Most of design codes assume that pile fails during strong earthquake by lateral spreading. Lateral spreading is based on bending mechanism where the inertia and slope movement causes bending in piles. In essence, piles are considered as beams which are subjected to lateral loads such as slope movement leading to pile failure.
Piles are slender columns with lateral support from foundation soils. When the length of pile increases, the buckling loads decrease with the square of pile length. For buckling failure, soils around the piles lose the confining stress during earthquake and can hardly provide lateral support to piles. As such, the pile serves as an unsupported column with axial instability. It will buckle sideways in the direction of least bending stiffness under axial load.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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