Prebored friction mini-pile foundation for light rail grade separation

摘要

Construction access constraints and an undulating rock profile, up to 90m deep in places, dictated use of an innovative foundation solution on the Kowloon Canton Railway Corporation's Light Rail Grade Separation project in Hong Kong. Pre-bored friction mini-piles, were adopted to overcome geological and other constraints, which included low headroom due to overhead cables and strict vibration limits imposed by an adjacent Viaduct Structure supporting Light Rail tracks. Bored piles and socketted H-piles on rock are not commonly adopted for depths greater than 60m due to the construction difficulties. Moreover, the expected high vibration levels generated during pile driving ruled out use of percussion piling. Hence Atkins China Ltd working together with Leighton Contractors (Asia) Ltd (LCAL) and Freyssinet Hong Kong Ltd, developed the use of 450mm diameter pre-bored friction piles as a cost effective and practical alternative. In this paper, the design, quality control on site and the results from proof load testing of the trial piles will be discussed. The friction mini-pile foundation system adopted was designed to comply with requirements stipulated in Hong Kong Building's Ordinance. LCAL commenced foundation works in April 2003 and completed their works in November 2003.