A remarkable feat of engineering has been announced as Best Project of the Year by American Engineering Review, ENR, for its mixture of first-of-its-kind technologies and methodologies used in the construction.
Bolted to the seafloor in six individual segments, the Dalian Bay Undersea Tunnel in China spans over 2 miles of water and connects the peninsula-bound city of the same name with the mainland.
The approximately $1 billion project commenced in 2019 and during the four winter seasons of the construction’s duration, temperatures dropped as low as -6° F (-21° C). The conditions required specific pre-tests and important novel adaptations for materials.
Allowing motorists to avoid the lengthy C-shaped stretch of road around the bay, the trip has been shrunk from one hour to just 5 minutes. “The team conducted an investigation on offshore concrete structures ranging from 15 to 86 years naturally exposed in the cold sea areas of China,” Sun Zhu, deputy chief engineer with CCCC First Harbor Engineering Co., the lead contractor on the project, told ENR. “Based on this research, a theoretical model was established to predict the 100-year service life of concrete structures in the marine environment of Dalian’s cold region.”
18 tubes of continuously poured concrete make up the undersea structure, each consisting of 7 segments containing 6 lanes for traffic. The tubes, some of which curve to form the tunnel’s path, were assembled 6 at a time along the edge of the bay in the highest capacity dry dock in all of Asia, which was built just for the project.
The total length of the curve adds up to around 1,050 meters, or around 3,200 feet; making it the tightest curve in an undersea tunnel in China. The segments were bolted onto rocks 32 meters below the sea.
All 18 tubes were laid in just 20 months, and after assembly wrapped up in April 2023, the tunnel was opened in 2024.