Neutral Plane Solution for Liquefaction-Induced Down-Drag on Vertical Piles

Abstract

Down-drag loads on pile foundations can be an important design consideration when earthquake-induced liquefaction is expected to cause ground settlements. A modified neutral plane solution for liquefaction-induced down-drag on vertical piles is described that accounts for the variation in excess pore pressures and ground settlements over time as a liquefied layer reconsolidates, the dependence of sand compressibility on excess pore pressure ratio, and the dependence of shaft skin friction on the excess pore pressure ratio. A worked example illustrates the role of various parameters on peak pile loads and settlements. The modified solution predicts substantially smaller pile settlements than obtained from a traditional neutral plane solution for end-of-consolidation conditions. Recommendations for design practice are presented.