DEVELOPMENT OF A DESIGN GUIDELINE FOR BRIDGE PILE FOUNDATIONS SUBJECTED TO LIQUEFACTION-INDUCED LATERAL SPREADING-PDF

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This report develops an equivalent static analysis (ESA) guideline for bridge pile foundations subjected to liquefaction-induced lateral spreading, with particular attention to long-duration earthquakes and inelastic pile behavior.<br /><br />Researchers performed effective-stress nonlinear dynamic analyses (NDA) of a 2 m reinforced-concrete pile in liquefiable sloped ground, using ground motions representing crustal and Cascadia subduction earthquakes. Analyses compared liquefied, sloping-ground conditions with nonliquefied, level-ground conditions and assessed the Caltrans/ODOT method, which combines 100% of kinematic loading with 50% of inertial loading.<br /><br />The NDA results showed that pile demands were higher when liquefaction-induced spreading and superstructure inertia acted together; considering the effects separately could therefore underestimate demands. The existing ESA method slightly underestimated demands, particularly for long-duration subduction motions, and could not address some inelastic cases.<br /><br />The report proposes retaining 100% of the kinematic demand while using an inertia multiplier of 60% for short-duration crustal earthquakes and 75% for medium- to long-duration subduction earthquakes. This revised method, including an equal-displacement approach to estimate inelastic response, agreed reasonably well with NDA results when pile displacement remained below the displacement associated with the ultimate force on the liquefied-condition pushover curve.<br /><br />ESA predictions became unreliable when displacement exceeded that threshold, as pile response could become unstable. Nonlinear dynamic analysis is recommended for those cases. The findings are based on a limited motion suite and one pile-and-soil configuration; further analyses are needed to validate the approach across a broader range of ground motions, pile geometries, and soil conditions.

Keywords

equivalent static analysis

bridge pile foundations

liquefaction-induced lateral spreading

nonlinear dynamic analysis

reinforced-concrete pile

superstructure inertia

kinematic loading

subduction earthquakes

inelastic pile behavior

equal-displacement approach