Pile Foundations Under Inertia and Liquefaction-Induced Lateral Spreading

过去的地震表明，剪切作用引起的横向扩展是桩基倒塌的主要原因。 可液化土壤中的桩基应设计成在振动期间承受横向扩展荷载（运动学）和结构荷载（惯性）。 过去关于反作用引起的横向扩展的后果的研究是相当新的，在某些情况下是相互矛盾的;特别是关于惯性和运动学要求的结合。 这种知识差距既有潜在的不保守和过度保守的后果。 一方面，它在受长期俯冲地震影响的地区，如美国太平洋西北部，日本和南美洲西海岸，带来了相当大的公共安全问题。 另一方面，我们不知道惯性和运动联合收割机在大深度是否以及如何结合。 在某些情况下，后者导致了过于保守和昂贵的地基改善解决方案。 本研究项目将使用五个离心试验的数据，结合先进的数值模拟，在可液化土壤中的桩支撑码头，以深入了解桩在多层土壤剖面与可液化土壤的非弹性行为的建筑物，港口和码头，生命线和桥梁。该项目的广泛影响是多种多样的，包括为从业人员提供设计建议，开发先进的三维数值工具，将提供垂直的步骤，为未来的研究，并在波特兰州立大学发展多样化的岩土工程研究生研究计划。这项研究的总体目标是了解影响如何惯性和摩擦引起的横向扩展（运动学）联合收割机在地震中结合的因素。 在这项研究中的中心假设是，这种组合减少深度和强震持续时间和桩的非弹性增加。 这项研究的目标将通过三个具体目标来实现。 首先，惯性和摩擦引起的运动学的组合将进行评估，相对于深度分析数据，从五个离心试验桩支撑码头进行了Dickenson和同事在加州大学戴维斯分校大型离心机之间的1999年和2000年。 其次，将使用3D数值模型评估强震持续时间对惯性和运动学组合的影响。 3D模型将根据离心试验数据进行验证，并将受到一套频谱兼容的地面运动。 数值分析的结果将被用来检验惯性和运动学的组合随地震持续时间而增加的假设。第三，将使用非弹性桩更新的3D数值模型评估组合惯性和运动学对桩的非弹性需求的影响。 这将允许评估的假设，桩在横向扩展的理由是放大非弹性需求在长期运动。 因此，这项研究整合了基于实验的数据，从物理模型和先进的数值分析。 这项研究的潜在发现将减少在评估桩行为在横向扩展grounds.This奖项反映了NSF的法定使命的不确定性，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.