Guoxing Huang

Motion response of immersing tunnel element under random waves

The Hong Kong–Zhuhai–Macau Link project crosses the ocean water of Ling Ding Yang and includes a 10 km long bridge section and a 6 km submerged tube tunnel section. The submerged tube tunnel is to be placed in the base trench at the seabed under 40 m water depth (d). Each tunnel element is 180 m in length, 11.4 m in height and weighs 72,000 tons in air. All tunnel elements are to be constructed on yards onshore, towed to the site location, linked to two stabilising floating pontoons and then ballasted and immersed at the site location with an exposed open wave environment. To ensure that the tunnel element can be immersed and then landed safely and accurately on the base trench during the process, an experimental study with scale model tests was performed to investigate the motion responses of the immersing tunnel element linked to the floating pontoons under random waves. The experimental measurements revealed quantitatively the motion behaviour under different wave climates, immersion depths and negative ballasted buoyancy. The results also demonstrated that the dynamic response of the tunnel element was most severe during the stage of freeboard elimination. The experimental measurements during the freeboard elimination stage were also compared to the numerical simulations for further analysis. Overall, an important conclusion from this study is that the freeboard elimination scenario should be checked against cable breakages and the stability of the tunnel element in the design stage, which has not been highlighted in the literature so far. Also, with the quantitative information, the study illustrates how the weather window for the tunnel element immersion can be determined.

Experimental Study on the Hoist Tensions Between the Immersing Tunnel Element and Floating Pontoons Under Irregular Waves

There are extensive studies on the topic of dynamic interaction between moored floating structures and waves, but the majority of the existing studies concerned the in-place condition of the moored floating system. There are few studies concerned the dynamic response of moored structures during the installation phase, especially for the case of immersion of moored tunnel element. In this study, scale model tests were performed to investigate the motion responses of the immersing tunnel element and hoist tensions between the element and pontoons under random waves. The heave motions of the tunnel were compared under various immersing depths. The comparison showed that the heave of the tunnel element was most severe during the stage of freeboard elimination, which reinforced the conclusion drawn by Song et al. [2014]. The experimental measurements quantitatively clarified the dynamic tensions on the hoist wires between the tunnel element and pontoons under different wave climates, immersion depths and negative buoyancy. In addition, with the quantitative information, the study recommends the operational parameters for the tunnel element immersion.