China revives plans to build world’s longest underwater tunnel in earthquake-prone area

In its latest display of engineering ambition, China may build a 123 km underwater high-speed rail tunnel that is more than twice as long as any in existence today, though the project is loaded with financial and seismic risks.

The proposed tunnel – first mooted 20 years ago – will connect the cities of Dalian and Yantai, which sit either side of a narrow point of Bohai Bay. Currently, traveling from one to another requires a road journey of 1,400 km across the coast, or an 8-hour ferry.

"Using the tunnel, it will take only 40 minutes to travel from Dalian to Yantai," Wang Mengshu, a tunnel and railway expert at the Chinese Academy of Engineering, who is working on the project told China Daily newspaper.

“The project is expected to be started within the period of the 13th five-year plan - 2016 to 2020."

It is set to be completed by 2026 at the latest, he said.

The passageway will consist of two tunnels with rail lines running in each direction, with carriages on which cars and cargo will be loaded. A maintenance track will be placed in a shaft between them, with all three passageways located in the rock about 30 meters below the seabed.

The final decision now rests with the State Council, which will examine the blueprints in April, though the project was included in a regional plan rubberstamped three years ago.

Still, the fate of the tunnel is not set in concrete.

The idea was first proposed in 1994, with a stated cost of $10 billion, and its current incarnation has been submitted to the Chinese parliament every year since 2009, without receiving the go-ahead.

Objections are twofold.

The prohibitive cost of the tunnel, currently estimated at 220 billion yuan, or $36 billion, which is almost certain to rise – the Channel Tunnel, the third longest in the world, came in at almost twice its original budget.

But Wang believes that the tunnel will pay for itself in just twelve years, through increased industrial efficiencies, additional tourism flows, and the relief it will provide to existing communication networks.

The second issue is that the projected tunnel will pass through two separate fault lines. A 7.5 magnitude earthquake in the region in 1976 killed several hundred thousand people.

"In general, though, one can say tunnels are not unsafe in earthquake areas, all depending on the geology, tunnel depth and other local conditions," Matthias Loftsson, director of geology for Iceland's Mannvit engineering company told China Daily.

"However, excavation of a tunnel through active faults, where displacement can occur with a potential danger of flooding, would be of great concern and needs special attention.”

If the project does go ahead, it will comfortably beat not only the 50 km long Channel Tunnel, but the current record-holder, the 54-km Seikan Tunnel that links the Japanese islands of Honshu and Hokkaido to the title of the world’s longest underground tunnel.