Incorporating set-up into reliability-based design of driven piles in clay

A statistical database is developed to describe the increase in pile axial capacity with time, known as set-up, when piles are driven into clay. Based on the collected pile testing data, pile set-up is significant and continues to develop for a long time after pile installation. The statistical database shows that normal distribution can be used to properly describe the probabilistic characteristics of predicted set-up capacity by the Skov and Denver equation. The main objective of this paper is to incorporate the set-up effect into a reliability-based load and resistance factor design (LRFD) of driven piles. The statistical parameters for set-up effect combined with the previously documented statistics of load and resistance can be systematically accounted for in the framework of reliability-based analysis using the first-order reliability method (FORM). Separate resistance factors are obtained to account for different degrees of uncertainties associated with measured short-term capacity and predicted set-up capacity at various reliability levels. The incorporation of set-up effect in LRFD can improve the prediction of design capacity of driven piles. Thus, pile length or numbers of pile could be reduced and economical design of driven piles could be achieved.