Fixed-Head Pile Bending by Kinematic Interaction and Criteria for Its Minimization at Optimal Pile Radius

This study focuses on how to determine an optimal radius minimizing the bending strains of vertical, cylindrical fixed-head piles embedded in a homogeneous elastic stratum in soil-pile-structure systems where the kinematic interaction dominates. In order to determine the appropriate radius, closed form formulae for the bending strains at the head of the piles are derived based on three-dimensional wave propagation theory. A general expression of the closed form formulae can be obtained by normalizing the bending strains with respect to a mean shear strain of the soil medium. The normalized bending strains can be expressed by the radius to height ratio of the piles, the ratio of soil to pile stiffness, and a factor representing the relative amplitude and the phase lag between the loading at the head of the piles and the deformation of the ground. The results of parametric analyses reveal the presence of an optimal radius that locally minimizes the bending strains of the piles. Criteria for determining the optimal radius of soil-pile-structure systems are presented.