China has dusted off a decades old plan to build the world's lengthiest underwater tunnel, right smack in the middle of one of its most earthquake-prone regions.

The Chinese government has announced that it is reconsidering a plan first proposed in the early 1990s to build the world’s longest underwater tunnel in the country’s northeast.

The high speed rail tunnel will traverse the Bohai Bay, connecting Dalian in the south of Liaoning province with the Shandong province city of Yantai.


With a prodigious length of 123 kilometres, the proposed tunnel would be the largest structure of its kind in the world, clocking in at over twice the length of the current record holder, the 54-kilometre Seikan Tunnel which binds the islands of Honshu and Hokkaido in Japan.

According to Wang Mengchu, a tunnel and railway expert from the  Chinese Academy of Engineering, the epic project could reduce travel time across the Bohai Bay to mere 40 minutes. At present, a ferry ride across the bay takes about eight hours, while travelling between the two cities by vehicle means covering 1,400 kilometres of coastal roads.

The project will entail excavation 30 metres beneath the Bohai seabed and will consist of a pair of tunnels containing rail lines which run in opposite directions, separated by a shaft in the middle housing a maintenance track.

The idea of building an underwater tunnel to traverse the Bohai Bay was first floated two decades ago, at which time its cost was estimated to be $10 billion.

Despite the manifest benefits of the project, it was rebuffed by the central government at the time because of its exorbitant expense, as well as its location in one of the country’s most earthquake-prone regions, where its path will traverse  two separate seismic fault lines.

While the operation of underwater tunnels in seismically active areas can still be rendered safe through adequate precautionary measures, geological experts point out that excavation through active fault lines unavoidably entails heightened risk, including the possibility of flooding in the case of displacement.

Despite these concerns, the project has been put before the Chinese legislative assembly every year since 2009, and was incorporated into a regional development plan which received approval from authorities three years ago.

The final fate of the project now lies in the hands of China’s State Council, who lend consideration to its blueprints in April.

According to Wang Mengchu, should the project get the go-ahead, work will commence some time during the 13th Five Year Plan, which runs from 2016 to 2020, with a completion date of 2026 at the very latest.