Behavior of Pile Foundations in Liquefied and Laterally Spreading Ground

Speaker:
Prof. Scott Brandenberg,
Department of Civil and Environmental Engineering,
UCLAAstract:Structures founded on pile foundations have suffered extensive damage due to earthquake-induced liquefaction and lateral spreading. Damage has been particularly intense when a relatively strong nonliquefied crust layer spreads laterally on top of an underlying liquefiable deposit and exerts large loads on the pile foundations. Lateral spreading hazard poses a large problem for bridges because (1) bridges often cross bodies of water and are founded in a profile consisting of a sloping nonliquefied crust over liquefiable sand, (2) many bridges were constructed before liquefaction and lateral spreading was identified as a hazard to be considered in design, and (3) current design methods have not been sufficiently verified by case histories and model studies. This talk presents a suite of centrifuge studies of pile foundations embedded in a gently sloping profile of nonliquefied clay over liquefiable loose sand over dense sand. The densely instrumented models provide insights into the fundamental mechanisms of load transfer between piles and liquefiable sand, and between pile caps and nonliquefied spreading crusts. The data show how dilatancy (i.e. cyclic mobility) of liquefiable sand affects soil-pile interaction, and how passive loads of laterally spreading crusts are mobilized against pile groups at displacements that are about an order of magnitude larger than observed in tests in nonliquefied soil profiles. Observations from the centrifuge tests led to improved design guidelines for static beam on nonlinear Winkler foundation (BNWF) analyses that are commonly used in design practice. Analyses that utilize the guidelines are shown to reasonably predict pile cap displacements and peak bending moments for cases where the pile groups were laterally stiff to limit damage to the structure. The talk ends with discussion of preliminary results from an ongoing project to develop fragility functions that characterize lateral spreading hazard for approximately 13,000 Caltrans bridges, many of which were not designed to resist lateral spreading loads.

Location: Kaprielian Hall (KAP) - rielian Hall 203

Audiences: Everyone Is Invited

Contact: Evangeline Reyes