Fixity of Pile Foundations in Seismically Liquefied Soils for Buckling Calculations–An Eigenvalue Analysis

Abstract eng:
A pile becomes laterally unsupported when the soil liquefies during strong earthquakes. This makes it vulnerable to buckling instability. Buckling is a non-ductile method of failure which results in a rapid collapse and it should be avoided in the design process. This paper presents a simple method, based on an elastic analysis, which may be used to estimate the unsupported buckling length of piles in liquefied soil. The method would be applicable to simple structures such as bridges or jetties, which provide no moment or lateral restraint at the top end of the pile. Most research in the area of pile stability is based on the use of Winkler foundation (p-y method), which models the lateral restraining effect of the soil on the pile as a set of discrete one-dimensional springs distributed along the length of the pile. This paper investigates the stability of pile foundations in liquefied soils via a more accurate three dimensional (continuum) model. The program ABAQUS has been used to build and analyse a finite-element (FE), perfectly elastic, continuum, soil-pile model. Results from the FE, elastic-continuum model, for a pile embedded in [non-liquefied] soil, have been compared with documented equivalent Winkler foundation analytical studies, and experimental results. The FE, elastic-continuum model has then been used to analyse the buckling of pile foundations in liquefied soils for the parameters: depth of liquefaction, stiffness of the liquefied soil, and exposed length of the piles.

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