Instability of a Mono Pile in Flexural and Buckling Modes Due to Lateral Spreading

Instability of pile foundations due to liquefaction of surrounding soil is considered as one of the vital cause of its failure. Many case studies are available, where pile foundations are subjected to severe damage due to liquefaction even though designed with good factor of safety. Assuming incorrect failure mechanism in design is probable reason for these failures. Earlier studies idealize pile as a column, and a buckling mode of failure is postulated as a failure mechanism. Lateral spreading during liquefaction can cause large lateral loads on the pile and induce a different failure mode. This is the focus of the present study. Here pile is idealized as a beam-column and failure analysis is performed against buckling as well as flexural instabilities. By considering flexural as well as buckling instabilities, a simplified approach to quantify the critical axial load on pile is formulated in the present paper. A case study is also presented to demonstrate the calculation of critical axial load. Results from the case study infer that, at certain level of lateral spreading piles fail in yielding rather than buckling, which needs to be given due consideration in the design of pile foundations in liquefiable soils.