Construction of simplified design p-y curves for liquefied soils

In practice, laterally loaded piles are most often analysed using a ‘beam-on-non-linear-Winkler-foundation’ approach, whereby the soil–structure interaction is modelled by means of p–y curves. Although well-calibrated p–y curves exist for non-liquefied soils (e.g. soft clay and sand), the profession still lacks reliable p–y curves for liquefied soils. In fact, the latter should be consistent with the observed strain-stiffening behaviour exhibited by liquefied samples in both element and physical model tests. It is recognised that this behaviour is induced by the tendency of the liquefied soil to dilate upon undrained shearing, which ultimately results in a gradual decrease in excess pore pressure, and consequent increase in stiffness and strength. The aim of this paper is twofold. First, it proposes an easy-to-use empirical model for constructing stress–strain relationships for liquefied soils. This only requires three soil parameters which can conveniently be determined by means of laboratory tests. Second, it introduces a method for the construction of p–y curves for liquefiable soils from the proposed stress–strain model, based on the scaling of stress and strain into compatible soil reaction p and pile deflection y, respectively. The scaling factors for stress and strain are computed following an energy-based approach that is analogous to the upper-bound method used in classical plasticity theory. To validate the proposed p–y curves, results from a series of centrifuge tests are employed to back-calculate p–y curves for liquefied soils. The latter are compared with those obtained from the proposed method and the conventional p-multiplier approach.