Liquefaction Susceptibility, Resistance, and Response of Silty and Clayey Soils

智力优势：许多评估液化的常用程序主要是基于现场和实验室对洁净砂或少量细砂的测试。例如，广泛使用的Seed等人（1985）基于spt相关性的液化触发数据库仅包含13个案例，涉及具有显著细粒（即35%细粒）的土壤。Youd等人（2001年）撰写的最先进的液化评价论文和设计指南通常使用“中国标准”来识别易液化的土壤。例如，“分析和减轻加州液化危害的指导方针”（Martin and Lew 1999）指出，“粘土是指粘土含量（粒径0.005 mm）大于15%的土壤”，“如果在现场勘探过程中遇到粘土材料，这些材料可能被认为是不可液化的。”然而，最近地震后的研究发现，在含有超过15%粘土大小颗粒的细粒土壤中，地面破坏造成了大量的建筑物损坏。例如，Bray等人（2001）发现，土耳其阿达帕扎里（Adapazari）的淤泥液化和地面软化是造成该市大部分破坏的原因。这些粉质土壤的粘土含量通常大于15%。最近完成的Ada-pazari （Bray et al. 2004）精心提取的土壤样本的循环三轴试验证实，高粘土含量的低塑性泥沙在强烈的地震荷载下可以液化。与干净的沙子相比，人们对这些土壤的反应知之甚少。这项研究为粉质和粘性土壤液化敏感性的重新评估提供了急需的条件，并为细粒土壤的矿物学动态响应提供了见解。本研究的主要目的是评估具有显著细粒（塑料和非塑料）的土壤的循环响应。需要对这些土壤进行高级循环试验，以表征细粒土壤的液化敏感性，评估其液化阻力，并了解其液化后响应（即体积应变和残余强度）。循环单剪试验，与一些互补的循环扭剪和循环三轴试验进行比较，正在对先前从土耳其Adapazari提取的粉质和粘土进行试验。这些土壤具有一系列的土壤特征，代表了美国许多细颗粒土壤。采用湿法以统一的方式制备标本，使标本反应反映自然沉积的土壤的反应，但没有自然土壤沉积的固有变异性。在相当均匀的土样条件下，可以系统地评价土壤塑性、孔隙比、围应力、初始静态驱动应力、超固结比、约束时间等重要影响，而这些影响是通过测试“未受干扰”的天然土样无法孤立出来的。这一循环试验方案的结果将有助于重新定义细粒土的液化敏感性。筛选易液化的土壤是评估液化相关危害的第一步。最近地震现场观察的初步结果和对“未受干扰”的细粒土壤样本的测试结果表明，工程专业目前将易液化的土壤分类为“不可液化”。更广泛的影响：加州地震灾害测绘法的实施和其他相关工作主要基于经验方法，随着重要历史案例的出现，需要重新评估和更新，例如土耳其阿达帕扎里（Adapazari）的建筑物因粉质和粘土的液化和软化而遭到破坏。从这项研究中可以学到重要的经验教训，因为该研究项目所调查的土壤和地震震动强度代表了美国控制地震危害的一种（即靠近大地震的贫瘠土壤）。非塑性泥沙和轻度塑性粘土泥沙的响应明显比清洁砂的响应少得多，液化触发数据库包含相对较少的案例历史，涉及具有显着细粒的土壤。这项研究允许对确定粉质和粘性土壤液化敏感性的实践状态“中国标准”进行重新评估（Youd等人于2001年重新采用）。它还补充了以前许多关于液化触发和液化后果的现场、实验室和分析研究，例如地面破坏及其对结构的影响。

INTELLECTUAL MERIT: Many of the commonly used procedures for evaluating liquefaction are largely based on field and laboratory testing of clean sands or sands with a limited amount of fines. For example, the liquefaction-triggering database of the well-used Seed et al. (1985) SPT-based correlation contains only 13 cases involving soils with significant fines (i.e. 35% fines). The state-of-the-art lique-faction evaluation paper by Youd et al. (2001) and design guidelines commonly use the "Chinese Criteria" for identifying soils susceptible to liquefaction. For example, "Guidelines for Analyzing and Mitigating Lique-faction Hazards in California" (Martin and Lew 1999) states, "clayey soils are those that have clay contents (particle size 0.005 mm) greater than 15 percent," and "If clayey soil materials are encountered during site ex-ploration, those materials may be considered non-liquefiable." However, research following recent earthquakes has identified a large number of cases where ground failure in fine-grained soils containing more than 15% clay-size particles caused significant building damage. For example, Bray et al. (2001) found that liquefaction and ground softening in the silts of Adapazari, Turkey were responsible for much of the damage observed in this city. These silty soils typically had clay contents greater than 15%. Recently completed cyclic triaxial testing of carefully retrieved soil specimens from Ada-pazari (Bray et al. 2004) confirm that low plasticity silts with high clay contents can liquefy under severe seis-mic loading. The response of these soils is less understood than that of clean sands. This research is ena-bling a much-needed re-evaluation of the liquefaction susceptibility of silty and clayey soils and provid-ing insight regarding the dynamic response of fine-grained soils based on their mineralogy.The primary goal of this study is to assess the cyclic response of soils with significant fines (both plastic and non-plastic). The advanced cyclic testing of these soils is required to characterize the liquefac-tion susceptibility of fine-grained soils, to evaluate their liquefaction resistance, and to gain insight regard-ing their post-liquefaction response (i.e. volumetric strain and residual strength). Cyclic simple shear test-ing, with some complementary cyclic torsional shear and cyclic triaxial testing for comparison, are being performed on the silty and clayey soils that were previously retrieved from Adapazari, Turkey. These soils possess a range of soil characteristics that represent many fine-grained soils in the United States.Specimens are being prepared in a uniform manner using wet-pluviation so that the specimen re-sponse reflects that of soils deposited in nature but without the inherent variability of natural soil deposits. With fairly uniform soil specimens, important effects that could not be isolated by testing "undisturbed" specimens of natural soils, such as the effects of soil plasticity, void ratio, confining stress, initial static driving stress, overconsolidation ratio, and time under confinement, can be systematically evaluated. The results of this program of cyclic testing will help redefine the liquefaction susceptibility of fine-grained soils. The screening for soils susceptible to liquefaction is the first step in evaluating the hazards associated with liquefaction. Preliminary findings from field observations from recent earthquakes and re-sults from tests on "undisturbed" specimens of fine-grained soils indicate that the engineering profession is currently classifying soils that are susceptible to liquefaction as "non-liquefiable." BROADER IMPACTS: The implementation of California's Seismic Hazards Mapping Act and other related efforts are largely based on empirical methods that require re-evaluation and updating as important case histories emerge, such as the devastation of buildings in Adapazari, Turkey due to liquefaction and softening of silty and clayey soils. Critical lessons can be learned from this study, because the soils and intense level of earthquake shaking investigated in this research project represent one of the controlling earthquake hazards in the U.S. (i.e. poor soils close to large magnitude earthquakes). The responses of non-plastic silts and slightly plastic clayey silts are significantly less understood than that of clean sands, and the liquefaction-triggering database contains relatively few case histories involving soils with signifi-cant fines. This research allows for a re-evaluation of the state-of-the practice "Chinese criteria" for de-termining the liquefaction susceptibility for silty and clayey soils (readopted by Youd et al. 2001). It also complements numerous previous field, laboratory, and analytical studies of liquefaction triggering and the consequences of liquefaction, e.g. ground failure and its effects on structures.