Evaluating Liquefaction Potential of Challenging Soil Sites: Linking Geomorphological Controls and Novel Approaches for Site Characterization

这个项目的重点是改进工程模型，以预测地震引起的液化的严重程度，这些地点位于“具有挑战性的土壤场地”。液化是指松散、饱和的沙质土壤在地震震动时失去强度，导致附近基础设施严重受损的现象。新西兰克赖斯特彻奇最近发生地震后进行的现场调查突出了当前工程液化严重程度模型的局限性，该模型适用于粘土层夹杂在可液化砂层中的剖面(即“具有挑战性的土壤场地”)；类似的地质剖面在美国和世界各地都很常见。然而，模型缺陷的根本原因尚不清楚。不能准确预测这些沉积物的液化反应的后果是很高的。例如，最近对新西兰霍克湾地区(纳皮尔和黑斯廷斯)的液化危险研究预测，设计事件将出现严重液化。同样，对荷兰北部一段堤坝进行的一项研究也预测了高度的液化风险。在这两种情况下，预计将严重液化的矿藏与新西兰克赖斯特彻奇的矿藏具有相似的特征，这突显了目前使用的评估程序的局限性。因此，政府监管机构面临着这样一个问题：根据这些研究，是否应该花费有限的资源，可能/可能是不必要的，以减轻感知到的液化风险(例如，荷兰只有一段堤坝的修复成本估计为约1亿美元，修复该地区所有堤坝的成本可能超过10亿美元)。相反，如果对液化风险研究的结果不屑一顾，后果可能会更严重，而且这些矿床在受到未来地震的震动时，确实容易受到严重液化的影响。与霍克湾、克赖斯特彻奇和荷兰类似的挑战土壤的地点在美国和世界各地都很普遍。为了了解当前工程模型缺陷的根本原因，将从新西兰克赖斯特彻奇具有挑战性的土壤场地提取大片垂直土层，工程模型准确地和不准确地预测液化的严重程度。这些剖面中是否存在深层液化的证据将通过检查这些“地质切片”来确定，这使我们能够确定当前模型的问题是否与预测液化发生有关，或者该问题是否与预测地面液化表现的严重程度有关。此外，还将详细记录这些土壤剖面的特性。将开发新的、先进的识别剖面类型的工具，并与修订的工程模型一起使用，以准确预测未来地震中液化的发生和严重程度。来自弗吉尼亚理工大学和密歇根大学的两名博士生将与新西兰奥克兰大学和新西兰坎特伯雷大学的新西兰留学生合作开展这一项目。该项目的首席调查员已经为退伍军人建立了一个外联方案，并将利用该项目进一步努力与退伍军人合作。2010-2011年新西兰坎特伯雷地震序列(CES)期间，在具有挑战性的土壤场地(例如，夹层粉土和粘土层的沙质土壤沉积物)的地表液化表现的预测和观测严重程度的比较，突出了目前用于评估这些沉积物的液化响应的程序的重大局限性。当前程序的潜在问题包括常用场地表征技术的局限性，以及评估深层液化触发与表面液化表现的严重程度之间的区别，后者已被证明与损害潜力相关。不能准确预测这些沉积物的液化反应的后果是很高的。因此，这项研究将开发一种基于挑战土壤场地的地貌控制与场地表征的新方法的联系来评估挑战土壤场地的液化响应的程序。这项研究将尽可能地利用新西兰最近地震的丰富的现场表现数据，以及来自其他有良好记录的历史液化案例的数据，并将采用？地理切片？以及视锥渗透测试、VisCPT以及更常规的现场和实验室测试。该项目将由来自弗吉尼亚理工大学、密歇根大学和QuakeCoRE：新西兰地震复原力中心(即大学)的研究人员合作完成。来自坎特伯雷大学。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project focuses on improving engineering models for predicting the severity of earthquake-induced liquefaction at "challenging soil sites." Liquefaction is a phenomenon wherein loose, saturated, sandy soils lose their strength during earthquake shaking, leading to significant damage to nearby infrastructure. Field investigations performed following recent earthquakes in Christchurch, New Zealand highlighted the limitations of the current engineering liquefaction severity models for profiles having clay layers interbedded within the liquefiable sandy layers (i.e., "challenging soil sites"); similar geologic profiles are common in the US and worldwide. However, the root cause of the model shortcomings is unknown. The ramifications of not being able to accurately predict the liquefaction response of these deposits are high. For example, a recent liquefaction hazard study for the Hawke's Bay region of New Zealand (Napier and Hastings) predicts severe liquefaction for the design event. Similarly, a study performed for a stretch of levees in the northern portion of the Netherlands also predicts a high liquefaction hazard. In both cases, the deposits that are predicted to severely liquefy have similar characteristics to those in Christchurch, New Zealand that highlight the limitations in currently used evaluation procedures. As a result, government regulators are faced with the question of whether limited resources should be expended, potentially/likely unnecessarily, to mitigate the perceived risk of liquefaction based on these studies (e.g., the remediation cost for only one stretch of levees in the Netherlands is estimated to be ~$100mil, with costs potentially exceeding $1bil to remediate all the levees in the region). On the contrary, the consequences could be even higher if the results of the liquefaction hazard studies are offhandedly dismissed, and the deposits are truly susceptible to severe liquefaction when subjected shaking from future earthquakes. Challenging soil sites similar to those in Hawke's Bay, Christchurch, and the Netherlands are prevalent in regions across the US and worldwide. Towards understanding the root cause of the shortcoming in current engineering models, large vertical slices of soils will be extracted from challenging soil sites in Christchurch, New Zealand where the engineering models accurately and inaccurately predicted the severity of liquefaction. The existence of evidence of the occurrence of liquefaction at depth in these profiles will be determined by examining these "geo-slices," allowing us to determine whether the issue with current models is related to predicting the occurrence of liquefaction or whether the issue is related to predicting the severity of the manifestations of liquefaction at the ground surface. Additionally, the characteristics of these soil profiles will be documented in detail. New, advanced tools for identifying the types of profiles will be developed and used in conjunction with revised engineering models to accurately predicted the occurrence and severity of liquefaction in future earthquakes. Two doctoral students from Virginia Tech and the University of Michigan will work on this project, in collaboration with New Zealand-funded students from the University of Auckland and the University of Canterbury, New Zealand. The Principle Investigator for this project has established an outreach program for military veterans and will use the project to further his efforts of working with veterans. Comparison of predicted versus observed severity of surficial liquefaction manifestations at "challenging" soil sites (e.g., sandy soil deposits with interbedded silt and clay layers) during the 2010-2011 Canterbury, New Zealand earthquake sequence (CES) highlights significant limitations in currently used procedures for evaluating the liquefaction response of these deposits. The potential issues with current procedures include limitations in commonly used site characterization techniques and distinguishing between evaluating liquefaction triggering at depth versus severity of surficial liquefaction manifestations, where the latter has been shown to correlate with damage potential. The ramifications of not being able to accurately predict the liquefaction response of these deposits are high. Accordingly, this research will development a procedure to evaluate the liquefaction response of challenging soil sites based on the linkage of geomorphological controls of challenging soil sites and novel approaches for site characterization. This study will exploit to the extent possible the wealth of field performance data from recent earthquakes in New Zealand, as well as data from other well-documented historic liquefaction case histories, and will employ ?geo-slicing? and Vision Cone Penetration Tests, VisCPT, as well as more conventional field and laboratory testing. The project will be performed collaboratively by researchers from Virginia Tech, University of Michigan, and QuakeCoRE: New Zealand Centre for Earthquake Resilience (i.e., Univ. of Canterbury, Univ. of Auckland, and Tonkin + Taylor Ltd).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.