NEESR-II: Evaluation of Seismic Levee Deformation Potential by Destructive Cyclic Field Testing

萨克拉门托-圣华金三角洲堤坝是加州S供水系统的重要组成部分。三角洲为加利福尼亚州南部和中部以及旧金山湾区东部的2200万人提供淡水，并直接支持加利福尼亚州每年4000亿美元的经济活动。岛屿？以堤网为界，一般在海平面以下3至5米，涨潮时只有约1至1.5米的干舷保护。堤坝的决口导致水道中的水流入该岛，从而淹没了农田和野生动物栖息地，并将咸水从旧金山湾引入三角洲。这可能是一种灾难性的情况，因为盐水污染可能会导致加州中部和南部的供水中断，使许多社区失去唯一的水源。这种情况不太可能发生在由穴居动物和其他当地危险造成的个别堤坝决口的情况下，因为现有的应急响应系统可以在几个小时内对单个决口做出反应，并在几周内影响修复。另一方面，地震风险是一个非同寻常的威胁，因为可能会有多个同时发生的破坏淹没三角洲内的许多岛屿。据预测，这种大范围的系统故障将导致长达28个月的时间，在此期间，三角洲地区的淡水输送将无法实现。事实上，一些人质疑这样的一系列违规行为是否会永久性地改变地区格局，以至于要么需要寻找替代水源，要么需要重新配置或重新安置加州经济/人口的主要部门。地震震动对堤坝行为的影响是不确定的，因为下面的泥炭有机土壤的循环变形潜力还没有被很好地了解，而且迫切需要研究这些材料的行为。智力价值和范围：该奖项将支持对现有土堤(在几何上非常类似于堤坝，但目前不含水)的全面测试，以研究现实应力和边界条件下泥炭有机地基的原位变形潜力。测试条件和仪器将被设计用来测量可能导致干舷严重损失并导致破裂的变形机制。这类数据对于开发更合理的分析工具以评估堤坝的地震脆弱性至关重要。现场测试将得到广泛的实验室测试计划的补充，以进一步调查关键材料的响应特性，如因震动而导致的土壤强度损失和体积减少。对堤防地震易损性的改进知识将广泛适用于任何建立在有机土壤上的土结构。测试活动将与加州水资源部的工程师密切协调，以确定合适的地点。从这个项目中获得的见解可能会从根本上改变三角洲地震风险评估和改造决策的方式。更广泛的影响：这项研究最重要的社会影响将是改进三角洲地区的地震风险评估，这反过来将导致更知情的改造和/或建设决策，以及更有可能在地震期间和之后维持功能的供水系统。该奖项还将支持开发教育模块，以利用NEES资源为更广泛的NEESincc教育、外联和培训目标(EOT)做出贡献。这些单元将讲授当前的供水系统、三角洲地区的堤坝网络、供水与堤防网络之间的联系、这些堤坝的工程特性、堤坝潜在的地震破坏机制以及对饮用水和灌溉用水供应的影响。这些单元将包括一份学习指南，其中载有关于在不同级别(即本科生和K-12)实施这些单元的建议。该项目的数据将通过NEES数据库(http://www.nees.org))提供

The Sacramento-San Joaquin Delta levees are critical components of California?s water distribution system. The Delta supplies fresh water to 22 million people in southern and central California as well as eastern portions of the San Francisco Bay area and directly supports $400 billion/year of economic activity within the State of California. The ?islands? circumscribed by the network of levees are commonly 3 to 5 meters below sea level, and are protected by only about 1 to 1.5 meters of freeboard at high tide. A breach in a levee causes water from the channel to flow into the island thereby inundating farmland and wildlife habitat, and drawing saline water from the San Francisco Bay into the Delta. This is a potentially catastrophic scenario, as saline contamination could halt water delivery to central and southern California, removing the sole water source for many communities. This scenario is unlikely in the event of an individual levee breach caused by burrowing animals and other local hazards because the existing emergency response system can respond to a single breach within a matter of hours and affect repair within a matter of weeks. On the other hand, seismic hazard is an extraordinary threat because of the potential for multiple simultaneous breaches inundating many islands within the Delta. Such widespread system failure has been forecast to cause up to 28 months of time during which fresh water deliveries from the Delta would not be possible. Some in fact question whether such a sequence of breaches might permanently change the regional morphology such that either alternative water sources would need to be identified or major sectors of the California economy/population would need to be reconfigured or relocated. The influence of earthquake shaking on the behavior of the levees is uncertain because the cyclic deformation potential of the underlying peaty organic soils not well understood, and there is an urgent need to investigate the behavior of these materials.Intellectual Merit and Scope: This award will support full-scale testing of an existing earth embankment (very similar in geometry to a levee, but not currently holding water) to investigate the in situ deformation potential of peaty organic foundation soils under realistic stresses and boundary conditions. The test conditions and instrumentation will be designed to measure the deformation mechanisms that can result in a critical loss of freeboard leading to a breach. Data of this sort is essential for the development of more rational analysis tools for assessing the seismic vulnerability of levees. The field testing will be supplemented by an extensive laboratory testing program to further investigate key material response characteristics such as soil strength loss and volume reduction caused by shaking. The improved knowledge of levee seismic vulnerability will be broadly applicable wherever these earth structures are founded on organic soils. Testing activities will be closely coordinated with engineers at the California Department of Water Resources to identify a suitable site. Insights gained from this project could fundamentally alter the manner in which Delta seismic risk is assessed and retrofit decisions are made. Broader Impacts: The most important societal impact of this research will be improvement of seismic risk assessment in the Delta, which in turn will result in better informed retrofit and/or construction decisions and a water delivery system that is more likely to maintain functionality during and following earthquake shaking. This award will also support development of education modules that leverage NEES resources to contribute to the broader NEESinc goals for education, outreach and training (EOT). The modules will teach about the current water delivery system, the network of levees in the Delta, the link between water delivery and the levee network, the engineering properties of these levees, the potential seismic failure mechanisms of the levees, and the consequences on the availability of water for drinking and irrigation. Included with the modules will be a study guide containing suggestions regarding implementation of the modules at different levels (i.e., undergraduates and K-12). Data from this project will be made available through the NEES data repository (http://www.nees.org)