Plastic Hinge Formation in Pile Foundations due to Liquefaction-Induced Loads

Liquefaction induced soil pressures and lateral spreading demands are often the major cause of pile foundation failures. Review of case studies and data indicate that: (i) liquefaction-induced loads include soil pressures and potentially large displacements due to laterally spreading soil, both of which impose significant deformation demands on below-ground piles, (ii) these large deformation demands may result in plastic hinging of the piles, and (iii) the magnitude, location, and spread of the plastic hinging has not been comprehensively investigated. This numerical study evaluates the inelastic behavior of reinforced concrete pile foundations under liquefiable and lateral spreading soil conditions. The parametric study considers different structural and soil details, as well as different simplified analyses methods commonly used for applying liquefaction-induced demands. The application of liquefaction-induced demands is studied using either (i) applied pressures or (ii) applied lateral spread displacements. Of the available methods for estimating lateral spread displacements, the four parameter empirical model proposed by Bardet et al. (2002), is used and observed to be conservative in comparison with other empirical and analytical models. This investigation reveals that the most pronounced variation in inelastic demands, as characterized by maximum bending moment depth and plastic hinge length, is attributed to the strength and stiffness of the pile as well as the layering condition of the soil. In particular, the existence of a non-liquefiable layer (crust) at the ground surface significantly affects the demands on the pile shaft.