Research On Mechanical Behavior Of Double-Layer Lining Strunture For Underwater Shield Tunnel

Large-scale underwater-railway shield tunnel is developing towards the direction of over-length, large cross-section and high hydraulic pressure. Lining consist of segments and formworking concrete is increasingly applied in the shield tunnel in our country at present so as to meet the security requirements of the lining structure durability, high-speed train, anti-impact and inflaming retarding etc. However, there have been deviation and dispute on the understanding of mechanical behavior and the role of the secondary lining in shield tunnel and its calculation methods for a long time.This thesis conducts research on the basis of Shiziyang Tunnel of Guangzhou-Shenzhen-Hongkong Passenger Dedicated Railway, combined with the’Long-term safety and prediction method of underground structures under complex environments’and ’Double-layer lining of shield tunnel structure design theory’projects separately supported by National Basic Research Program of China (973Program) and Fundamental Research Funds for the Central Universities. Theoretical analysis, model test, field monitoring and other research means are mainly adopted to analyze unravel the transverse and longitudinal mechanical characteristics of the double-layer lining in the large-scale underwater shield tunnel, and to explore the interaction mechanism between segments and secondary lining. The main results are as follows:1. Based on analyzing the interaction between double-deck lining of shield tunnel, a new transverse mechanical model of the double-layer lining structure is put forward, and a theoretical-analytical solution about compress stiffness of joint plane and sliding deformation of shear plane are proposed; and then made a comprehensively comparative research on the joint-plane stiffness of double-layer lining, different lining thickness, reasonable construction time of the secondary lining by building nonlinear three-dimensional finite element models. According to segment structural form feature, the high-hydraulic-pressure cutoff value of segmental lining from the respects of joint waterproofing and compressing carrying capacity of the structure are analyzed, and obtained the transverse structura.2. Model test of double-deck lining structure mechanical characteristics under different water and soil pressure fields on the platform of shield tunnel-stratum-hydraulic pressure simulation experimental system which can implement the water and soil pressure separately is conducted so as to realize the mechanical characteristics and change law of segmental lining before and after the operation of secondary lining under design load and overload conditions; discusses the interaction mechanism of double-layer lining; reveals the influence rules of various factors such as grouting default or surrounding rock weakening; ascertains the failure modes of double-deck lining under overload conditions.3. Aiming at transverse characteristics of segmental lining and longitudinal connection characteristics of double-layer lining, three-dimensional shell-spring model is built on the ground of analysis and comparison on longitudinal mechanical model of existing shield tunnels, proved the influence law about effective longitudinal stiffness of double-deck lining caused by different secondary lining thickness and construction length. The longitudinal aseismic mechanical characteristics of shield-tunnel segmental lining and double-deck lining are analyzed by adopting longitudinal response displacement method.4. On the basis of effective axial-stiffness philosophy, model test on longitudinal mechanical characteristics and interaction mechanism for double-deck lining of underwater shield tunnel was conducted, and ascertaining influence law about shield-tunnel segmental lining and double-layer lining caused by such factors such as different formation conditions, local loading and unloading.5. Field-test research relied on double-layer lining of Shiziyang shield tunnel was conducted, ascertaining the impact of synchronized grouting and jack thrust on the segmental lining structure during shield tunneling. The long-term variations of water and soil pressure, hydraulic pressure between double-layer lining are revealed, and mechanical characteristics of segmental lining on the pre and post operation of the secondary lining was contrastive analyzed to realize a comprehensive evaluation of the secondary-lining safety along with long-term monitoring data of the secondary lining.The secondary lining may be adopted as the last line of defense for bearing external loads and waterproofing in engineering circles. This thesis provides theoretical basis and practical methods for designing lining structure of large-scale underwater shield tunnel, and also gives a reference for the reinforcement of existing shield tunnel.