Predicting pile skin friction in overconsolidated clay

Forty-seven prototype pipe piles were installed and load tested under axial compression to failure at the National Geotechnical Experimentation Site (NGES) located at the University of Massachusetts in Amherst. Predictions of pile capacity were made using several methods of analysis incorporating results from an extensive program of laboratory and in situ testing. Open- and closed-ended piles were installed by driving or jacking in an overconsolidated varved clay deposit. None of the available methods for predicting pile capacity was satisfactory for all the pile conditions investigated. A new effective stress based method was developed to account for the influence of the method of installation (driven vs. jacked) and mode of penetration (plugged vs. unplugged) on pile capacity. The new method makes use of experimentally determined profiles of the coefficient of earth pressure at rest, Ko, and the maximum reconsolidation coefficient of lateral stress, Kcmax, determined with full-displacement penetrometers.