Research On Segment Structure Of Under River Shield Tunnel With Large Diameter And Its Engineering Application

As an effective measure to mitigate the dilemma between the limitation of overground spaces and the heavy load of transportation, large shield tunnels become important underground structures in urban area owing to the breakthroughs in construction technology. Compared with the quick development in practical engineering, the theoretical research in structural model for large shield tunnels is relative delayed. Currently, those designing methods for small shield tunnels are simply applied when designing large tunnels. Considering the structural specialties in large shield tunnels, a detail study on the designing method for large shield tunnels is presented in this thesis. The major points of the author's work are as follows:First, starting from predecessor's research, based on the Biot consolidation theory, on account of dynamic change of porosity and permeability, an expansion model was established, which could simulate the coupling effect of time-dependent stress-strain behavior of soil and seepage effects of groundwater. The calculator program of the model was compiled with the FORTRAN language.Secondly, the basic theory and method calculating external pressure are studied systematically. Applying the FEM, considering the coupling effect of time-dependent stress-strain behavior of soil and seepage effects of groundwater, combing the engineering example, and through the finite element simulation and analysis, the pressure model of the soil around the tunnels is acquired.Thirdly, basing on the test data of load cushion and water-proof plastic , the joint's mechanical characteristic has been analyzed and the nonlinear relation between the segment joint stiffness and joint's internal force has also been obtained. In order to make convenient application for engineering, the dissertation has established a joint stiffness model for shield segment joints and a corresponding joint program is written.Fourthly, 3D Numerical model of continuous soil-Shell-spring is presented so as to analyze the 3D member forces of the segmental linings of shield tunnel. With the application of FEM, the model employs several types of elements, such as thick shell, GOODMAN, contact and solid elements, and concerns with the extrusion between segments in the joints, the stiffness contribution of joints, the cooperation between segments and surrounding soil.Finally, based on 3D Numerical model of continuous soil-Shell-spring, the internal forces and displacements of continuous-jointed segmental lining and stagger-jointed segmental lining are computed separately for the tunnel engineering of shanghai-Chongming. The result of this dissertation will be provided to the staking company for working reference.