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

地震引起的液化的后果并不是微不足道的;例如，新西兰最近的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，从阿拉斯加到加州，向东到新马德里地震带和沿海的南卡罗来纳州，向北到圣劳伦斯航道，都容易受到地震的影响。 新西兰和其他国家的地震使人们意识到，我们对自然土壤沉积物周期性反应的理解存在局限性。 这些局限性是由于继续使用传统的简化岩土分析的做法而产生的，这种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是沿着这两条不同的路线发展起来的。 然而，许多天然土壤沉积物并不适合这些简单的类别，过渡性粉质土，本研究的主题，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，回答有关过渡性粉质土的循环响应的相关问题，这将提高我们对大地震期间大变形和生命财产损失的潜力的理解。 这项研究的结果将在全国和地球仪上得到广泛应用。 此外，这项研究还将有一个平行的目标，即激励下一代STEM领导者。 与位于俄勒冈州纽波特的哈特菲尔德海洋科学中心（HMSC）合作，将使我们的外联工作每年能够接触到15万名游客和4万名K-12学生和教师，通过：（1）液化和现场循环试验的大型移动的振动筛卡车的公开演示，（2）视频演示、数据汇编，和采访的研究人员到一个永久的互动展览，和（3）开发的教学模块，为HMSC的工作人员，以帮助他们建立的推广工作扩大教学，包括沿海灾害，如卡斯卡迪亚俯冲带和相关的海啸。 这些演示将被用来形成永久性展览和教学模块，这将大大扩展这项推广工作。这项研究将提高我们对淤泥土的原位和实验室循环响应的理解，包括非线性，刚度退化，触发不稳定的超孔隙压力，以及相应的后震动后果。 具体而言，本研究将：（1）缩小区分“砂样”和“粘土样”对循环剪切应力/应变的响应的阈值细粒含量和塑性，并确定临界阈值状态;（2）比较过渡性土壤的原位、单轴和双轴循环响应，以了解强地面运动方向性的变化如何影响孔隙压力和体积应变的产生;（3）确定土壤组构、应力历史和饱和度对过渡性土壤循环和循环后响应的影响;（4）将本工作的区域研究结果与以前对过渡性土壤的研究结果联系起来;以及（5）通过一个长期的、协调的推广计划，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者。 这项工作集中在实验，目标小到大的剪切应变，使用的技术，范围从现场循环加载从大型移动的振动筛和爆炸液化，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，关键是提高理解的原位和元素水平的循环响应被桥接。

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.