CIVIL & STRUCTURAL ENGINEERING
THE WORLD’S FIRST 15-CELL CATERPILLARSHAPED COFFERDAM DESIGN FOR TUEN MUN - CHEK LAP KOK LINK IN HONG KONG The article presents the technical considerations and challenges in both design and construction associated with the innovative caterpillar scheme and its benefits as compared with the conventional approach using straight diaphragm walls. INTRODUCTION Tuen Mun - Chek Lap Kok Link (TM-CLKL) is a 5 km subsea road link which will provide the most direct route between Hong Kong’s Northwest Territories and Hong Kong Island. It forms part of the Hong Kong - Zhuhai Macau Bridge project which was officially opened in late 2018. The world’s longest sea crossing reduces freight and passenger travel time between the three cities to within an hour and plays an important role in promoting the integration of the Greater Bay area. With an innovative new design and construction approach, the project team successfully overcame the challenges of adverse geology and a tight programme, whilst reducing construction risks and costs. The uniqueness and challenge of the project was influenced by its large scale. Being constructed in newly reclaimed land added another layer of complexity to the engineering challenge. The key scope of this project was to construct the 630 m long and maximum 33 m wide South Cut-and-Cover Tunnel (SCC) and the Southern Landfall Approach Ramp (SAR) at the southern landfall of the TM-CLKL Northern Connection Sub-sea Tunnel Section site which is a newly reclaimed land with more than 20 m thick marine deposit/alluvium. The maximum excavation depth is around 43 m. Instead of the conventional excavation and lateral support scheme with straight diaphragm walls and steel struts, an innovative idea was developed. The idea was to utilise a 500 m long caterpillar-shaped cofferdam with 15 cells, each of which is formed by perimeter diaphragm wall panels installed in an arc shape and laterally supported by reinforced concrete struts at the locations of specially designed ‘Y-panels’ - which presents another world first in terms of slurry trench size and complicated reinforcement. The caterpillar is a sustainable and environmentfriendly solution, achieved through substantially reducing the use of steel struts and ground treatment. The success of the project also relied heavily on the combined use of the computer programmes PLAXIS and SAP2000, which enabled the soil structure interaction analysis of the highly complicated ground structure. 24
THE SINGAPORE ENGINEER September 2020
Figure 1: Tuen Mun - Chek Lap Kok Link project plan.
Figure 2: South Cut-and-Cover Tunnel box structure.
The project demonstrates a high level of innovation, engineering excellence and close collaboration between designers and contractors, which have proven to be key to the success of the overall project, adding tremendous social and economic value to Hong Kong and the Greater Bay Area through improved connectivity.
PROJECT BACKGROUND In August 2013, Dragages-Bouygues Joint Venture (DBJV) was awarded the design and build contract for the TM-CLKL Northern Connection Sub-sea Tunnel Section (Figure 1). The major works under this contract, which is valued at approximately HKD 18.2 billion, included: • Reclamation of approximately 16.5 hectares at Tuen Mun Area 40 as the Northern Landfall of the sub-sea tunnel.
