Proceedings of the 25th Annual Members' Conference and Eighth International Conference and Exposition, 2000, New York NY, (DFI)
Deep, Large diameter bored piles in Hong Kong, two selected cases
Yvone Franco Crosato
The dense population of Hong Kong requires the construction of tall buildings in reclaimed areas or perched on the slopes of the many hills. The large loads to be supported are carried by deep foundations. Many of those are bored piles, to rock, of diameters up to the 3.0 m of today. Case number one is a site located in reclaimed land in the island of Lantau, at the very exit of the new airport of Chek Lap Kok. The peculiar geology of the site and the large reactions needed to support the 45 story towers require 2500 mm diameter piles to rock. Rock is found 143 meters below ground. The test pile was done to ascertain the technical feasibility of such a diameter pile to the anticipated depth of 155 m below ground level. The presence of discontinuities in soil and rock required excavating the pile with the constant protection of a temporary casing. Additionally we were required to install a permanent casing to rock. The existing technology was therefore stretched to test its limits by constructing a 155.55 m deep bored pile. To our knowledge this is the deepest cased bored pile in the world. Case number two is a re-development perched on the slopes of the hills surrounding Happy Valley in an area previously occupied by two low-rise buildings. To support the anticipated heavy equipment for the constrction of a "U" shaped tangent pile wall it was necessary to engineer and build a temporary platform and access ramp capable of supporting the heavy equipment required to construct the 52 number of 2. M in diameter tangetn piles. Piles are constructed through the existing soil, including old revinforced concrete foundations, deeply into rock to temporarily and construction stages of forming the podium adjacent to the new 61 story building replacing the old low rises. Particular problems of vertical alignment are resolved by using particular technqiues. Large fluid losses and water deepae into the nearby buildings necessitate the adoption of particular intermediate return head to reduce the water head necessary to keep the drill bit clean.
|article #927; publication #54 (AM-2000)|