Stacked pile solution for axial load–settlement analysis of driven piles in multi-layered soils

Abstract

The load–settlement (Q–s) response of deep foundations is influenced by the soil stiffness. One of the most common methods of installing these foundations is the process of driving, which changes the in situ soil stress and stiffness regime. The stiffness further reduces in a nonlinear manner as the loads and shearing strains increase within the soil. The decay in the stiffness of the soil surrounding an axially loaded pile varies with depth. While a variety of methods is available to predict the nonlinear Q–s response of piles in relatively simpler soil profiles, only select methods can handle the case of multi-layered soils, where the stiffness properties vary between layers. As an alternative, the Randolph analytical pile solution is exploited for (i) developing a new modulus reduction scheme from the back-analysis of load tests on driven piles that also accounts for plasticity of the soil, (ii) devising a methodology for generating modulus reduction curves for individual layers of a multi-layered system, and (iii) formulating a stacked pile model with integration of modulus reduction curves for an improved solution. The back-analysis process accounts for the installation effects on the in situ soil stiffness. A step-wise flowchart and example applications of the methodology are also presented.