Prediction of High Pile Rebound with Fines Content and Uncorrected Blow Counts from Standard Penetration Test

High-displacement piles have rebounded significantly while undergoing an extremely small permanent set per hammer blow in certain soils. This phenomenon, called high pile rebound (HPR), has occurred in many areas of North America. The Florida Department of Transportation identified HPR at six sites in Florida during the process of driving square, precast, prestressed concrete piles into saturated, fine silty-to-clayey sand and sandy-clay soils. Data on pile driving analyzer deflection versus time were used to develop strong correlations between fines content, uncorrected standard penetration test blow counts (N_SPT), pile displacements, and rebound. The correlations developed in this study allow the geotechnical engineer to predict whether HPR will occur at a proposed site at which high-displacement piles are planned for driving by a single-acting diesel hammer. A design equation relating pile rebound to N_SPT and fines content was developed. The correlations showed that permanent set and rebound were a direct function of N_SPT and fines content of the soil at the pile tip. The design equation provides a methodology that allows prediction of HPR during the design phase.