Rail transport A high-speed train beneath the seabed

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China's engineers are on their way to another world record. A few days ago, a tunnel boring machine (TBM) began excavation beneath the seabed to build the longest maritime tunnel for high-speed trains on earth.

Henrik Bork, long-time China correspondent for the Süddeutsche Zeitung (German daily newspaper) and the Frankfurter Rundschau (German daily newspaper), is Managing Director at Asia Waypoint, a consultancy specializing in China, based in Beijing. 

To connect the coastal city of Ningbo with the island of Zhoushan, a 10.05-miles-long tunnel is currently being dug in China up to 255.91 feet deep under the seabed. Excavation began a few days ago. A high-speed train is expected to run there in the future. It is a "technically ambitious project," according to Chinese trade media.

That's even an understatement. On its way to the underground land-sea boundary, the tunnel boring machine "Dinghai" has already successfully tunneled under highway foundations, rivers, and shore dams.

Now it continues below the Jintang sea lane, one of the busiest container ship routes in the East China Sea. Not only must obstacles like oil pipelines be overcome without damage, but also complex geological rock formations in the seabed must be hollowed out.

Two tunnel boring machines are in operation

In addition, the tunnel boring work must be carried out with high precision because two of the 442.91 -feet-long, 9.585-Ibs TBMs are working on the tunnel simultaneously. The Dinghai is traveling from the Zhoushan Island and is expected to meet approximately in the middle with the TBM "Yongzhou," which is burrowing forward from the mainland.

The choice of machines, which are domestically produced, has been very satisfactory, quotes the newspaper China Daily the chief engineer of the project, Zhang Jintao from the "11th Railway Bureau of China." Currently, progress is about 52.49 feet per day.

New prestige project pursues two goals

The Chinese government is pursuing two equally important goals with this latest prestige project. On one hand, the region's infrastructure is being expanded. The island of Zhoushan, with its more than one million inhabitants, is an important transport hub with its sea and river ports, through which China imports oil, minerals, and food and exports containers.

"Zhoushan City" will be connected via this new route for the Chinese high-speed train, the "Gaotie," with the Yangtze Delta and its industrial regions, where almost half of the country's GDP is generated on 21 percent of the land mass of the People's Republic.

On the other hand, beyond the direct benefits of modern infrastructure, Beijing always pursues the goal of active export promotion with such prestige projects. Whereas in the past one had to import German or other foreign tunnel boring machines, Chinese TBM manufacturers like the "China Railway Construction Heavy Industry Corporation" are now already active in the global market. 

Potential customers for TBM machines from other countries can be taken to such construction sites or completed tunnels and be convinced of the technological maturity of Chinese engineering. When a world record is involved, as this time with "the longest undersea tunnel for a high-speed train on earth," it becomes particularly promotional.

Our tunnel boring machines are developed in China, specifically designed for our geological conditions and construction environment. Now that the machine has reached the sea as planned and is gradually completing the tunnel, it will prove that the technology of our manufacturing is not only leading in China but also globally.

Zhang Jintao, Chief Project Engineer

Longest undersea tunnel for high-speed train

When comparing tunnels for slower, conventional trains beneath the seabed, the Seikan Tunnel in Japan and the "Channel Tunnel" between France and England are a bit longer. However, a high-speed train has never been sent on such a long journey below the ocean as now for the route from Ningbo to Zhoushan.

"Our tunnel boring machines are developed in China, specifically designed for our geological conditions and construction environment. Now that the machine has reached the sea as planned and is gradually completing the tunnel, it will prove that the technology of our manufacturing is not only leading in China but also globally," says Zhang Jintao.

Largest network of high-speed rail lines on earth

Within a few years, China has built the largest network of high-speed rail lines on earth, with a total length of 150.929.360 feet. This accounts for 70 percent of the global length of such routes.

Chinese trains not only travel much faster than those in Germany (where, unlike in China, they have not been given their own tracks), but they also arrive much more punctually, partly because they are now maintained with the help of artificial intelligence.

The new undersea tunnel and the completed Gaotie route from Zhoushan to Hangzhou will reduce the travel time from three and a half hours to 77 minutes. The tunnel is expected to be finished by the end of 2026, with trains racing under the sea from 2028.