in the construction process of subway deep foundation pit engineering,which cause huge loss of life and property and bad public opinion.In this paper,based on the foundation pit of Sanyuan station of Chengdu Metro,FLAC3 D numerical simulation is used to study the foundation theory of deep foundation pit engineering,and the retaining structure,surface settlement and pit bottom uplift deformation are obtained.This paper collected 110 subway construction collapse accidents,92 of which had detailed reasons,which provided relevant basis for the determination of risk level.(1)Through the study of the theory of deep foundation pit,deep foundation pit engineering is a complex engineering,related to multiple disciplines,greatly affected by the surrounding environment,comprehensive complex.In this paper,the commonly used retaining and supporting structure of deep foundation pit engineering and the failure form of foundation pit are described.(2)Based on the engineering case,through FLAC3 D finite difference software,the steel pipe internal support model of diaphragm wall of deep foundation pit is established,and the horizontal deformation of deep foundation pit,the deformation of retaining structure and the uplift of pit bottom are analyzed in detail.According to the analysis of the calculation results,with the increase of the excavation depth of the deep foundation pit,the heave of the pit bottom is larger,and the maximum horizontal deformation of the retaining structure occurs near the corner of the pit.With the increase of the excavation depth,the maximum horizontal displacement moves down,from the initial linear law to the parabolic law,and the maximum horizontal displacement occurs near the foundation pit.With the distance from the pit edge getting farther,the horizontal displacement decreases.It is close to 0.(3)This paper collects 110 subway construction collapse accidents,92 of which have detailed reasons,and makes a comprehensive analysis of the characteristics and laws of the accidents.The fuzzy comprehensive evaluation method is used to analyze the risk of deep foundation pit support,and the deformation of retaining structure,surrounding soil and pit bottom simulated by numerical simulation are taken as the first level risk index factors.The risk analysis model of support structure is established,and the risk factors are scored according to the frequency of accident inducements,and the risk level is further evaluated.It is concluded that the risk of this model is at low level.