Pile Foundations Under Inertia and Liquefaction-Induced Lateral Spreading

Portland State University, Portland OR

Investigators

Abstract

Past earthquakes indicate that liquefaction-induced lateral spreading is a major cause of collapse of pile foundations. Pile foundations in liquefiable soils should be designed to sustain both lateral spreading loads (kinematics) and structure loads during shaking (inertia). The past research on the consequences of liquefaction-induced lateral spreading are fairly new and in some cases contradict each other; specifically, on the combination of inertia and kinematic demands. This knowledge gap has both potentially un-conservative and over-conservative consequences. On one hand, it poses considerable public safety concerns in regions affected by long-durations subduction earthquakes, such as the U.S. Pacific Northwest, Japan, and the western coast of South America. On the other hand, we don't know if, and how, inertia and kinematics combine at large depths. The latter has resulted, in some cases, in excessively conservative, and costly, ground improvement solutions. This research project will use data from five centrifuge tests on pile-supported wharves in liquefiable soils combined with advanced numerical modeling to contribute in-depth understanding of the inelastic behavior of piles in multi-layer soil profiles with liquefiable soils for buildings, ports and wharfs, lifelines and bridges. The broader impacts of this project are diverse and include providing design recommendations for practitioners, developing advanced 3D numerical tools that will provide vertical steps for future research, and growing a diverse geotechnical graduate research program at Portland State University. The overall objective of this research is to understand the factors that affect how inertia and liquefaction-induced lateral spreading (kinematics) combine during earthquakes. The central hypothesis in this research is that this combination reduces with depth and increases with strong-motion duration and pile inelasticity. The objectives of this research will be pursued through three specific aims. First, the combination of inertia and liquefaction-induced kinematics will be evaluated with respect to depth by analyzing data from five centrifuge tests on pile-supported wharves that were conducted by Dickenson and coworkers at UC Davis large centrifuge between 1999 and 2000. Second, the effects of strong-motion duration on the combination of inertia and kinematics will be evaluated using 3D numerical models. The 3D models will be validated against centrifuge tests data and will be subjected to a suite of spectrally-compatible ground motions. The results of numerical analysis will be used to test the hypothesis that the combination of inertia and kinematics increases with earthquake duration. Third, the effects of combined inertia and kinematics on inelastic demands of piles will be evaluated using 3D numerical models updated with inelastic piles. This will allow assessing the hypothesis that inelastic demands of piles in laterally spreading grounds are amplified during long-duration motions. This research thereby integrates experiment-based data from physical models and advanced numerical analysis. The potential findings of this research will reduce uncertainties in evaluating pile behavior in laterally spreading grounds. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.