Bored pile design in stiff clay II: Mechanisms and uncertainty

Paul J. Vardanega*, Michael G. Williamson, Malcolm D. Bolton

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

31 Citations (Scopus)
686 Downloads (Pure)


The soil mechanics related to pile design in clay has been the subject of substantial engineering research. In a companion paper, various codes of practice were reviewed showing the effect on pile capacity of the different global factors of safety that emerge from the various partial factor combinations for the ultimate limit state. Factors of safety are generally specified based on the opinions of experts. In this paper an assessment will be made of various objective procedures that can be used to reduce uncertainty in the design process, especially regarding the adoption of a pile resistance model and the selection of a soil strength profile as part of a ultimate limit state check, and the estimation of pile head settlement in the context of a serviceability limit state check. It is shown that both total stress and effective stress calculation methods are applicable in London Clay. Estimates of settlement using a non-linear soil stress-strain relationship are made and compared with published data. It is shown that the compression of the concrete dominates the settlement of long piles. Given the low settlements observed, recommendations are made for a reduction in standard factors of safety for bored pile design in stiff clays.

Original languageEnglish
Pages (from-to)233-246
Number of pages14
JournalProceedings of the ICE - Geotechnical Engineering
Issue number4
Early online date19 May 2012
Publication statusPublished - 1 Aug 2012


  • Design methods & aids
  • Piles & piling
  • Risk & probability analysis


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