Combined Pile Foundation System for a Residential Complex

Abstract

For a high-rise residential complex in an urban area of Hong Kong, a large diameter bored pile foundation with steel stanchions was proposed to facilitate a top-down construction of a 3-level basement while allowing a concurrent construction of the superstructure. The final column load in some locations was too large to be supported by a single mega sized bored pile and hence supplementary bored piles were required to be built adjacent to the central bored pile with a connection via the pile cap to share the final structural loads. However, the capacities of these supplementary piles would not be fully utilized since the central bored pile directly supporting the column had been loaded prior to the connection via the pile cap. In lieu of the above, a collaborative effort among the designers and the Contractor was made to devise a combined foundation system using pre-bored H-piles to replace the supplementary bored piles. The innovative aspect was to apply pre-loading at the pile heads of the pre-bored H-piles using synchronized jacks upon reaching the pile head level with consideration of compatibility of pile head displacement in order to achieve full utilization of the capacities of both the central bored pile and the supplementary pre-bored H-piles under the permanent loading condition. This combined foundation system with pre-loading at the head of pre-bored H-pile resulted in substantial reduction in volume of pile excavation, lower construction risk, higher degree of flexibility in the construction programme, as well as lower construction cost.