Studies On The Consolidation Behavior Of Soft Soil Around A Circular Tunnel And The Interaction Theory

It is well known that the changes of internal force and deformation associated with a tunnel in soft soil will last for a long time due to the consolidation and creep of the soft soil as well as the partially permeable characteristics of the liner of the tunnel. However, the relevant theoretical study lags far behind the engineering practice. To understand and master the influence of the partially permeable characteristics of the liner, the consolidation and creep of soft soil on the internal force and the deformation of the tunnel so as to provide some technical supports for the design of the tunnel and the practice engineering, in this dissertation, the consolidation of soft soil containing a circular tunnel and the dynamic response of the tunnel subjected to the external loading are systematically studied on the basis of Biot's theory of consolidation. The main original work includes:1. Considering the permeability of lining and assuming that the tunnel is partially sealed with partial drainage boundary and the lining is thin and flexible, the consolidation of a deeply embedded circular tunnel in viscoelastic saturated soil is studied, in the Laplace domain. By disassembling the stress and pore pressure boundary conditions of tunnel so that the consolidation of tunnel can be decomposed into three simple computational model, the corresponding solutions are derived in Lapalce transform domain respectively, and the solutions of consolidation of tunnel can obtained by assembling the components of three simple models. The available solutions without considering the consolidation and creep of clay, the permeable and impermeable boundary of tunnel are just extreme cases of this paper. Numerical results obtained by inverting Laplace transform are used to analyze the influence of damping coefficient of clay, parameter of partial permeability and coefficient of lateral pressure on the consolidation of tunnel.2. Utilizing the theory of thin shell, the interaction of soil-structure of a partially sealed circular tunnel in viscoelastic saturated clay is investigated by considering the property of creep of lining and clay, and the stiffness of lining. The solutions of consolidation and creep of tunnel are obtained in the Laplace transformation, and they can be degraded to the solutions without considering the stiffness of lining, that is, the liner is flexible. Numerical results in time domain are obtained by applying the technique of inverse Laplace transformation to the consolidation solution of interaction of soil-structure and are used to discuss the influence of damping ratio of lining to clay, relative stiffness and thickness of lining and clay, parameter of partial permeability and coefficient of lateral pressure on the interaction of soil-structure. At last, the result obtained in this paper is compared with the available solution. It is shown that there is great influence of the stiffness coefficient a0 revealed by the stiffness of liner and clay. The values of bending moment of tunnel increases with the increasing of a0. In the range of 1-100, a little change of a0 can arose an obviousdifference of bending moment.3. The consolidation and interaction of soil-structure of a partially sealed pressure tunnel under symmetrical loading and fluid pressure are considered. The thick cylinder, the concentrative drainage and the impermeable barrier cases are analyzed under the conditions of considering (with lining) and without considering (no lining) the time-dependent of pore pressure. The corresponding solutions to three cases are obtained and are used to analyze the influences of parameter of partial permeability. A stress coefficient defined from the porosity of lining material is proposed to ascertain the value of interior water pressure that supported by the lining material and pore water, respectively, which matches the computation of pressure tunnel with the practical case. As a result, two extreme assumptions that the boundary of tunnel is permeable or impermeable during the calculation can be avoided.4.