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'Archimedes Bridge' in China?

JIN BO ( China Daily )

People can cross a river via ship, bridge or tun-nel. But how about via a submerged floating tunnel?

More tunnel than bridge, it is a tube-like structure held afloat by tethers, pontoons or columns.

The tube is large enough to carry cars and trains without getting in the way of ships.

It is nicknamed"Archimedes Bridge," since it is based upon the buoyancy concept which was summed up by the well-known ancient Greek mathematician Archimedes.

Zhoushan, a city in East China's Zhejiang Province, is seriously considering building the country's first submerged floating tunnel. The idea has sparked debate among scientists.

Zhoushan, a city comprising 1,390 islands in the East China Sea south of Shanghai, is famous for its abundant ocean resources.

But the city does suffer being separated from the mainland. It lacks efficient transport options to connect it to the city, which prevents it from further developing its economy.

In 1999, Zhoushan launched an ambitious project to link the archipelagoes to other parts of Zhejiang Province.

Once completed, it is expected to turn Zhoushan into a"peninsula."

Officials envision an investment of 8 billion yuan (US$967 million) for six huge bridges and a submerged floating tunnel stretching over the Jintang Strait, if technologically possible and economically affordable.

The strait stretches about 3,000 metres, with an average depth of 50 metres and a maximum depth of more than 100 metres.

The thought of building a submerged floating tunnel has attracted the attention of the Zhejiang provincial government's department of science and technology.

According to Wu Jian, a divisional director at the department, the local government and science authority contacted the Italy-based Archimedes Bridge Co, one of several companies engaged in research and development of a submerged floating tunnel.

Earlier this month, the Chinese Academy of Sciences, the Italian Ministry of Foreign Affairs and the company jointly sponsored a workshop in Beijing, where the feasibility of the Jintang Strait project was discussed.

Said Paolo Bruni, Italian Ambassador to China:"It would boost economic development of the area, preserve the landscape because of the minimal environmental impact and realize for the first time in the world the unique, innovative infrastructure based on the Archimedes Bridge technology."

Besides costing less than a conventional bridge or tunnel, a submerged floating tunnel is also more environmentally friendly.

Unlike a tunnel, which descends to the bottom of a river or sea, this would not require steeply graded approaches and egresses, which cause cars and trucks to consume more fuel.

Supporters say this would reduce the amount of waste products discharged from vehicles.

Despite all the advantages of submerged floating tunnels, many scientists said they do not agree with building such a tunnel in China.

According to Wu Yingxiang, a professor at the Institute of Mechanics of the Chinese Academy of Sciences, the technology has never been put into practical use anywhere in the world.

"It is still quite immature," Wu said.

Although the idea of building a submerged floating tunnel sounds somewhat novel, Wu said, it is not original in scientific circles.

Since the idea was first put forward in the 1960s, curiosity about the technology has spread quickly.

The European Union (EU) has established a study group to evaluate the technology. Many international conferences on the subject have been convened.

Italy has considered an Archimedes bridge to span the strait of Messina.

In 1998, the Norwegian Ministry of Transport proposed the construction of a 1,400-metre-long submerged floating tunnel near Stavanger.

And Switzerland once planned to build a railway in the area of Lake Lugan. A submerged floating tunnel is the best choice to avoid destroying the beautiful lakeside scenery while minimizing the traffic congestion around the lake, officials there said.

Japan also has considered building submerged floating tunnels, including a 30-kilometre-long crossing.

But so far not one of these construction plans has been approved. And the Norwegian and Italian governments have decided not to build submerged floating bridges for the time being, Wu Yingxiang said.

Since this type of structure has never been built, its eventual construction will demand extraordinary vigilance.

Since it will be floating in water, the effect of currents and waves should be taken into account, he said.

As indicated by a similar research project in Norway, currents and waves can move the tunnel about 1 metre in a lateral direction.

"Since there is no technical standards at present, no building company will dare take charge of the construction," Wu Yingxiang said.

Wu said architectural experts at Zhejiang University and the Shanghai-based Tongji University all agreed that construction of a floating tunnel is too early for China.

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