Insight into pile set-up and load carrying capacity of driven piles

Abstract

Pile set-up and pile relaxation refer to the time dependent increase and decrease in the load carrying capacity of driven piles respectively. These two phenomena are governed mainly by the dissipation of excess pore pressure. In the case of pile set-up, the initially induced positive pore pressure within the soil mass becomes almost zero after some time, resulting in an increase in effective stress, whereas in the case of pile relaxation, the reduction of initially induced negative pore pressure causes a decrease in effective stress with time. For the safe and economical design of driven piles, a reliable prediction of the variation in pile capacity is essential. The researchers have tried to understand set-up and relaxation in the past, and attempted to predict the variation in pile capacity. This paper presents an insight into the pile set-up and the time dependent increase in load carrying capacity of driven piles along with some details of pile relaxation through a critical review of experimental and mathematical studies reported until recently. The review shows that the most studies are related to the set-up of driven piles because the driven piles are generally used in loose sandy and soft clayey grounds where set-up phenomenon is often observed. Some empirical relationships have been reported to predict set-up, and demonstrated reasonable success in a number of studies. A number of exploration phase field tests offering potential value in predicting set-up have been identified. A possibility of estimating pile set-up during design stage with the help of relevant subsurface exploration program is also discussed.