Lin, Wei (CCCC HZM Island and Tunnel Project General Office) | Zhang, Zhigang (CCCC HZM Island and Tunnel Project General Office) | Liu, Xiaodong (CCCC HZM Island and Tunnel Project General Office) | Lin, Ming (CCCC HZM Island and Tunnel Project General Office)
The paper presents how the detailed design of immersed tunnel was conducted to ensure a reliable construction in a design-build contract. Hongkong-Zhuhai-Macau (HZM) immersed tunnel is determined to be a concrete-type tunnel with no external waterproof membrane in preliminary design, crack prevention is highlighted. Further, foundation was re-designed, and negative buoyancy during immersion was specified for safety. The unusual siltation on the gravel bed makes it impossible to place the tunnel element E15. Various monitoring work were carried out to find out the cause, and design report was made to client to solve the problem.
The Hongkong-Zhuhai-Macau (HZM) island and tunnel project is a design-build contract belongs to the 35.6 km Hongkong-Zhuhai-Macau link across sea. The project is for a vehicle highway of 100km/h design speed with double way six lanes. The design is required to meet the standards of both Mainland and Hongkong China whoever is higher. For example, design life is taken as 120 years as per Hongkong requirement rather than 100 years, lane width is taken as 3.75m from roadway standard of Mainland rather than Hongkongߣs. The contract mainly includes a 5.7 km long immersed tunnel and two artificial islands. The islands are for transition between undersea tunnel and bridges. A building is also included in the west artificial island, aiming for a landmark.
The immersed tunnel is made of 33 tunnel elements, each has a typical length of 180m and a mass of around 76,000t. The detailed design and construction starts in parallel from November 2011 and the project has a tight schedule of only 6 years. For, unlike bridge construction that can have as much work face as possible, there is usually only one work face for immersed tunnel, i.e. the tunnel element must be installed one by one. And the installation work exposed to sea loads, time window selection was needed, it was considered extremely challenging to complete the project on time.