Face Stability And Deformation Of Shield Tunneling In Sandy Silt Soil

The shield tunneling method, as one of the main construction methods of metro tunneling, has been used widely in China. The safety control of excavation face and variation of soil environment induced by shield tunneling is the main issue during shield tunnel design and construction. Because the property of sandy silt is usually between that of sand and that of clay, it is hard for engineers to understand the engineering property of sandy silt during shield tunneling. The main research contents are as follows:(1) Relevant in-situ measurement is executed during Hangzhou metro tunneling in sandy silt. From the results, it is concluded that variation of pore pressure against distance is a Zigzag-shape distribution against distance. The latter shield tunneling has thrust influence on earlier shield tunneling, and reasonable grouting helps to control soil deformation around shield tunnel.(2) The interaction between soil and shield is analyzed. The formulation of soil deformation induced by torque between soil and cutterhead is obtained derived from Mindlin solution which could verify the phenomenon that the settlement trough is assymmetric. By revising formulation of soil deformation induced by soil loss, the total formulation of soil deformation is obtained which is useful in construction stage.(3) A three-dimensional fast Lagrangian differential finite element method is used to simulate the deformation and failure of excavation face considering the influence of ground water. The limited face pressure of excavation face is obtained by a great deal of analysis, and the influence of tunnel depth, the depth of ground level, time of shield stopping and soil property is also analyzed by using numerical model.In this thesis, the variation regularity of soil stress and deformation induced by parallel shield tunneling is concluded by field measurements, and surface settlement is analyzed by formulation derived from Mindlin solution, and the set range of face pressure in sandy silt is obtained by numerical analysis. All of the conclusions provide some relevant suggestion for shield tunneling in sandy silt.