Simplified Procedure to Account for a Weaker Soil Layer in Lateral Load Analysis of Single Piles

This paper presents a procedure to account for the presence of a weaker layer of soil in a beam on nonlinear Winkler foundation analysis of a laterally loaded pile or drilled shaft. Three-dimensional (3D) finite-element (FE) models, considering a single pile embedded in a soil continuum, are used to compute representative p-y curves for various combinations of soil profile and pile diameter. Comparisons between the p-y curves resulting from homogenous and layered soil profiles, in which a weak soil layer is located between two stronger layers, provide the means to identify reductions in the ultimate lateral resistance and initial stiffness of the p-y curves representing the stronger soil owing to the presence of the weak layer. These reductions are characterized in terms of an exponential decay model. Dimensionless parameters are proposed as a means of implementing appropriate reductions for an arbitrary soil profile and pile diameter. Validation of the reduction procedure is conducted through a comparative study, in which the effects of liquefaction-induced lateral spreading on a pile are analyzed using pseudostatic nonlinear Winkler foundation and 3D FE approaches. Use of the reduction procedure is demonstrated with p-y curves defined by existing methods. DOI: 10.1061/(ASCE)GT.1943-5606.0000684. (C) 2012 American Society of Civil Engineers.