Research On Long-term Nonlinear Consolidation Deformation Of Shield Tunnel In Soft Soil

Many theoretical and field studies have been performed on tunneling induced response of surrounding soil and interaction of soil-structure, yet most of these studies are concerned with short-term response by tunnel construction. However, many field measurements comfirmed that long-term deformation of surrounding soft soil of shield tunnels could be very large and last for a long time after construction, and the longitudinal settlement of shield tunnel is uneven. In the various factors that affect the long-term settlement of metro tunnel, the initial excess pore pressure induced by tunneling, partially sealed lining, and relative permeability of soil-lining are more significant. Meanwhile, for shield tunnel buried in deep soft soil, train loading during long-term operation after construction could induce the variation of stress, strain, and pore pressure, leading to reduction of soil stiffness, enlarging of soil deformation. In this dissertation, steady seepage state, dissipation of excess pore pressure, and land subsidence of soil around shield tunnel are systematically studied by both analytical method and field study. The main original work of this dissertation includes:1. The empirical e-lg ?' and e-lg k relation are introduced to simulate nonlinear behavior of soil during long-term consolidation. Then based on the free strain assumption and continuity equation, the governing equation of two-dimensional nonlinear consolidation of soil around shield tunnel is derived.2. The linings of shield tunnel are idealized as completely permeable or completely impermeable, which represents the upper and lower limits of the induced soil consolidation behavior. Then the partial sealed linings of tunnel are idealized as a homogeneous body by introducing a relative parameter of soil-lining permeability ? which is first proposed by Li(1999). The analytical solutions of governing equation of nonlinear consolidation are derived by introducing the partially permeable condition ? to discuss the influence on soil consolidation, dissipation of excess pore pressure, and long-term consolidation settlement.3. The train loading is simplified as equivalent rectangular cyclic loading q to obtain the analytical solution of nonlinear consolidation of soil around shield tunnel with both idealized sealed linings and partially sealed linings. By the adjusting of equivalent rectangular cyclic loading and relative parameter of soil-lining permeability, the influence of train loading and coupled effects of both partially sealed lining and train loading on soil consolidation, ground settlement, and settlement rate are discussed.4. Merchant model is employed to simulate the visco-elastic deformation of soil, and the governing equation of consolidation of visco-elastic soil around shield tunnel with partially sealed linings is established. Then a recursive method is used to introduce e-lg k relation to consider the variation of soil permeability during consolidation. The analytical solution of long-term ground settlement of shield tunnel in creep soil under train loading is obtained.5. Three case studies from Shanghai metro line No.l and No.2are simulated to investigate the behavior of nonlinear consolidation of soil around shield tunnel. The rationality of analytical solutions of nonlinear consolidation and visco-elastic model are verified by the comparison between predicted and observed long-term settlements?...