Work began yesterday on a 16.2km tunnel between Ningbo, south of Shanghai, and the island of Zhoushan, China Daily reports.
In a world first, China Railway’s 14th Bureau Group started work at both ends at once.
The two sections will meet in the middle, which means that their margin of error is about 2cm.
When a juncture has been effected, the two tunnel boring machines (TBMs) will be dismantled and extracted, the first time such an operation has been attempted.
When complete in 2028, the Jintang Undersea Tunnel will connect Zhoushan to the mainland’s high-speed rail system.
Situated 78m below the East China Sea at its lowest point, the tunnel will have an 11.2km shielded section, allowing trains to pass through it at speeds of up to 250km/h.
China Daily comments that the civil engineering is complicated by the site’s geological conditions, the need to work at pressures, and the unusual length of the excavation, which is nearly 10km longer than the tunnel on the Hong Kong-to-Macao link.
Rarely seen construction complexity
Hu Hao, an engineer working on the scheme, told China Daily there were 28 transitions between soft and hard strata.
“The construction complexity, difficulty and risks involved in this process are rarely seen in the world,” he said.
He added that the TBMs had been modified to improve their ability to dig through both kinds of rock.
One of these TBMs, the Yongzhou, was unveiled in the city of Changsha, in Hunan province, in February.
The machine, built by 14th Bureau and China Railway Construction Heavy Industry Group, measures 135m and weighs 4,350 tonnes. It is equipped with 308 specially designed cutters. It will be responsible for the Ningbo end of the scheme.
Upon completion, the tunnel will be the world’s third-longest undersea railway tunnel, behind Japan’s Seikan Tunnel between Honshu Hokkaido, and the Channel Tunnel linking the UK and France.
However, trains in those tunnels travel at a maximum speed of 160km/h.
Zhoushan and Ningbo are currently connected by a cross-sea bridge and ferries.
When completed, the tunnel will allow commuters to travel from Ningbo to Zhoushan in 30 minutes, compared with 1.5 hours by car over the Ningbo sea bridge.
Trains using the tunnel will be able to travel from Hangzhou, the capital of Zhejiang province, to Zhoushan, in 80 minutes.
Zhoushan is made up of an archipelago of islands in the south of Hangzhou Bay. It has a population of about 1.1 million.
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