Chinese engineers had never built an immersed tunnel on the open sea, let alone one that, upon completion, would be the world's longest, at a total length of 6.7 kilometers, and one of the deepest, at almost 45 meters, under China's Pearl River Delta.
The idea of directly linking the economic powerhouses of Hong Kong and Macau—shortening the three-hour drive to about a half hour—had floated around for almost 20 years. But it's no wonder the goal has not been met until now: The approximately 50-km-long new highway system has to squeeze past the Hong Kong airport, including air-space restrictions; traverse the aquatic version of a busy interstate highway; and lie in variable layers of soils, ranging from mucky to clay-like to sandy.
Typhoons and open-sea conditions posed risks. Environmental issues included potential excessive Pearl River silting and disturbing a rare species of white dolphin. And there are three major entities—with three different quality standards—involved: the governments of Hong Kong, Macau and, in between, the Guangdong Province city of Zhuhai.
"It set the tone for a difficult project," says Luo Dong, vice general project manager with China Communications Construction Co. Ltd. (CCCC) With its many subsidiaries and a host of international consultants, CCCC now is building the tunnel as well as two artificial islands on either side, 23 km of bridge structures, two reclamation sites and related link roads.
CCCC has little time to complete the project. The governments want the link operational by 2016, as a precursor to the 20th anniversary of Hong Kong's 1997 handover to China from the U.K.
After years of discussion, the governments of Hong Kong and China launched a five-year feasibility study, in 2004. More than 30 research projects were carried out to support the study, including environmental impact analyses, studies on the project's control points, impacts on the marine environment, and economics and finance, says Tian Feng, deputy general manager with CHELBI Engineering Consultants Inc., a joint venture between Louis Berger International and China Highway Planning and Design Institute Consultants, which is now affiliated with CCCC.
"Hong Kong has British standards, Macau has European standards, and, then, there are Chinese standards," Dong says. Designers opted for the highest standard that applied to each component. For example, European standards for concrete were the highest, Chinese capacity standards called for six lanes, and British standards mandated a 120-year overall design life, Dong says.
The route consists mostly of bridge structures that, at several points, have to allow for passage of thousands of vessels daily, says Dong. There were "long arguments" regarding whether to go with an immersed tunnel or a bored tunnel, he notes, adding, "A tunnel-boring machine would have to go 60 meters deep and would need to be longer [than an immersed option]." The immersed option would be a bit cheaper but less environmentally friendly since, Dong says, "we would have to dredge and build a trench."
Working with international firms—Denmark's COWI, the Netherlands' Tunnel Engineering Consultants, AECOM, Mott MacDonald and Ove Arup, among others—CCCC and its subsidiaries began construction in 2009. The immersed tunnel construction is quite similar to that of the $1.8-billion Busan-Geoje project (ENR 2/2/09, p. 24): Tunnel elements are immersed in a dry dock, towed to the jobsite and then placed atop specially designed gravel beds with tight tolerances. COWI brought its experience on that Korean project to this one, says Tommy Olsen, COWI project manager. COWI worked with HDPI on the preliminary design phase and then with CCCC.