Liquefaction Consequences of Stratified Deposits of Silty Soils

粉质土壤分层沉积物的液化后果

• 批准号: 1561932
• 负责人: Jonathan Bray
• 金额: $ 48.93万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-07-01 至 2021-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1561932&HistoricalAwards=false
• 关键词: Liquefaction; Consequences; Stratified; Deposits; Silty

Soil liquefaction caused significant damage to buildings and lifelines in Christchurch, New Zealand during the 2010-2011 Canterbury Earthquake Sequence. New Zealand design and construction methods are similar to those in the U.S., so lessons learned from these earthquakes are directly transferrable to the U.S. Many of the cases of liquefaction-induced damaged were captured well by current design procedures. However, many other cases were not. The occurrence and effects of soil liquefaction were over-predicted in several parts of the city that contained silty soil deposits. Most liquefaction case histories and laboratory experiments have focused on the response of clean sands. Silty soils differ from clean sands in several characteristics. Silts contain different sized and shaped particles with different mineralogy. Different depositional processes create silt deposits. Therefore, it should not be surprising that silty soil deposits responded differently than clean sand deposits. Yet, engineers currently rely on design procedures largely based on the seismic performance of clean sands. This practice can result in significant discrepancies between predictions and actual performances at silty soil sites. Thus, there is a pressing need to investigate the seismic response of stratified deposits of silty soils at sites that were strongly shaken and predicted to liquefy during the 2010-11 Canterbury earthquakes but did not exhibit evidence of liquefaction.The over-prediction of liquefaction triggering by current procedures appears to be due to their inability to capture the cyclic response of stratified silty soil deposits. Insight will be gained by investigating the liquefaction triggering of sites with stratified silty soil deposits that conventional procedures indicate should have liquefied, but field observations indicate did not liquefy. The current hypothesis to evaluate is that an assessment of the soil-water system response of stratified soil deposits is required to capture the observed cases of no liquefaction manifestations. Empirical correlations that relate cone penetration test (CPT) results to the fines content and plasticity of the soil will be evaluated, and the hypothesis that fines content is not a meaningful parameter in deposits of fine sand/coarse silt will be tested. Through a program of cyclic testing of natural and prepared soil specimens, fundamental insights regarding the cyclic response of silty soils will be developed. A satisfactory understanding of the cyclic response of silty soils is currently lacking. Through validated numerical simulations that capture the nonlinear, effective stress response of stratified silty soil deposits, insights regarding key mechanisms and probable reasons for the lack of manifestations of liquefaction at sites that simplified procedures indicate should have liquefied will be developed. The work will lead to recommendations on how to assess the cyclic response of stratified soil sites which include an alternative liquefaction evaluation method. This grant supports an international research collaboration with New Zealand that will advance knowledge in the U.S. and in New Zealand. The U.S. PhD student, who is targeted to be female, will benefit greatly from participating in this international study. Co-funding of this award has been provided by the NSF Office of International Science and Engineering.

在2010 - 2011年坎特伯雷地震序列期间，土壤液化对新西兰基督城的建筑物和生命线造成了重大破坏。新西兰的设计和施工方法与美国的设计和施工方法相似，因此从这些地震中学到的经验教训可直接转移到美国，许多液化引起的损坏的案例被当前的设计程序很好地捕获了。 但是，许多其他案件却没有。 土壤液化的发生和作用在包含粉质土壤沉积物的城市的几个地区过高了预测。 大多数液化病例的历史和实验室实验都集中在清洁沙子的反应上。 粉质土壤在几种特征上与干净的沙子不同。 淤泥含有不同尺寸和形状的颗粒，具有不同的矿物学。不同的沉积过程会产生淤泥沉积物。因此，不足为奇的是，粉质土壤沉积物的反应与干净的沙子沉积物不同。 然而，工程师目前主要基于清洁砂的地震性能依靠设计程序。这种做法可能会导致预测和粉质土壤部位的实际表现之间存在很大差异。 因此，需要调查在2010 - 11年度坎特伯雷地震期间强烈动摇并预测液化的地点分层沉积物的地震反应，但没有表现出液化的证据。根据当前的程序，似乎是由于它们无法捕获分层粉质土壤沉积物的循环反应。 通过研究具有分层粉质土壤沉积物的地点的液化触发，传统手术表明应该液化，但现场观察表明，将获得洞察力。 当前评估的假设是，需要评估分层土壤沉积物的土壤系统反应，以捕获未观察到的没有液化表现的病例。 将评估将锥体渗透测试（CPT）与土壤的罚款含量和可塑性相关联的经验相关性，并且将测试罚款含量是罚款含量不是有意义的参数的假设。 通过对天然和准备好的土壤标本的循环测试计划，将开发有关粉质土壤环境反应的基本见解。 目前缺乏对粉质土壤的循环反应的满意理解。 通过经过验证的数值模拟捕获分层土壤沉积物的非线性，有效的应力反应，有关关键机制的见解以及可能在简化程序表明应该已经液化的地点缺乏液化表现的可能原因。这项工作将导致有关如何评估分层土壤位点的循环响应的建议，包括替代性液化评估方法。 该赠款支持与新西兰的国际研究合作，该研究将推进美国和新西兰的知识。 目标是女性的美国博士学位学生将从参加这项国际研究中受益匪浅。 NSF国际科学与工程办公室已提供了该奖项的共同资助。