Its steel-concrete towers will make Stonecutters Bridge unique in the world, with the last main span deck to be lifted in the first quarter of 2008, Highways Department Chief Engineer Michael Hui says.

Stonecutters Bridge, straddling Rambler Channel with a main span of 1,018 metres, is a key feature of Route 8 connecting Sha Tin and Tsing Yi. Other features of the 13.6km-long route include three tunnels, with lengths ranging from 1km to 2.1km.

On track: A bird's-eye view of Stonecutters Bridge's East Tower pile cap (left). The bridge will straddle Rambler Channel (centre), with unique bridge towers and a twin-deck girder (right).

World's longest bridge span

Mr Hui tells news.gov.hk that Route 8 is technically comparable to highway projects under the Airport Core Programme, although it is smaller in scale.

"In terms of road length, projects under the Airport Core Programme reached 34km, while Route 8 is only 13.6km. However, Route 8 includes one long-span cable-stayed bridge, Nam Wan Tunnel, Eagle's Nest Tunnel and Sha Tin Heights Tunnel, making it comparable to the Airport Core Programme which comprises the Lantau Link, Cheung Tsing Tunnel and Western Harbour Crossing.

"When compared with cable-stayed bridges - Ting Kau Bridge and Kap Shui Mun Bridge - in Hong Kong, the construction of Stonecutters Bridge will be more challenging as its main span will measure about 1,018 metres, one of the world's longest."

Mr Hui pointed out Stonecutters Bridge's two circular tapered mono-towers will reach a height of almost 300 metres - only 100 metres lower than Two ifc, the tallest building in Hong Kong. Maintenance gantries will be installed on top of the towers to provide inspection access.

Steel-concrete composite structure

Another unique feature of the bridge towers is their composite structure. The top 118-metre steel 'skin' creates a modern look for the bridge, echoing Hong Kong's unique position as one of the most cosmopolitan and vibrant cities in Asia, Mr Hui said.

Straddling Rambler Channel at the entrance to the busy Kwai Chung Container Port, Stonecutters Bridge will have a clearance height and width of 73.5 metres and 900 metres for the passage of super container vessels. It will use 224 stay cables, weighing 7,000 tonnes, the longest one stretching 540 metres. They will radiate like a fan from the tower to the deck.

To ensure safe and smooth marine traffic during the bridge's construction, Mr Hui said a marine traffic liaison group has been set up with representatives from the contractor, container terminal operators and relevant Government departments.

Smooth marine traffic assured

"The contractor has to make reference to vessel schedules, weather and current before deciding when to lift the bridge decks over Rambler Channel. The first deck will be lifted over the sea in mid-2007. The last deck will be erected in the first quarter of 2008, closing the bridge gap. Each deck will weigh about 500 tonnes."

Taking part in the project for years, Mr Hui said the most challenging event he has experienced so far was the international design competition held in 2000, in which a winning design was chosen as the reference scheme and was developed during the detailed design stage.

"It was the first time the Government held such a contest. Therefore we had to sort out everything ourselves, from poster design to inviting adjudicators. While the work pressure was very heavy, it was a challenging task. After the event, we prepared a design competition memorandum which has become a useful reference within the Government.

"The Mainland has also made reference to Hong Kong and held contests to get the best designs for bridge projects, such as the Sutong Bridge in Jiangsu and the Third Nanjing-Changjiang Bridge," he said.

Another big challenge to come

Mr Hui expected another big challenge in 2008, the moment before the last bridge deck is lifted.

"Unlike vehicular flyovers which are rigid in appearance, cable-stayed bridges are more flexible and will be subject to vibration when the wind blows. As a cantilevering construction method will be deployed, the arms will be built out piece by piece from the bridge towers until the halves meet.

"Therefore, the bridge will be the most flexible before the last bridge deck is erected to connect the arms. This will also be the most critical moment for us. We will devise measures to keep the level of vibration to the minimum."

Works on Stonecutters Bridge, at a cost of $2.76 billion, started in April last year and are scheduled to end in mid-2008.