Analysis Of The Effect On The Safety Of Deep And Large Foundation Pit Excavation On Metro Tunnel

With the accelerated process of urbanization in recent years, the construction of the urban rail traffic is developing rapidly, there are beginning to build subways, light rails and other new modes of transportation massively in the provincial capital.There are some new problem because of the land for urban construction gets tense: if the deep foundation pit excavation of a pit is close to the existing subway tunnels, unloading of the deep foundation pit excavation can change the stress field and displacement field of surrounding rocks of subways, in addition, it?s has an impact on the existing subway tunnels and the surrounding buildings,or even cause serious damage to the structures of the subways and significant economic losses and security incidents.However, the city subway tunnels are extremely strict to the deformation, the additional stress and the bending moment, therefore it has the significant influence to the nearby subway tunnels and the surrounding environment that the foundation pit excavation is proper or not.Safety analysis and monitoring of the progress of the construction must be carried out in order to ensure the normal operation of the subway structures and the safety of the surrounding buildings.Accordingly,It has theoretical significance and practical value to analyze the influence of excavation on the adjacent subway structures accurately that can ensure the stability and durability of the structure of the subway tunnels.In order to analyze the influence of excavation on the safety of adjacent metro tunnel, this paper takes the construction of the two stage excavation engineering of a nearby subway tunnel in Guangzhou as the background, and uses the method of numerical simulation.The main research contents and results are as follows:(1)According to the mechanism of the motion of the surrounding surface and the calculation theory of the lateral displacement and ground settlement, it has an analysis about the lateral displacement, ground subsidence and heave of the retaining structure during the excavation of the deep foundation pit.(2)The foundation pit, the ground subsidence and the subway tunnels are modeled as a whole by Midas and other finite element software.Firstly, the numerical simulation results of the foundation pit are compared with the original site of the monitoring results,and according to the results of the comparison, it can be seen that the finite element results are the same as the monitoring data, which proves the correctness of the model from the side.Secondly,using MIDAS/GTS to simulate the process of excavation of the foundation pit,and analysis the influence on the lining structure deformation, additional stress and bending moment of the construction of the subway tunnels during the excavation of the deep foundation pit.Finally,it changes the level of the underground water,and analysis the influence of the construction on the structure deformation, additional stress and bending moment of the subway tunnels.(3)Based on the theoretical analysis and finite element analysis, this paper puts forward the protection measures and suggestions for the safety of the subway tunnels in Guangzhou.