HEAVY construction equipment developed in South Africa has been brought in to help prevent the runway at Chek Lap Kok airport cracking up when it opens in mid-1998. The heart-shaped wheels - popularly known as bonkers - are pulled along at a speed of about 12 km/h to repeatedly pound the ground. The airfield contractor is also using 200-tonne vibrating rollers, equivalent in weight to a Boeing 747 jumbo jet. Provisional Airport Authority head of engineering Dr Graham Plant said the machines were being used to limit ground settlement, which could cost millions of dollars to overcome once the runway was in operation. However, he added: 'I would stake my professional reputation on there being very little settlement.' Concern has been expressed that cracks could develop in the runway if the airport platform was not properly compacted. 'They are totally unsubstantiated,' said Dr Plant. 'I am completely confident with the way we removed the marine mud and prepared the airport platform.' The Provisional Airport Authority has set up a network of monitoring stations around the 1,248-hectare site to measure the natural settlement of rock and sand and the compression of material on the seabed. 'This has helped build up a 3-D picture of the ground and helped predict settlement in future,' said Dr Plant, adding that settlement in the past two years had been well within the authority's limits.