Research On Key Issues Of Segmental Lining Structure Design For Underwater Shield Tunnel With Large Cross-Section

Currently, China is in the period of rapid development for constructing underwater tunnel and in demand of national economic development, a large number of underwater tunnels have been started construction. Most part of these tunnels are constructed using shield tunneling method. However, facing the challenges of complex underwater geological environment and the large-scale tunnel structures, the existing design methods, theories or experience for designing structures of shield tunnel could not be applied appropriately. Therefore, to consummate the structure design methods of large underwater shield tunnel, and ensure the safety, economy, reasonabllity, and durability has become a key issue to be solved urgently. In view of this, several key issues for designing the segmental lining sructures for large underwater shield tunnels are studied in this paper, and the results will have important practical significance.Based on several large underwater shield tunnels whose design were presided by author, such as Guangzhou-Shenzhen-Hong Kong High-speed railway Guangzhou Shiziyang Tunnel, Nanjing Changjiang Tunnel, Wuhan Changjiang Tunnel, Wuhan Sanyang-road Tunnel etc., and supported by the National High-Tech Research and Development Program of China (863 Program):’Research on mechanical characteristics and integral design method of large underwater tunnel structures’and many other major national research projects, systematic studies against the key issues of structure design for large underwater shield tunnels were carried out from the aspects of integrated design method, load calculation, rational structure design parameter and structure analysis method. The main works and research achievements include:(1) The concept of integrated design of underwater shield tunnel is proposed, and then the basic framework of it is established. The goals, the effective factors and the design thoughts are also clarified. The integrated design concept is then proposed, which establishs the evaluation theories and decision methods of integrated design of underwater shield tunnel applying mathematical methods such as Analytical Hierarchy Process(AHP), Fuzzy Comprehensive Evaluation(FCE) and Experts Comprehensive Evaluation(ECE), and then seeks for the optimal design adopting linear programming, nonlinear programming, nonlinear optimization method, Monte Carlo method, and Artificial Neural Network(ANN) method. Finally, an optimization of the design of liner structure of Shiziyang shiled tunnel is adopted using the integrated design method.(2) The producing and effectiveness of the loads acting on underwater shield tunnel are considered from the aspects of the effecting of shield driving to the rockmass and the rockmass-structure interaction. Specifically speaking, they are the effect of slurry during Slurry Balance Shield (SPB) driving, the fluid-mechanical interaction, the interaction of tail void grouting, segment grouting, rockmass and segment structure, which can be summarized as construction effect. Based on this, a modified convergence-confinement method consideration the construction effect of SPB is proposed. Then take Shiziyang shield tunnel of the Guangzhou-Shenzhen-Hongkong High-speed Railway Project as example, a field test of water pressure and earth pressure is carried out in different strata of soft soil, hard rock and uneven hardness strata, which confirms the important effect of construction effect of SPB to underwater shield tunnel with large cross-section from the construction stage to the operation stage, and verifies the adaptability and reliability of the modified convergence-confinement method. Finally, an suggestion of the use of the common load calculation methods for underwater shield tunnel is given.(3) Considering the lining structure properties from the aspects of mechanical behaviors, waterproofing performance, structural reliability, ease of construction as well as project cost and schedule, a new type of double-layer structure composed of non-closed inner lining with segmental lining was proposed to adapt to the riverbed scour and sedimentation and water level change. By comparing in the point of view including manufacture, transportation, installation and behavior of segments, rational structure design parameters about segmental lining dividing, width and thickness of segments were put forward for large underwater shield tunnels. By analyzing the mechanical behavior and waterproofing performance of different joints types and different waterproof types, proposals about joints type and waterproof measures of seams were made for large underwater shield tunnels.(4) The analysis system of segment structure of underwater shield tunnel with large cross-section in the transverse is established considering the structure characteristics and the complicate load conditions, which places the beam-spring model considering the iterative algorithm of joint stiffness first, the beam-spring model considering segment cracking and the shell-spring considering segment breadth second. The system can compressive consider the nonlinear iterative value-taking of joint stiffness, the staggered assembling effect, the influences of segment cracking and breadth. A 3D equivalent axial stiffness model of multiple rings is proposed, which can precisely consider the mechanical characteristics of segment rings and joints. The model makes up for the deficiency of the existed 3D skeleton model, which has large element number and complicate model processing, and provides a practical method for the longitudinal mechanical analysis of segment structure of underwater shield tunnel with large cross-section.