Pile Design in Seismic Areas: Small or Large Diameter?

Abstract

This work investigates the role of pile diameter in resisting seismic actions, with reference to two example subsoils, namely a dry sand and a fully saturated NC clay. After a ground response analysis in free-field conditions for different values of peak rock acceleration, mobilized soil stiffness and surface acceleration are used as ingredients for assessing the kinematic and inertial moment in a concrete pile. An optimum pile diameter is identified as the one that, while guaranteeing safety, corresponds to the minimum cost. It is also proven that, with a constant value of reinforcement area and length, increasing pile diameter (i.e. increasing safety factor and cost) leads rapidly to failure. Likewise, if pile reinforcement is designed only for inertial action, increasing pile diameter is severely detrimental.