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

知识专长：许多用于评估液化的常用程序主要基于对干净砂或具有有限量细粒的砂的现场和实验室测试。 例如，广泛使用的Seed等人（1985年）基于标准贯入试验的相关性的土壤崩解触发数据库仅包含13个涉及含有大量细粒（即35%细粒）的土壤的案例。 Youd等人（2001）的最新液化评价文件和设计指南通常使用“中国标准”来识别易液化的土壤。 例如，“加州液化危害分析和缓解指南”（Martin和Lew，1999年）指出，“粘性土是指粘土含量（粒径0.005 mm）大于15%的土壤”，以及“如果在现场勘探期间遇到粘性土材料，则这些材料可能被视为不可液化。“然而，最近地震后的研究已经确定了大量的情况下，在含有超过15%的粘土颗粒的细粒土壤地面故障造成重大的建筑物损坏。 例如，Bray等人（2001年）发现，土耳其阿达帕扎里淤泥中的液化和地面软化是造成该市大部分破坏的原因。 这些粉质土的粘粒含量通常大于15%。 最近完成的Ada-pazari（Bray等人，2004）中仔细回收的土样的循环三轴试验证实，具有高粘土含量的低塑性粉土在严重的地震荷载下会发生破坏。这些土壤的反应比干净的沙子更不容易理解。 本研究是对粉质和粘性土液化敏感性的重新评估，并提供了基于矿物学的细粒土动力响应的见解，本研究的主要目标是评估具有显著细粒（塑性和非塑性）的土的循环响应。 需要对这些土进行先进的循环试验，以表征细粒土的液化敏感性，评估其抗液化性，并了解其液化后的响应（即体积应变和残余强度）。 循环简单剪切试验，与一些互补的循环扭转剪切和循环三轴试验进行比较，正在进行的粉质和粘性土，以前从阿达帕扎里，土耳其收回。 这些土壤具有代表美国许多细粒土壤的一系列土壤特性。使用湿土以统一的方式制备样品，以便样品反应反映自然沉积的土壤，但没有自然土壤沉积物的固有变化。 对于相当均匀的土样，可以系统地评估通过测试天然土的“未扰动”土样无法隔离的重要效应，例如土塑性、孔隙比、围压、初始静驱动应力、超固结比和围压时间的效应。循环试验的结果将有助于重新定义细粒土的液化敏感性。 对易液化土壤的筛选是评价液化危害的第一步。 近期地震现场观测的初步结果和细粒土“未受扰动”样本的试验结果表明，工程专业目前将易液化的土壤归类为“不可液化”。" 更广泛的影响：加州的《地震灾害测绘法》和其他相关工作的实施主要基于经验方法，需要随着重要案例的出现而重新评估和更新，例如土耳其阿达帕扎里的建筑物因粉质和粘性土壤液化和软化而遭到破坏。 从这项研究中可以学到重要的教训，因为在这项研究项目中调查的土壤和地震震动的强度代表了美国的控制地震危险之一（即接近大规模地震的贫瘠土壤）。 非塑性粉土和微塑性粘性粉土的响应远不如净砂的响应那么令人了解，而且，涉及具有显著细粉的土壤的固结触发数据库包含的案例历史相对较少。 本研究允许重新评估用于确定粉质和粘性土液化敏感性的实践状态“中国标准”（由Youd等2001重新采纳）。 它还补充了许多以前的现场，实验室和液化触发和液化的后果，如地面故障及其对结构的影响分析研究。

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.