Collaborative Research: Integrated Field and Laboratory Based Assessment of Liquefaction Triggering and Residual Strength of Gravelly Soil

地震中造成破坏的主要原因之一是土壤液化。 液化导致松散的土壤表现得更像重的液体而不是固体，这可能导致建筑物沉降以及山体滑坡和大坝故障。 最近，在2008年中国汶川地震和2014年希腊凯法利尼亚地震序列中观察到了广泛的砾石液化和损坏，证据表明，使用现有液化敏感性方法被认为不可液化的砾石土确实液化了。 这项研究将提供一个基本的理解，以及实际指导评估是否砾石存款将。 这种沉积物被广泛遇到，其潜在的液化通常是我国港口、水坝、堤坝和一般民用基础设施稳定性的关键考虑因素。 将开发的改进程序将提高这些设施的弹性，并将有助于避免不必要的费用时，砾石液化不是一个真正的问题，或更重要的是，强调需要稳定时，砾石液化确实是预期的。 研究小组将建立一个网站，提供砾石液化数据库，并记录所有可用的砾石液化案例。将开发可用于推广目的的液化机制视频，以及关于本研究成果的录制网络研讨会和其他教育资源，重点是砾石土液化评估的推荐程序。对于常规工程项目而言，以可靠、具有成本效益的方式表征砾石土仍然是一项挑战，并且诸如圆锥贯入试验和标准贯入试验等方法被认为是不合适的。 即使对于大型项目，如水坝和能源项目，表征也是昂贵的（如果使用贝克尔测试）和有问题的。尽管如此，由于已知在大量地震中砾石土都会发生液化，因此水坝工程师经常被要求评估砾石液化的可能性，而液化缓解成本通常高达数百万美元。 随着大多数土壤液化工程研究的重点是对砂土和粉质土中液化“触发”可能性的评估，需要新的方法和变革性方法来表征砾石。 在这个合作项目中，有一个协调的计划，结合独特的大规模实验室测试和创新的现场测试在关键的砾石液化现场开发液化触发图表和液化后的剪切强度建议砾石土。 原型300毫米直径的循环简单剪切（CSS）设备已在密歇根大学开发，并将用于评估在实验室中的砾石土的循环（和单调）不排水剪切响应。 最初在中国开发的下一代动态静力触探（DPT）将通过关键仪器进行现代化改造，并将沿着现场剪切波速度（Vs）测量用于现场测试。 现场测试将在美国、中国和希腊进行，利用国际合作伙伴、现场测试公司和组织的资源。 PI将利用最近Cephalonia地震中的砾石液化案例研究，以验证新方法并增加砾石液化的现场性能记录。

One of the leading causes of damage during earthquakes is soil liquefaction. Liquefaction causes loose soil to behave more like a heavy liquid than a solid which can result in settlement of buildings as well as landslides and dam failures. Recently, extensive gravel liquefaction and damage was observed in the 2008 Wenchuan, China, earthquake and the 2014 Cephalonia, Greece, earthquake sequences, and the evidence indicates that gravelly soils that were considered non-liquefiable using existing liquefaction susceptibility methods, did liquefy. This study will provide a fundamental understanding, as well as practical guidance on assessing whether a gravel deposit will liquefy. Such deposits are encountered widely and their potential liquefaction is commonly a critical consideration in the stability of our nation's ports, dams, levees and in general, civil infrastructure. The improved procedures that will be developed will enhance the resiliency of these facilities, and will help in avoiding unnecessary expenses when gravel liquefaction is not really an issue, or more importantly, highlight the need for stabilization when gravel liquefaction is indeed expected. The research team will establish a web-site with a gravel liquefaction database, and document all available case histories of gravel liquefaction. Videos on the mechanism of liquefaction that can be used for outreach purposes will be developed, as well as a recorded webinar and other educational resources on the outcomes of this study with emphasis on the recommended procedures for liquefaction assessment of gravelly soils. Characterization of gravelly soils in a reliable, cost-effective manner for routine engineering projects remains a challenge and methods such as the Cone Penetration Test and Standard Penetration Test are not considered appropriate. Even for large projects, such as dams and energy projects, characterization is expensive (if Becker testing is used) and problematic. Nevertheless, because liquefaction is known to have occurred in gravelly soils in a significant number of earthquakes, dam engineers are frequently called upon to assess the potential for liquefaction in gravels and liquefaction mitigation costs often run into millions of dollars. With the majority of research in soil liquefaction engineering focused on the assessment of the likelihood of "triggering" of liquefaction in sands and silty soils, new approaches, and transformative methods for characterizing gravels are needed. In this collaborative project, there is a coordinated plan that combines unique large scale laboratory testing and innovative field testing at key gravel liquefaction sites to develop liquefaction triggering charts and post-liquefaction shear strength recommendations for gravelly soils. A prototype 300-mm diameter cyclic simple shear (CSS) device has been developed at the University of Michigan and will be used to evaluate the cyclic (and monotonic) undrained shear response of gravelly soils in the laboratory. A next-generation dynamic cone penetration test (DPT) that was originally developed in China will be modernized with key instrumentation and will be used for field testing along with in-situ shear wave velocity (Vs) measurements. Field testing will be conducted in the USA, China, and Greece, leveraging resources from international partners, in-situ testing firms and organizations. The PIs will leverage well-documented case studies of gravel liquefaction in the recent Cephalonia earthquake to validate the new methods and augment the field performance record of gravel liquefaction.