Buckling analysis of pile foundation in liquefiable soil deposit with sandwiched non-liquefiable layer

Abstract

Many past earthquakes have shown failure of structures with pile foundations attributed to liquefaction. Various experimental tests have also shown that buckling is one of the credible reasons for the failure of such pile foundations, which gets insignificant lateral support due to seismic liquefaction of surrounding soil. In nature, liquefiable and non-liquefiable soil can occur in alternate layers. However, while estimating the buckling capacity of a pile, there are no specific guidelines available, to the best of the author's knowledge, to reasonably estimate its buckling capacity considering the effect of sandwiched non-liquefiable layer. Some studies recommend to ignore the sandwiched non-liquefiable layer present within a liquefiable deposit and consider it as a full liquefiable layer, which can become too conservative in many situations when both the strength and the depth of non-liquefied sandwiched soil layer are high.In the present work, a rational method of estimating the buckling capacity of pile foundation in liquefiable soil with a sandwiched non-liquefiable layer is proposed through a detailed numerical investigation. The developed numerical model (using Beam on Non-linear Winkler Foundation approach) is validated against the centrifuge results. The model considers the initial imperfection of pile and material nonlinearity of pile and soil. The P-delta effect is also considered in the analysis. Detailed parametric study for major influential parameters on the buckling capacity of the pile foundation has been considered in terms of (a) sandwiched non-liquefiable soil layer's type, thickness, and position, (b) pile length above the ground level, and (c) liquefiable soil's initial relative density and thickness. Based on this study, an effective length factor (β) has been introduced, which can be easily used in standard Euler's buckling equation to find out the buckling capacity of the pile in such layered soil profile. A simple chart has been developed for β, and a step-wise methodology has been proposed with explanatory examples for the estimation of buckling capacity of pile foundation in liquefiable soil having sandwiched non-liquefiable layer, with reference to various influential parameters.