Tension Piles in Sand: A Method Including Degradation of Shaft Friction During Pile Driving

Estimation of the shaft resistance component of the axial capacity of a driven pile into sand involves considerable uncertainty, and most of the current design methods are not consistent with the observed pile behavior during installation and axial loading. In this paper, a method for the estimation of the ultimate uplift shaft resistance of a single pile driven into sand was developed based on a database of 34 pullout pile load tests collected exclusively from the current geotechnical literature. The collected database comprises steel and concrete piles (open- and closedended) driven into loose to very dense sand with varying normalized penetration depth with respect to pile diameter. The developed method accounts for the degradation of shaft friction during pile installation. At any given location, the earth pressure coefficient is assumed to degrade from a maximum value (near the pile tip) to a minimum value as an exponential or as a power function of the length of pile driven past that location. The maximum earth pressure coefficient value has been linked to sand relative density, level of effective vertical stress, and pile diameter. The method is extended for the estimation of the compressive shaft resistance of a driven pile into sand by applying De Nicola and Randolph ( 1) correction for the direction of loading. Comparisons of measured and predicted shaft friction profiles of some field cases showed reasonable agreement and indicated that the method is useful in estimating shaft resistance of driven piles in sand and has sound physical meaning.