Collaborative Research: Bridging the In-situ and Elemental Cyclic Response of Transitional Soils

地震引起的液化的后果不是微不足道的；例如，最近新西兰坎特伯雷地震序列造成的土壤液化造成了150亿美元的损失。美国的大部分地区，从阿拉斯加到加利福尼亚，东到新马德里地震带，南卡罗来纳沿海，北到圣劳伦斯海道，都容易受到地震的影响。诸如在新西兰和其他地方发生的地震使人们意识到我们对自然土壤沉积物循环反应的理解存在局限性。这些限制是由于继续使用简化岩土分析的传统做法，考虑了两种主要的土壤类型：排水砂和不排水粘土。几乎所有岩土工程系统的设计方法都沿着这两条截然不同的路线发展。然而，许多天然土壤沉积物不属于这些简单的类别；过渡性粉质土壤，本研究的主题，就是一个例子。本研究旨在通过系统和协调的现场和实验室研究来回答有关过渡性粉质土壤循环反应的相关问题，这将提高我们对大地震期间大变形和生命财产损失的可能性的理解。本研究成果将在全国乃至全球范围内具有广泛的应用价值。此外，这项研究将有一个激励下一代STEM领导者的平行目标。与俄勒冈州纽波特的哈特菲尔德海洋科学中心（HMSC）合作，我们将通过以下方式，每年向15万名游客和4万名K-12学生和教师提供服务：(1)用大型移动振动车进行液化和现场循环试验的公开演示；(2)将视频演示、数据和对研究人员的采访汇编成永久性互动展览；(3)为HMSC工作人员开发教学模块，以帮助他们扩大教学范围，包括卡斯卡迪亚俯冲带和相关海啸等沿海灾害。这些示范将形成永久性的展览和教学模块，这将大大扩展这种推广工作。本研究将提高我们对粉土的原位和室内循环响应的理解，包括非线性、刚度退化、失稳超孔隙压力的触发以及相应的震后后果。具体而言，本研究将：(1)缩小循环剪切应力/应变下“类砂”和“类粘土”响应的阈值细粒含量和塑性，确定临界阈值状态；(2)对比过渡土的原位、单轴和双轴循环响应，了解强地震动方向性变化对孔隙压力和体积应变产生的影响；(3)确定土壤结构、应力历史和饱和度对过渡土循环和后循环响应的影响；(4)将本工作的区域发现与以前过渡性土壤的工作联系起来；(5)通过长期协调的外展项目，激励未来的地震学家、地质学家、地震工程师以及自然灾害和恢复规划人员。这项工作集中在针对从小到大的剪切应变的实验上，使用的技术范围从大型移动振动筛和爆炸液化的原位循环加载，到专门和协调的实验室测试，允许开发一个前所未有的数据集，这对于提高对原位和元素水平循环响应的理解至关重要。

The consequences of earthquake-induced liquefaction are not trivial; for example, $15B of damage was attributed to soil liquefaction resulting from the recent Canterbury Earthquake Sequence in New Zealand. Large portions of the United States, from Alaska to California and eastward to the New Madrid Seismic Zone and coastal South Carolina and north to the St. Lawrence Seaway, are prone to the impacts from earthquakes. Earthquakes such as those in New Zealand and others have raised awareness about limitations in our understanding of the cyclic response of natural soil deposits. These limitations have arisen through continued use of the traditional practice of simplifying geotechnical analyses by considering two main soil types: drained sands and undrained clays. Design methodologies for nearly all geotechnical systems have developed along these two distinct lines. However, many natural soil deposits do not fit into these simple categories; transitional silty soils, the subject of this research, are an example. This study aims to answer pertinent questions concerning the cyclic response of transitional silty soils through systematic and coordinated field and laboratory studies that will improve our understanding of the potential for large deformations and loss of life and property during large earthquakes. The findings of this research will have broad application across the nation and globe. Furthermore, this research will have a parallel objective of inspiring the next generation of STEM leaders. Collaboration with the Hatfield Marine Science Center (HMSC) in Newport, Oregon will allow our outreach efforts to reach 150,000 visitors and 40,000 K-12 students and teachers per year, through: (1) public demonstrations of liquefaction and in-situ cyclic tests with a large mobile shaker truck, (2) a compilation of video demonstrations, data, and interviews with the researchers into a permanent interactive exhibit, and (3) development of instructional modules for HMSC staff to help their established outreach effort expand instruction to include coastal hazards such as the Cascadia Subduction Zone and associated tsunami. The demonstrations will be leveraged to form permanent exhibits and instructional modules, which will greatly extend this outreach effort.This research will improve our understanding of the in-situ and laboratory cyclic response of silt soils including nonlinearity, degradation of stiffness, triggering of destabilizing excess pore pressures, and the corresponding post-shaking consequences. Specifically, this study will: (1) narrow the threshold fines content and plasticity separating "sand-like" and "clay-like" responses to cyclic shear stresses/strains and identify critical threshold states; (2) compare the in-situ, uniaxial and biaxial cyclic response of transitional soils to understand how changes in strong ground motion directionality impacts generation of pore pressure and volumetric strain; (3) determine the effect of soil fabric, stress history, and degree of saturation on the cyclic and post-cyclic response of transitional soils; (4) link the regional findings from this work to previous efforts on transitional soils; and (5) inspire future seismologists, geologists, earthquake engineers, and natural hazard and resilience planners through a long-lived, coordinated outreach program. This work concentrates on experiments that target small-to-large shear strains, using techniques that range from in-situ cyclic loading from large mobile shakers and blast liquefaction, to specialized and coordinated laboratory tests, allowing the development of an unprecedented dataset critical for improving the understanding of the in-situ and elemental level cyclic response to be bridged.