Evaluation of Pile Foundations Subjected to Liquefaction-Induced Lateral Spreading

There have been many historical cases where pile foundations suffered severe damage from liquefaction during an earthquake. The pile foundation loading and deformation due to liquefaction-induced lateral spreading are two major factors evaluating the behavior of pile foundations for bridges in seismically active areas. This paper presents a preliminary seismic evaluation of pile foundations for a bridge located in the coastal area in California subjected to a lateral spreading hazard. Pile groups consisting of 44 cast-in-steel-shell (CISS) piles with a diameter of 6 feet are proposed to support two bridge towers located on each side of a channel. Liquefaction potential is considered high at the site under the design earthquake event. Liquefiable layers of thicknesses of 28 feet and 26 feet are expected at the east and west sides of the channel, respectively. The potential for lateral spreading under the design earthquake event towards the channel is considered to be high as the stratum of liquefaction appears consistently widespread at both sides of the channel. Pile group deformation and forces resulting from the potential lateral spreading were evaluated for both tower foundations by using an equivalent nonlinear static analysis procedure recommended by the California Department of Transportation (Caltrans). This approach imposes a lateral spreading soil displacement field on the foundation model in which p-y curves are used to consider nonlinear response of soils. Pile foundation deflection, moment and shear corresponding to the imposed lateral soil displacements were then calculated and compared with the performance criteria.