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Hangzhou Bay Bridge
    2008-07-20 14:08:33     CRIENGLISH.com

 The Hangzhou Bay Bridge is the longest cross-sea bridge in the world. Officially opened for traffic on May 1 this year, it connects the municipality of Shanghai and Ningbo in Zhejiang Province in eastern China. Today, we are going to meet some of the constructors and hear about their stories in building the bridge.

The Hangzhou Bay Bridge is a cable-stayed bridge that spans across the Hangzhou Bay off the eastern coast of China. Totaling 36 kilometers, it is the longest trans-oceanic bridge in the world, although it does not have the longest cable-stayed main span.

Construction of the bridge started on June 8, 2003. Various feasibility studies were conducted over a decade before a plan was finally approved in 2003.

With a bay mouth 95 kilometers wide, the Hangzhou Bay is one of the three strongest force tide bays in the world. Complicated weather, hydrology and geological conditions have made construction of a bay bridge nearly impossible. Chief designer of the bridge Wang Rengui says cutting edge technologies were used to overcome the technical difficulties.

"Many innovative technologies were used in the construction of the bridge. When designing, we surveyed and studied all kinds of work ships including piling ships, lifting ships and girder vehicles that are presently in use in the world. We also remodeled and upgraded some of the equipment to meet our needs."

After construction started, builders encountered their first big obstacle, that is the huge reserve of methane gas under the ten-kilometer wide coastline and beach area in the southern bank of the Hangzhou Bay. To avoid methane gas explosion triggered by bored pile construction, thin steel pipes were introduced and were placed in the gas layer. The gas was effectively drained before drilling piles started.

Chief engineer Lv Zhongda says that another breakthrough was the substitution of steel bridge piles for the traditional concrete ones.

"To avoid bridge piers being eroded by the strong under-water tide, we used steel piles instead of the concrete ones that are more vulnerable to erosion. The steel piles can withstand corrosion better and satisfies the load bearing requirements."

In total, 5,600 huge steel piles have been installed with the biggest one being 89 meters long and 1.6 meters in diameter. Several hundred million yuan were spent on quality checks of these steel piles, which have proved to withstand 4,000 tons of force from crash by large vessels.

The bridge itself is 36 kilometers long with six expressway lanes going in two directions. The bridge has two main spans, with a 448-meter northern span, and a 318-meter southern span. A speed limit of 100 kilometers per hour is introduced, and the designed longevity of the bridge is more than 100 years.

Captain of one the piling ships, Li Zhenming, says the GPS system was used for the construction of the bridge.

"Conventional method does not work because construction was conducted at sea. We designed and developed a geographic positioning system especially for operations in the sea. Equipped with the system, the degree of accuracy for piling was within 5 centimeters."

After laying the foundation for piles, how to lay down the bridge became the next challenge for constructors.

The Hangzhou Bay has a 10 meter-wide coast and sand area in its southern bank where crane trucks or ships were not allowed access. To cope with the problem, a huge truck with 640 wheels was built to transport bridge parts. It has effectively kept itself and the load from sinking in the mud. Engineer Liu Naisheng was in charge of the program.

"Each pair of the wheels has the same function. When one wheel is broken, the other would take its place. So the truck is able to work normally. This was to ensure the safe transportation of the bridge parts."

For operations in deep water, a 3,000-ton and a 2,200-ton special floating cranes were also manufactured and put in use to lift the bridge. Chief designer Ni Guoliang explains the function of the floating cranes.

"With these floating cranes, the error can be restricted to 3 centimeters. The eight anchors and anchor lines were the keys in keeping the ship stable."

Ni Guoliang says construction time was very limited to avoid the rainy seasons. Therefore, all the new inventions and other construction efforts had to be successful the very first time.



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