with closely spaced concrete box-girder decks. From the east approach, a 2.45-km viaduct connects with the mainland. One 5.95-km viaduct links to Yeongjong Island.

During the tender stage, Buckland & Taylor, North Vancouver, British Columbia, provided a conceptual design, which Samsung altered somewhat, says Woon Hong Min, Samsung site representative. For detailed design, the joint venture hired Japan's Chodai Co. Ltd., with locally based Seo Yeong Engineering Co. and Hyundai Engineering and Construction.

Woon Hong Min

A joint venture of British firms Halcrow Group and Arup Group and Korea's Dasan Consultants Ltd. is conducting design checks for the contractor. Yooshin Engineering Corp., supported by Mott MacDonald Group, is the concessionaire's design supervisor. And New York City-based Parsons Brinckerhoff is the lenders' technical adviser.

For the first time in Korea, the detailed design was fast-tracked, saving 19 months on the schedule, says Min. "The basic [fast track] concept came from the U.K.," he says, adding that the system is catching on.

+ click to enlarge

Total expressway, 21 km long, includes 1.48-km cable-stayed span.

Changing Details

Samsung's joint venture altered the pylon shape from a vertically extended rhombus to an inverted Y to ease construction, says Min. It also changed the cable-stayed deck from composite to an orthotropic steel box girder, he adds.

Instead of installing stays strand by strand, as first conceived, the contractor decided to have Japan's Nippon Steel fabricate the entire system. "It's easier to handle. In the factory they fabricate the whole system and we just bring them to the site, and at one time we can install," says Min.

Moreover, the contractor chose to cast span-length viaduct girders and place them with a traveling gantry. The original plan was to place viaducts, as well as the approaches, using the balanced-cantilever erection method using short precast deck elements.

Mike Doran

The joint venture began its 52-month contract in June 2005. At its own risk, the joint venture had earlier started detailed design, site investigations and setup of fabrication facilities at Songdo, says Mike Doran, Amec project director.

Piling work got off to a slow start because the 9.3-m tidal range interfered with the contractor's movement of floating equipment, recalls Min. To get piling back on schedule last year, the contractor increased the equipment from seven to 11 sets and bored 700 piles of up to 3-m diameter down some 60 m to bedrock.

Allan Platt

Erection of the approach spans began last September and crews have been advancing one segment every three days. The approaches are now more than 560 m long. Crews are erecting the generally 145-m-long spans as balanced cantilevers with 3- to 4-m-long match-cast segments. Altogether, 860 of these up to 7.2-m-deep segments are being cast at the Songdo yard.

To speed construction of the viaducts, the 50-m spans are erected with 164 pairs of full-span girders, also cast at Songdo. In the few areas where water is deep enough, the contractor is using a large, floating crane to place girders. But a single overhead gantry system, engineered by Italy's Paolo De Nicola SpA, is installing most of the viaduct deck.

A $10-million multiwheeled transporter, delivered from Italy last year, takes the girders to the gantry, which lifts and places them. The whole assembly is supported by a pair of box girders that advance in turn from pier top to pier top.

Starting last June from deep water on the west side, the contractor has completed some 1.7 km of viaduct. It is now advancing at the rate of one girder every two days.
When the west viaduct is done, crews will move the gantry system to the east side, which will terminate some 700 m short of the shore. Another contractor will take the highway to the viaduct on reclaimed land.

With numerous self-climbing forms shaping the crossing's piers, the main pylons are now about one-third erected and due for completion next March. Their nearly 1,800-tonne deck- level concrete cross-girders were precast and placed with a floating crane this February.

Steeling for the Future

Crews plan to begin erecting the 28,000 tonnes of the deck steelwork in 15-m-long sections, supported by 3,500 tonnes of cables, this October. The contractor will erect two temporary towers at both back spans.

A floating crane will fill the 260-m and 80-m back spans with four box sections up to 112.7 m long, says Alan Platt, Amec deputy project director. The 80-m span will be ballasted with some 600 tonnes of concrete to counterbalance stay forces.

The erection method, devised by Samsung soon after construction started, saves around two months over the method proposed in the original design, says Platt. That plan involved assembling a temporary framework at the pylons and then erecting the deck in short cable-supported sections into the back spans and main spans, simultaneously.

Joint venture member Hanjin Heavy Industries & Construction is fabricating over 70% of the deck steelwork. The rest is being fabricated in Shanghai by Zhenhau Port Machinery Co.

Despite initial piling problems, hyperactive tides and air temperatures that veer from -4¡F to 104¡F, construction is 45% complete and on time, says Amec's Doran. With work now largely out of the water, bridge erection is becoming repetitive, raising confidence in a successful conclusion.

When complete in 2009, the bridge will position the Inchon Economic Free Zone close to the airport, enhancing its attraction to investors. Located just over an hour's drive west from Seoul, the free zone is home to vast new developments. These include the estimated $25- billion New Songdo City, where over 8 million sq m of built space is planned for 600 hectares of reclaimed land facing the Yellow Sea. Planned projects include six towers, now being designed by the New York office of Hellmuth, Obata + Kassabaum Inc. Already, tall buildings are beginning to emerge over the new bridge's landfall.