Interpretation difficulties of pile set-up in sand

© 2015 Taylor and Francis Group, London. The compelling evidence for displacement pile set-up (i.e. capacity gains over time after installation) of shaft friction in sand has led to increasing attempts to incorporate time effects in design practice as well as in probabilistic analyses and numerical modelling. The progression is, however, based on a range of dubious inferences from case history data and trends that display a wide degree of scatter. The existing database of field tests indicates that the majority of the reported cases of set-up were assessed from dynamic load tests and static re-tests and, as a consequence, the interpreted degree of set-up differs from that of a virgin pile. In addition, these cases are usually characterised under the assumption that shaft friction increases vary with the logarithm of time. Recent research also reveals that the jacking procedures commonly employed in pile experiments (to model driven piles) lead to a different ageing behaviour to driven piles. Some of these difficulties are highlighted in this paper with the aim of reflecting current understanding of the phenomenon of pile set-up in sand.