Search Results (5)

With the rapid development of cross-sea infrastructure, the immersed tube method has been increasingly applied to deep-water immersed-tube tunnel construction. However, when the construction depth reaches the scale of one hundred meters, issues such as high hydrostatic pressure, complex hydrological conditions, and limited construction windows significantly elevate project risks. Against this backdrop, this study systematically reviews relevant domestic and international research findings in the context of 100-m-deep water environments and constructs a comprehensive risk index system covering the construction processes of the WBS breakdown system based on the WBS-RBS decomposition method within the HSE framework. A risk index weighting analysis combines quantitative and qualitative analysis, categorizing the indicators into qualitative and quantitative categories. Quantitative analysis employs threshold determination and the LEC method; qualitative analysis utilizes expert surveys and the G1 method. Ultimately, a model that combines multiple methods for a 100-m-deep water environment, integrating subjective expertise and objective data, is developed. On this basis, multi-level prevention and control measures are proposed for hundred-meter-deep water-immersed tube construction. The results demonstrate that the proposed system can effectively identify key risk sources under deep-water conditions and provide practical countermeasures, offering significant guidance for ensuring construction safety and engineering quality in hundred-meter immersed-tube tunnel projects. Full article

The Chebei integral Immersed Tunnel introduced an innovative full-section interval casting process, where post-casting belts impose restraint effects on the full-section casting segments. To mitigate concrete cracking, this study investigates the influence of the bottom steel plate and steel bars in the post-casting belts on the mechanical behavior of full-section casting segments through comparative analysis of field tests and numerical simulations. Requirements for post-casting belt length are proposed. Key findings include: under post-casting belt restraint, the full-section casting segment’s shrinkage strain reached 348 με, with hydration heat-induced cooling and drying shrinkage contributing 60% and 40%, respectively. A temperature-dependent thermal expansion coefficient model was developed to characterize the nonlinear relationship between concrete strain and hydration heat temperature. Restraint effects diminished with increasing post-casting belt length, and the post-casting belt length should be control. At 1.6 m (Chebei design), restraint-induced tensile stress was 1.4 MPa (restraint coefficient β = 0.12), with the bottom steel plate and steel bars contributing about 70% and 30%, respectively. Relationships between post-casting belt length, stress, and restraint coefficient are established for engineering reference. These research findings have been successfully applied in the Chebei Immersed Tunnel, enabling high-quality prefabrication of full-section interval casting immersed tubes. Full article

Full-section interval casting technology was adopted for the integral immersed tube of the Chebei Immersed Tunnel. Field tests (Chebei Immersed Tunnel) were conducted to establish the time-dependent development of the concrete shrinkage strain of the full-section casting segments. And laboratory experiments were then carried out to investigate the influence of factors such as the reinforcement ratio and stress, expansive agent content and composition, fly ash content, and curing temperature and humidity on the expansive effect of calcium–magnesium composite expansive agents. Field tests revealed that casting segments exhibit initial expansion followed by shrinkage, reaching a final strain of 348 με (microstrain). Laboratory investigations demonstrated that reinforcement (20–30 MPa stress) in post-casting belts effectively restrains segments without compromising the performance of calcium–magnesium composite expansive agents. The optimal 5:3:2 ratio of CaO, MgO 90s, and MgO 200s agents controlled shrinkage strain within 80 με by combining CaO’s rapid early expansion with MgO’s sustained effect. Field validation confirmed the mix’s effectiveness in preventing cracking, with key findings: (1) fly ash content and curing conditions significantly influence expansive behavior, and (2) shrinkage development can be precisely regulated through agent composition adjustments. Full article

This study investigates the impact of fire on the cracking behavior of immersed tunnels. A reduced-scale (1:5) model of an immersed tunnel was constructed to conduct fire tests in both traffic tubes using the HCinc curve as the applied fire. Temperature field changes were carefully monitored during the test by thermocouples and infrared thermography on the outer surface of the tunnel’s ceiling. The continuous temperature field and temperature changes in the concrete cracks were recorded by infrared thermography. By integrating the temperature field distribution in concrete and the behavior of concrete cracking, an analysis of the depth of concrete cracking in the immersed tunnel under fire was conducted. The concrete cracks exceeded 150 mm at 95 min of the fire test. The results indicate that the inner concrete exposed to fire undergoes thermal expansion, leading to tensile cracking of the outer concrete. Additionally, the fire-exposed surface of the tunnel is vulnerable to cracking due to a temperature decrease. Thus, the design of fire resistance of immersed tunnels should take into consideration the potential for concrete cracking caused by thermal strain. Full article

The use of the segmental pipe section immersed tunnel suffers from several problems, such as complex construction, weak foundation, great water depth, great thickness of siltation back on the top of the tube, and difficult settlement control. Based on Winkel’s elastic foundation beam theory, a mechanical calculation model is established according to the case of an inhomogeneous soil layer, and the force and deformation of the structural system of the immersed tube tunnel are calculated based on a bridge in Zhuhai as an example of an immersed tube tunnel. The results show that the derived formula for calculating the allowable differential settlement per unit length of the longitudinally immersed tube is applicable to the sudden change type foundation stiffness deformation model of the natural foundation section of the tube tunnel of the aforementioned bridge in Zhuhai. The relationship between the settlement control index and related influencing factors is analyzed. Hence, a formula for calculating the stratified ground foundation’s integrated bed coefficient is derived, and the equations for tunnel deflection curves and shear forces are solved. A set of calculation methods that are applicable to the foundation settlement control criteria of the segmental immersed tunnel is provided, and the results provide a significant reference for the optimization of the foundation scheme and improvement of the construction process for similar projects. Full article