Modified Design Procedures for Bridge Pile Foundations Subjected to Liquefaction-Induced Lateral Spreading-Article

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The study evaluates how superstructure inertia and liquefaction-induced lateral spreading jointly affect bridge pile foundations, with particular attention to earthquake duration. The authors conducted effective-stress nonlinear dynamic analyses of a 2-m-diameter reinforced-concrete pile in a sloping, liquefiable soil profile, using motions representing crustal and subduction earthquakes. They compared the analyses with existing Caltrans/ODOT equivalent static analysis (ESA) procedures and developed revised design guidance.<br /><br />Dynamic analyses showed that pile demands were greater in liquefied sloping ground than in nonliquefied ground, demonstrating that inertia and lateral spreading cannot be assessed independently. Longer-duration motions also increased demands, as the two load effects were more likely to act together.<br /><br />The Caltrans/ODOT approach—combining 100% of lateral spreading with 50% of inertia—slightly underestimated demands even for piles remaining elastic. It also cannot readily assess cases where the applied inertial load exceeds the liquefied soil–pile system’s ultimate resistance. The authors therefore propose an ESA method that estimates displacement using the liquefied-system pushover stiffness and an equal-displacement assumption. It combines 100% of lateral spreading with 60% of inertia for short-duration crustal earthquakes, or 75% for medium- to long-duration subduction earthquakes.<br /><br />The revised method agreed reasonably with dynamic-analysis results for elastic pile response and for some inelastic cases that remained below the ultimate pushover resistance. However, predictions became unreliable when pile-head displacement exceeded the displacement associated with that resistance. For such cases, the authors recommend nonlinear dynamic analysis rather than ESA. The findings are based on a specific modeled pile and soil profile, so application to other designs requires project-specific evaluation.

Keywords

bridge pile foundations

superstructure inertia

liquefaction-induced lateral spreading

earthquake duration

effective-stress nonlinear dynamic analysis

reinforced-concrete pile

sloping liquefiable soil

Caltrans ODOT equivalent static analysis

subduction earthquakes

design guidance