The Theoretical Study And Numerical Simulation Of Ground Subsidence Caused By Shield Tunnel Excavation In Soft Soils

Tunnel construction technology with shield driven method is an advanced one used in infrastructure and is a common tunnel excavation method of metro subway in soft soils because of the unique characteristics and advantages of quickness, goodness, economy and safety, et al. But it is inevitable to cause some environmental and geotechnical problems during the shield excavation process, especially the problem of ground subsidence. This will affect the normal use and the safely running of the shield tunnel and the ground surface building and underground facilities if the ground settlement is too much. People still lack enough knowledge and engineering experience on the causes of soft soil moving and ground settlement during shield moving forward. Hence, it has important theoretical and engineering practice significance to reduce the effect of shield excavation on the disturbance of soils around the tunnel and the effect on the surface buildings and underground pipelines, and to study the causes and mechanisms of stratum moving and ground subsidence during the process of shield tunnel excavation.Based on the research results obtained and taken the excavation of the subway certain tunnel section of Hangzhou Metro Subway Line #1 for example, the numerical simulation and theoretical analysis is made of the excavation process of the earth pressure balance type shield excavation using the 3-D nonlinear finite element software ADINA. The main contents of this paper can be summarized as follows:(1) A brief introduction is made on the problem of ground subsidence caused by tunnel shield excavation, and the research status and results obtained at home and abroad of the ground settlement by tunnel excavation.(2) A brief introduction is made on the engineering properties of soft soils and the shield excavation method commonly used in the soft soil layer– a balance of earth pressure type shield excavation. Then, based on the engineering properties of soft soils, it is analyzed of the characteristics, developing process and the settlement deformation mechanism caused by tunnel shield in soft soils.(3) Firstly, the analytical formulae of the ground transverse subsidence proposed by Sagaseta are simplified into the plane strain analytical formulae. After amendment, the formulae for the ground transverse subsidence are gotten and the results obtained by the analytical formulae are compared and analyzed with several field testing results at home and abroad, which indicates that they agree very well. Finally, the ground transverse subsidence curves of certain tunnel section of Hangzhou Metro Subway Line #1 are predicted in advance.(4) The changing law is obtained of the transverse and longitudinal ground subsidence and strata settlement at different depth after excavation of tunnel shield, using the FE numerical simulation of certain tunnel section of Hangzhou Metro Subway Line #1 and the analysis of the calculation results.(5) Using the numerical simulation method of finite element, the effect is analyzed on the ground subsidence of tunnel's relative buried depth, the mechanical parameters of soils, the materials of shield lining and back grouting, et al., and is revealed by changing the values of different parameters in turn.