NEESR: Levees and Earthquakes: Averting an Impending Disaster

萨克拉门托/圣华金三角洲是加州供水系统的枢纽，为2000多万人提供服务，是许多独特的濒危/受威胁物种的家园，也是肥沃的农田。 它由大约1100英里的堤坝包围的“岛屿”组成，堤坝不断蓄水，防止岛屿被洪水淹没。 在过去的150年里，构成三角洲大部分地区的泥炭有机土壤已经氧化并被吹走，导致快速沉降，许多岛屿现在低于海平面3至5米。 堤坝由饱和的未压实松散疏浚土组成，因此容易发生液化。 三角洲位于圣安德烈亚斯断层系统的东部边缘，处于中等地震危险区。 最近的预测表明，三角洲地震可能会导致大范围的堤坝破坏和多个岛屿同时被淹没。 这样的事件将在当地扭转三角洲的水流方向，导致盐水从西部侵入，污染供水，并停止供水数年。 该奖项的研究目标是调查泥炭质有机土壤上可液化堤坝的变形潜力。 模型堤坝将由类似于三角洲堤坝填料的土壤建造，并将建立在从三角洲挖掘的泥炭有机土壤上。 这些模型将在土工离心机上建造，使小规模模型能够表现得像一个更大的原型。 将在堤坝的一侧引入水，并在测试之前使其达到稳定状态的渗透条件。 在真实的地震中记录的地面运动的比例版本将被施加在离心模型的基础上。 数百个传感器将嵌入模型中，以记录加速度、孔隙水压力和变形，从而能够准确描述堤坝的反应以及地震能量在不同土层中的传输。 该项目的数据将通过NEES项目仓库数据库存档并向公众提供http://www.nees.org.The三角洲地震情景是美国面临的最重要的危险之一，因为考虑到三角洲水是许多农业社区的唯一来源，并构成城市供水的重要组成部分，这种事件的后果将是无可避免的灾难性的。 科学界的共识是，三角洲地震的情况是一个重大的威胁，但许多三角洲的土地所有者和当地的工程师认为，地震的威胁是一个恐吓战术所创造的特殊利益，以证明建设一个替代输水系统，绕过三角洲。 他们对科学界的不信任在很大程度上源于对液化危害缺乏了解，迫切需要向立法者有效和明确地传达风险。 通过该奖项进行的测试视频将提供一个很好的教育工具，以证明地震对可液化堤坝填料的影响。 建议工作的主要教育目标是帮助建议的重要决定，目前正在作出关于加州的水分配系统。 研究小组由PI斯科特J布兰登伯格（加州大学洛杉矶分校），共同PI的乔纳森P斯图尔特（加州大学洛杉矶分校）和安妮莱姆尼策（加州大学欧文分校），和高级人员乔治Mylonakis（美国）。Patras）。 该研究将利用乔治E.小布朗加州大学戴维斯分校的地震工程模拟网络（NEES）设施。 该奖项是国家减少地震灾害计划（NEHRP）的一部分。

The Sacramento / San Joaquin Delta, the hub of California's water delivery system that serves over 20 million people, is home to many unique endangered/threatened species, and is rich farmland. It is composed of "islands" circumscribed by approximately 1100 miles of levees that constantly impound water, preventing flooding of the islands. Peaty organic soils that comprise much of the Delta have oxidized and blown away over the past 150 years, resulting in rapid subsidence and many islands are now 3 to 5 meters below sea level. The levees are composed of uncompacted loose dredged soils that are saturated, and are therefore susceptible to liquefaction. The Delta lies on the eastern margin of the San Andreas fault system in a zone with moderate seismic hazard. Recent projections indicate that a Delta earthquake could result in widespread levee failures and simultaneous inundation of multiple islands. Such an event would locally reverse the flow direction in the Delta, causing intrusion of saline water from the west that would contaminate the water supply and halt water delivery for a period of years. The research objective of this award is to investigate the deformation potential of liquefiable levees supported on peaty organic soils. Model levees will be constructed from soils that are similar to Delta levee fills, and will be founded atop peaty organic soil excavated from the Delta. The models will be constructed on a geotechnical centrifuge that enables a small scale model to behave like a much larger prototype. Water will be introduced on one side of the levee and allowed to reach a steady state seepage condition prior to testing. Scaled versions of ground motions recorded during real earthquakes will be imposed on the base of the centrifuge models. Hundreds of sensors will be embedded in the models to record acceleration, porewater pressure, and deformation, to enable accurate characterization of levee response and the transmission of seismic energy through the various soil layers. Data from this project will be archived and made available to the public through the NEES Project Warehouse data repository at http://www.nees.org.The Delta earthquake scenario is one of the most important hazards facing the United States because the consequences of such an event would be unimaginably catastrophic considering that Delta water is the sole source for many agricultural communities and constitutes a significant fraction of urban water supply. Consensus among the scientific community is that the Delta earthquake scenario is a significant threat, but many Delta landowners and local engineers perceive the earthquake threat as a scare tactic created by special interests to justify construction of an alternative water conveyance system that bypasses the Delta. Much of their mistrust of the scientific community stems from a lack of understanding of liquefaction hazard, and there is an acute need to effectively and clearly communicate risk to lawmakers. Video of the testing performed through this award will provide an excellent educational tool to demonstrate the effects of earthquakes on liquefiable levee fills. The primary educational objective of the proposed work is to help advise the important decisions that are currently being made regarding California's water distribution system. The research team consists of PI Scott J. Brandenberg (UCLA), co-PI's Jonathan P. Stewart (UCLA) and Anne Lemnitzer (UC Irvine), and senior personnel George Mylonakis (U. of Patras). The research will utilize the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) facility at UC Davis. This award is part of the National Earthquake Hazards Reduction Program (NEHRP).