ERI: Evolution of Dynamic Behavior of Pile Foundations in Permafrost with Climate Change

该工程研究启动（ERI）奖将支持研究永冻层深层结构基础动力行为演变的研究。桩对地震振动的反应受到温度升高引起的土壤性质变化的影响。阿拉斯加是美国地震最多的地区，也是世界上地震最活跃的地区之一。由于冻土的力学特性依赖于温度，而土壤温度的变化会显著影响冻土地区的地震振动，因此，与融化相关的沉降和频繁的地震活动正在破坏基础设施。因此，对结构稳定性至关重要的土桩基础系统的动力特性不能仅从永久冻土区或非永久冻土区进行测量来预测。本研究将描述和评估持续多年冻土退化对面对地震灾害时桩基动力行为的影响。该项目将为克拉克森大学和阿拉斯加费尔班克斯大学的本科生提供研究经验；他们将协助进行仪器、土壤测试、现场测试和数据处理。此外，还将实施一项针对中学科学课的教育和推广计划，该计划将演示土层中模型桩的动力响应。该ERI研究项目的目标是描述退化永久冻土中桩基的动态行为，这些知识可用于开发受地震和气候变化影响的弹性，可持续的桩基设计，并在降低基础设施维护和运营成本的同时延长使用寿命。为了实现这一目标，将追求两个目标：(1)通过实验室规模的试验，表征冻结和未冻结土层的厚度和分布对土-桩体系动刚度和阻尼的影响；(2)利用原位振动试验研究季节性冻融对阿拉斯加多年冻土区桩动力特性的影响。将回答以下基本问题：(1)在不连续多年冻土区，地面温度分布如何影响土桩系统的动力行为？(2)冻融引起的土层热力特性变化在桩基动力响应中的作用是什么？通过综合实验室和现场试验结果，该研究将改进多年冻土区非线性温克勒地基上的动力梁模型。这项研究将为开发和研究连续和不连续永久冻土带的创新基础解决方案提供基础，从而提高北极地区的社区恢复能力。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This Engineering Research Initiation (ERI) award will support research that investigate the evolution of the dynamic behavior of deep structural foundations in permafrost. Pile response to vibrations from earthquakes is affected by changes in soil properties from increasing temperatures. Alaska has more earthquakes than any other region of the United States and is, in fact, one of the most seismically active areas of the world. Infrastructure is now being damaged by both thaw-related settlements and frequent seismic activity because mechanical properties of permafrost are temperature dependent and soil temperature variation significantly impacts seismic vibrations in the permafrost region. Consequently, dynamic behaviors of a soil-pile foundation system, which are critically important to the stability of a structure, cannot be predicted from measurements taken from permafrost or non-permafrost regions only. This research will characterize and assess the impact of ongoing permafrost degradation on the dynamic behaviors of pile foundations in the face of seismic hazards. The project will provide research experiences for undergraduates from Clarkson University and the University of Alaska Fairbanks; they will assist with instrumentation, soil testing, in situ tests, and data processing. In addition, an educational and outreach program for middle school science classes that demonstrates dynamic response of model piles in layers of soil will be implemented. The goal of this ERI research project is to characterize the dynamic behaviors of pile foundations in degrading permafrost, knowledge that could be used to develop resilient, sustainable designs for piles subject to earthquakes and climate change, and increase service life while reducing maintenance and operation costs of infrastructure. To achieve this goal, two objectives will be pursued: (1) characterization of the effects of thickness and distribution of frozen and unfrozen soil layers on the dynamic stiffness and damping of soil-pile systems using laboratory-scale tests; and (2) investigation of seasonal freeze-thaw effects on the dynamic behavior of piles in Alaska permafrost using in situ vibration testing. The following fundamental questions will be answered: (1) How does the temperature distribution of the ground affect the dynamic behavior of the soil-pile system in discontinuous permafrost regions? and (2) What is the role of changes in thermomechanical properties of the soil layers caused by freeze-thaw in the dynamic response of pile foundations? By integrating experimental results from both laboratory and field tests, the research will improve the model of a dynamic beam on a nonlinear Winkler foundation for permafrost regions. This research will provide the basis for developing and investigating innovative foundation solutions for continuous and discontinuous permafrost zones, thereby increasing community resilience in the Arctic.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.