Author: Chan, George;Lui, James;Lam, Kelvin;Yin, K K;Law, C W;Lau, Ringo;Chan, Alex;Hasle, Ronan
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Chan, George;Lui, James;Lam, Kelvin;Yin, K K;Law, C W;Lau, Ringo;Chan, Alex;Hasle, Ronan
The Structural Engineer, Volume 82, Issue 20, 2004
In recent years jacked steel H-piles have been introduced into Hong Kong as an alternative to driven piles. In Hong Kong practice, termination of pile driving is often based on dynamic formula and pile tips are normally embedded in a stratum with SPT-N values exceeding 200. On the other hand, installation of jacked piles ceases when the rate of penetration is less than some prescribed termination criterion and jacked piles are normally embedded in layers with SPT-N values of less than 160. As such bearing stratum is less stiff, the load transfer mechanism and capacity of jacked piles could be very different from driven piles and experience from the latter may not be directly applicable. To investigate the behaviour of such piles, a comprehensive study was conducted. In the study, six piles were instrumented with strain gauges and load tested to failure so allowing their load transfer mechanism to be studied. During installation the development of pore pressure around three of the test piles was monitored by electronic piezometers. Different criteria were adopted for determining the termination of jacking. It was found that the test piles passed the same acceptance criteria specified in the building code for driven piles. Shaft friction in the test piles contributed to over 80% of the piles’ ultimate capacity. The pore pressure was found to dissipate quickly after jacked pile installation. P. K. K. Lee, Department of Civil Engineering, The University of Hong Kong L. G. Tham, Department of Civil Engineering, The University of Hong Kong S. T. Chan, Housing Department, the Government of HKSAR F. Yu, Department of Civil Engineering, The University of Hong Kong J. Yang, Department of Civil Engineering, The University of Hong Kong
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. C. K. Chan, Atkins China Ltd Alfred H. K. Tsang, Atkins China Ltd Rex N. Chow, Leighton Contractors (Asia) Ltd Joseph Y. C. Tam, Freyssinet Hong Kong Ltd