Field study of construction effects in jacked and driven steel H-piles

INTRODUCTION The nuisance of noise and vibration caused by percussive piling of displacement piles has limited the use of driven piles in Hong Kong. As an alternative, pile jacking is quiet and free of strong vibration in use. Recently, pile jacking was introduced to the construction industry in Hong Kong (Chan et al., 2002; Li et al., 2003). Li et al. (2003) and Zhang et al. (2006) described termination criteria for jacked pile construction, and Yang et al. (2006) and Zhang et al. (2006) reported behaviour of several jacked piles. Jacked piles were not previously a recognised type of pile foundation (Buildings Department, 2002), local regulations required that piles be installed by jacking to their approximate founding levels and then driven by hammers to confirm that their final sets were similar to those of equivalent driven piles (Chan et al., 2002). In order to satisfy prescribed final set criteria for driven piles, usually derived from Hiley’s formula, a minimum of 7 m of pile section had to be driven after pile jacking in order to achieve the same nominal pile capacity. In other words, in identical soil conditions the length of a jacked pile is smaller than that of a driven pile to satisfy the same capacity requirement. Several questions on the past practice can be asked by engineers. What are the differences between the stress conditions around a jacked pile and a driven pile? What are the differences between the load-carrying behaviour of jacked and driven piles? Why does final driving on a jacked pile cause a considerable change in the pile behaviour? The objective of this note is, through field tests, to study and compare the construction processes, the stress conditions caused by construction, and the load-transfer behaviour of jacked and driven piles.