Dredgers do the job in record time

PUBLISHED : Monday, 06 July, 1998, 12:00am
UPDATED : Monday, 06 July, 1998, 12:00am

Reclamation of the 1,250-hectare site at Chek Lap Kok was probably the world's largest marine construction project. It required record-breaking amounts of sand, rock and mud using most of the world's dredging fleet.

But the scheme was much more than dredging mud and haphazardly dumping rock and sand in its place.

Instead, a sophisticated monitoring system using global positioning satellite technology was installed to ensure the fill material was put in the correct location.

High-grade rock, for example, was dumped along the length of the proposed southern and northern runways to provide a high-quality foundation.

Poorer quality rock was placed in less critical areas. Marine sand was pumped into areas planned for underground structures including the airfield tunnels and 'dead zones' such as the landscaped sections between the runways and taxiways.

Extensive planning was required to ensure the material was placed where intended, although mistakes did occur. A quantity of rock was put in the area earmarked for the airfield tunnels which caused the contractor considerable difficulties when it began excavating the site.

Construction began in January 1991 when a joint venture between Kumagai Gumi and Maeda of Japan with HAM of Holland won a $614 million advance works contract on the original Chek Lap Kok island.

Work entailed the creation of a 29- hectare platform from which the larger reclamation could be launched. It also included space for site offices for both Airport Authority and contractors' staff.

This began in November 1992 when a $9,041 million contract was awarded to Airport Platform Contractors (APC) by the then-Provisional Airport Authority.

APC was a consortium of six international firms - Costain from Britain, Nishimatsu of Japan, Morrison Knudsen from the United States, China Harbour Engineering, Ballast Nedam from Holland and Jan de Nul of Belgium - formed specially to bid for the reclamation contract.

The last two companies were responsible for all dredging and sand filling, a massive operation that involved 24 dredgers, 75 per cent of the world's fleet, brought in from across the globe.

Their task was to clear 70 million cubic metres of mud from the seabed to provide a firm foundation for the rock and sand fill and reduce settlement to a minimum.

Removal of the mud was done so swiftly that most of the dredgers left nine months ahead of schedule. The trailer dredgers travelled more than 1.6 million kilometres during their time in Hong Kong.

The cracking pace shown by the dredgers was maintained during the reclamation phase when sand and rock was dumped at record speed, so that, by December 1993, Lam Chau, an island 1.6 kilometres west of Chek Lap Kok, was no more and had been incorporated into the ever-expanding reclamation. Sand was imported from marine pits in Hong Kong waters where, during the busiest periods, the volume of material would have filled an Olympic-sized swimming pool every minute.

Enough sand was pumped and dumped into the Chek Lap Kok site to fill 148 Empire State buildings.

The rock came from four islands - Chek Lap Kok, Lam Chau and the Brothers, two islands east of Chek Lap Kok - that had been flattened to just six metres above sea level. In all, 38,000 tonnes of explosive were used during the blasting operation.

A huge fleet of dump trucks, excavators and other equipment was used to haul or dig out the rock blasted from the islands.

Some of the trucks had driven the equivalent of four times around the world by the time they were put up for auction in January 1996. This was seven months after the then-Airport Authority (AA) chairman, Sir Hamish Macleod, ceremoniously blasted the last piece of hillside on June 16, 1995.

At the time he said: 'As one of the largest combined excavation and reclamation projects in history, the contract's completion is a remarkable accomplishment. No such vast enterprise could have been completed on a tight timetable without first-rate co-operation from start to finish.' Overall, the volume of material moved - mud, sand and rock - was 360 million cubic metres. The trucks alone had travelled more than 12 million kilometres, consuming 320 million litres of fuel and wearing out 1,808 tyres.

The airport island, complete with a 13-km seawall, was finished in January 1996, four months ahead of the original 41-month contract.

Right from the start of reclamation, the AA was anxious to start construction of the airport facilities as soon as possible.

Consequently, the airport island was split into eight sectors that were further sub-divided into 23 areas to enable land to be released for follow-on construction works once each portion was completed.

In this way, work on the terminal foundations and other airport facilities was able to begin considerably faster than if the whole island had been completed first.

Work on the terminal foundations began in May 1994, long before reclamation finished 10 months ahead of programme in June 1995.

Foundation construction would have started even earlier but for a bruising 12- week dispute between contractors and the AA which delayed the invitation and award of tenders.