Silt Curtains and Cells
Last year, CCCC companies completed another major component of the program: a $400-million reclamation project that created 209 hectares of land, which will host new shipping and border processing facilities for Zhuhai and Macau in Gongbei Bay. The artificial island is designed to resist a 300-year tidal event. On the other side of the project, China Harbor Engineering Co. Ltd. (CHEC) is at the halfway mark on a $900-million project to build a 150-hectare equivalent just northeast of the Hong Kong International Airport. The project has a 6,140-m-long seawall that includes 134 steel sheet-pile cellular structures, about 34 m long with approximately 30 m diameters. "This is the first time in Hong Kong that reclamation is being done without dredging any marine deposits," says Kim Chuan Lim, CHEC project manager. Environmental concerns dictate that crews cease piling work every May and June, so that the white dolphins can calve, he adds.
CHEC custom-built lifting equipment with a guideframe that can rotate the cellular structures into position before installing them with vibratory hammers, says Lim. "Using cellular structures to form a seawall has been done, but we had never used a scheme with a guideframe that rotates 270°," he says.
Stone columns within the cellular structures and, in front of them, rockfill berms are used for compaction and stabilization. Atop the seawall, geotextiles overlaid with a sand blanket, acting as a curtain to cover the seabed to protect further against sedimentation, says Ian Chung, AECOM's Hong Kong managing transportation director.
CHEC is also in a joint venture with Dragages, a subsidiary of the French contractor Bouygues, and VSL for a $1.7-billion contract to build 9.4 km of viaduct. Its route runs from the border-crossing facility on the island through a tight channel, with the airport directly to the north and a section of virgin land, which cannot be touched, directly to the south. Airport height restrictions affect both construction operations and structures depending on the proximity to the runways. Construction plants used for reclamation were restricted to between 30 and 53 m, says Chung.
The nearly 5,700 segments will be mostly precast; however, because the main channel must be crossed, the balanced cantilevered method is used to place spans that reach 180 m in length, says Lim. Some 20,000 piles are in place, and work has begun on precast caps and piers, he adds.
The 54-month viaduct contract is said to be the territory's largest-ever design-build deal. To the east, China State Construction Engineering has a $1.2-billion contract to build a 1-km-long tunnel and a 1.6-km at-grade section of a link road.
To the west of the tunnel, the main project's bridge structures include both steel girders and cast-in-place concrete spans. Floating concrete mixers and cranes add to the busy water traffic. The 30-m-high piers are supported by steel piles bored 100 m into hard rock from temporary work platforms. Span lengths varied from about 90 m in shallow water to 110 m in deep water, Dong says.
Cable-stayed steel-box-girder structures will be built over three channels to allow marine passage. The pylons for the cable-stayed spans will reach as high as 180 m, Dong adds.
"Everything is big," Dong says.
