Research On The Long-term Behavior Of Sheild Tunnel With Partially Sealed Linings In Soft Soil

Tunnelling in soft ground is an increasing commonly geotechnical activity for construction of urban transportation in many cities around the world due to recent city developments. However it has been shown from a lot of shield tunnels in soft soil that the long-term settlement is significant. Its unfavorable influence on tunnel structure, waterproofing of joints and normal running of a tunnel is more and more serious. Consequently, prediction of long-term settlement of shield tunnel becomes an important engineering issue to ensure the safety of an existing tunnel.There are lots of components affecting the long-term settlement of tunnel in soft clay including the magnitude and distribution of excess pore pressure around tunnel due to shield tunneling, the drainage condition of linings, the vibration damage of the vehicle to the surrounding soils, the time-dependent stress-strain behaviour of soils and so on. However the relevant theoretical research lags far behind the engineering practice. To understand and master the influence of the partially permeable characteristics of linings, the consolidation and creep of soft soil on the internal force and deformation of the tunnel, the long-term behavior of shield tunnel is systematically studied using both analytical and numerical methods in this dissertation. The main original work includes:1. Considering the partially sealed tunnel boundary, an analytical solution for the consolidation of tunnel in viscoelastic saturated soil is proposed. Based on the linear rheological model of three units and Terzaghi-Rendulic consolidation theory, the governing equation about excess pore pressure is established with parial drainage boundary. The excess pore pressure as well as the volume strain can be determined atany time of any position in the considered region. Finally, the vertical strain can be separated from volume strain and the settlement of tunnel can be derived by integration of vertical strain of the compressible layer.2. The long-term settlement of metro line NO. 1 in Shanghai is predicted based on the analytical solution. A satisfaction agreement is obtained although errors exist between the predicted results and field monitoring data. Meanwhile, the influence of parameter on the long-term settlement of tunnel is analyzed, such as coefficient of permeability of the lining and soil, damping coefficient of soil.3. Using the FDM code—FLAC, the long-term behavior of sheild tunnel is simulated. A visco-plastic constitutive is implemented in the code coupled with Biot's consolidation theory. The multi-layered characteristics of soil are also taken into account. A multiple-step numerical procedure is designed to simulate the mechanical behavior of shield tunnel in different period during the long-term duration. Finally, the long-term reponse of shield tunnel can be numerically predicted.4. The predicted long-term settlements of numerical method are compared with field monitoring data and the analytical solution. It shows that the results of numerical method can reflect the law of evolution of long-term settlement well. The influence of parameter on the long-term settlement is analyzed and their difference with the analytical solution is also interpreted. The two adopted methods are validated and can provide technical supports for design of tunnel and practice engineering.