Evaluating Seismic Displacements and Damage for Pile Foundations undergoing Liquefaction-Induced Lateral Spreading

Abstract

Liquefaction-induced lateral spreading has caused significant damage to pile foundations during past earthquakes. Ground displacements due to lateral spreading can impose large forces on the overlying structure and large bending moments in the laterally displaced piles. Pile foundations, however, can be designed to withstand the displacement and forces induced by lateral spreading. Piles may actually “pin” the upper layer of soil that would normally spread atop the liquefied layer below it into the stronger soils below the liquefiable soil layer. This phenomenon is known as the “pile-pinning” effect. Piles have been designed as “pins” across liquefiable layers in a number of projects, and this design methodology was standardized in the U.S. bridge design guidance document MCEER/ATC-49-1. A number of simplifying assumptions were made in developing this design procedure, and several of these assumptions warrant re-evaluation. In this paper, some of the key assumptions involved in evaluating the pile-pinning effect are critiqued, and a simplified probabilistic design framework is proposed for evaluating the effects of liquefaction-induced lateral spreading on pile foundations of bridge structures. Primary sources of uncertainty are incorporated in the proposed procedure so that it is compatible with the performance-based earthquake engineering framework. The application of the proposed procedure is illustrated through a realistic example.