FOUNDATION WORK for the 486m tower that is the last part of the Kowloon Station development in Hong Kong is on schedule for completion in February, despite extremely difficult ground conditions.
The tower will be more than 100 storeys high with a four-level basement. It is being built on a 90m by 76m site surrounded on all sides - by road bridges to the west and south, a cut and cover rail tunnel to the east and Kowloon Station to the north.
Geology comprises reclaimed sand fill to 28m with underlying alluvium up to 12m thick.
Completely decomposed granite lies beneath the alluvium with rock between 53m and 100m below ground level. To make things more complicated, ground investigations revealed a fault zone crossing the site, forming large semi-intact blocks of rock between faults.
Consultant Arup has designed the foundations to act in friction to cope with the difficult ground, using shaft grouting. The system uses tube-a-manchette grout pipes within the cover concrete of the reinforcing of each foundation element: 240 shaft-grouted barrettes, varying in size from 2.8m by 1.5m to 2.8m by 1m are being built. These will sit inside a 76m diameter, 1.5m thick circular shaft-grouted diaphragm wall.
A 26m deep basement will be built with a 6m thick raft that will join the barrettes and diaphragm wall together to resist the high wind loading from the tower.
Foundations are being installed for the Mass Transit Railway Corporation by a joint venture between Bachy Soletanche and Intrafor.