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英里长的堤坝包围，这些堤坝不断蓄水，防止岛屿洪水泛滥。构成三角洲大部分地区的泥炭有机土壤在过去150年里被氧化和吹走，导致快速下沉，许多岛屿现在低于海平面3到5米。这些堤坝是由未压实的疏松疏浚土壤组成的，这些土壤是饱和的，因此容易发生液化。三角洲位于圣安德烈亚斯断裂系统的东缘，处于中等地震危险性地带。最近的预测表明，三角洲地震可能导致大范围的堤坝坍塌和多个岛屿同时被淹没。这种情况会在当地逆转三角洲的水流方向，导致来自西部的咸水入侵，污染供水，并在一段时间内停止供水。该奖项的研究目标是调查在泥炭有机土壤上支撑的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充物的土壤建造，并将建立在从三角洲挖掘的泥炭有机土壤之上。这些模型将在土工离心机上建造，使小比例的模型能够像更大的原型一样工作。在测试之前，将在堤坝的一侧引入水，并允许其达到稳定的渗流状态。在真实地震期间记录的地面运动的比例版本将被施加在离心机模型的基础上。数百个传感器将被嵌入到模型中，以记录加速度、孔隙水压力和变形，以便准确描述堤防响应和地震能量在不同土层中的传输。该项目的数据将被存档，并通过http://www.nees.org.The的NEES项目仓库数据库向公众提供。三角洲地震情景是美国面临的最重要的灾害之一，因为考虑到三角洲水是许多农业社区的唯一来源，并且占城市供水的很大一部分，这样的事件的后果将是不可想象的灾难性的。科学界的共识是，三角洲地震的情景是一个重大威胁，但许多三角洲土地所有者和当地工程师认为，地震威胁是特殊利益集团制造的一种恐吓策略，目的是证明建设绕过三角洲的替代供水系统是合理的。他们对科学界的不信任很大程度上源于对液化危险的缺乏了解，迫切需要有效和明确地向立法者传达风险。通过该奖项进行的测试视频将提供一个极好的教育工具，以演示地震对可液化堤坝填充物的影响。拟议工作的主要教育目标是帮助就目前正在做出的关于加州供水系统的重要决策提供建议。研究小组由加州大学洛杉矶分校的Pi Scott J.Brandenberg(加州大学洛杉矶分校)、联合Pi的Jonathan P.Stewart(加州大学洛杉矶分校)和Anne Lemnitzer(加州大学欧文分校)以及高级人员George Mylonakis(帕特拉斯大学)组成。这项研究将利用小乔治·E·布朗。加州大学戴维斯分校地震工程模拟(NEES)设施网络。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).