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

地震造成破坏的主要原因之一是土壤液化。液化使松散的土壤表现得更像一种重液体而不是固体，这可能导致建筑物的沉降，以及山体滑坡和大坝的破坏。最近，在2008年中国汶川地震和2014年希腊塞弗罗尼亚地震序列中观察到广泛的砾石液化和破坏，证据表明，用现有的液化敏感性方法认为不可液化的砾石土壤确实液化了。该研究将为评估砾石矿床是否液化提供基础认识和实践指导。这种沉积物分布广泛，其潜在的液化通常是我国港口、水坝、防洪堤以及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增强这些设施的弹性，并有助于在砾石液化不是问题时避免不必要的费用，或者更重要的是，当砾石液化确实预期时，强调稳定的必要性。研究小组将建立一个网站，其中包含砂砾液化数据库，并记录所有可用的砂砾液化案例历史。将制作可用于外联目的的关于液化机制的视频，以及关于这项研究成果的网络研讨会和其他教育资源，重点是砾石土壤液化评估的建议程序。在常规工程项目中，以可靠、经济的方式对砾石土进行表征仍然是一个挑战，锥贯入试验和标准贯入试验等方法被认为是不合适的。即使是大型项目，如水坝和能源项目，描述也是昂贵的（如果使用贝克测试）和有问题的。然而，由于已知在大量地震中砂砾质土壤中发生了液化，水坝工程师经常被要求评估砂砾的液化潜力，而减轻液化的费用往往高达数百万美元。由于土壤液化工程的大部分研究都集中在评估砂土和粉质土“触发”液化的可能性上，因此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，结合了独特的大型实验室测试和关键砾石液化地点的创新现场测试，以开发液化触发图表和液化后砾石土的抗剪强度建议。密歇根大学已经开发了一个直径300毫米的循环单剪（CSS）装置的原型，并将在实验室中用于评估砾石土的循环（和单调）不排水剪切响应。最初在中国开发的下一代动态锥突测试（DPT）将配备现代化的关键仪器，并将与原位横波速度(v)测量一起用于现场测试。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地震中有充分记录的砾石液化案例研究来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.