Reliability of Axial Design Methods for Open Steel Piles Driven in Chalk

The prediction of driving resistances and long-term axial capacities for piles driven in chalk suffers from considerable uncertainty that impacts many offshore and onshore projects. This paper assesses the reliability of alternative design methods by checking the accuracy with which conventional and recently proposed approaches can predict a newly collated and independent data set of high-quality static and dynamic pile tests conducted in the UK, France, and Germany, as well as the Axial-Lateral Pile Analysis for Chalk Applying multi-scale field and laboratory testing (ALPACA) joint industry project (JIP) data set from which the recently proposed methods were developed. While the conventional design recommendations by Construction Industry Research and Information Association (CIRIA) systematically underpredict the static shaft capacities of appropriately aged large diameter piles, the Chalk ICP-23 method gave unbiased average predictions for driving resistances and long-term static capacities. It was also found that dynamic analysis of restrike tests on aged piles generates more scattered capacity estimates than static measurements and, on average, marginally higher shaft capacities. The database analysis quantifies the reliability of the alternative design methods and so allows design uncertainties to be reduced considerably.