Generalised failure envelope for laterally loaded piles: analytical formulation, numerical verification and experimental validation

Abstract

The lateral resistance of pile foundations to combined horizontal and moment loading was examined by means of numerical analyses and experimental tests. Initially, Broms' theory for the lateral capacity of a horizontally loaded pile was revisited and extended to the derivation of closed-form analytical expressions for the failure envelope in moment–horizontal force (M–Q) space for various soil conditions. It is shown that within a limit equilibrium framework the normality of plastic flow is an inherent property of pile response at failure. The developed failure envelope and associated plastic flow rule expressions were numerically verified by way of: (a) a beam-on-Winkler-foundation analysis, in which the lateral soil reaction against a yielding pile was represented by an array of uncoupled non-linear springs, and (b) a continuum mechanics analysis in which both the pile and the soil were discretised with three-dimensional elasto-plastic finite elements. The effect of key model parameters – such as (a) mesh density, (b) soil type and associated strength properties, (c) interface non-linearities and (d) soil constitutive models – on the post-failure response of the pile–soil system were parametrically investigated. Finally, an experimental validation of the problem is also provided through a series of 1g small pile load tests, conducted at the National Technical University, Athens.