After more than four years of construction, the mainland's first undersea tunnel opened to traffic on April 26 to link Wutong on Xiamen Island and Xiang'an Xibin, the easternmost district of the city.

Before completion of the Xiang'an Undersea Tunnel, travel from the island over bridges was time consuming and inconvenient for both tourists and residents.

The total length of the project reaches 8.69 km while the undersea part is 6.05 km. It covers a sea area of 4.2 km in width.

Long time in coming

Proposals to build such a transport link in Xiamen started as early as 1994, but whether to build a bridge or a tunnel became the main planning hurdle.

Vice-mayor of Xiamen Pan Shijian noted that studies showed "a tunnel has more advantages than a bridge".

"Xiamen is located on the coast where typhoons are frequent," Pan said. "Building a tunnel guarantees the traffic flow and ensures shipping can pass through."

The proposal to dig a tunnel was approved by the government and construction began in 2005.

Self-renovation

Considered the most complex and risky tunnel project undertaken to date on the mainland, half of it was dug through weathered soil, sand and fractured rock.

For more than four years, the tunnel's builders were required to come up with innovations that solved the technical difficulties. Their work is seen as an achievement in the history of tunnels worldwide.

Among the problems faced were:

Undersea fractures made construction even more risky, requiring development of a special grouting technology.

There were four areas of such fractures during the construction.

A permeable sand bed required building of temporary walls and 200 wells to control the water level.

Extremely weathered soil layers. To solve the problem, builders divided the tunnel into smaller areas that were dug in sequence.

The width of the cross section was 17.5 m.

The project is constructed under 70 m of the sea. There were no deaths among workers during construction.

Significance

The new undersea tunnel is also expected to aid in attracting investors to Xiang'an. During construction, many enterprises from Taiwan and Hong Kong came to explore business opportunities in the city.

The tourism sector in Xiang'an is also expected to benefit.

(China Daily 05/27/2010 page16)