Unexpected Cyclic Deformation of Fine-Grained Soils and Demonstrated Effectiveness of Soil Improvement

在1999年Kocaeli地震（M7.4）期间，土耳其家乐福购物中心的饱和粉土和粘土发生了意想不到的强度损失和软化。该地点距离断裂断层约5公里，下面是软粘土、粉砂和可液化砂。地震发生时，施工正在进行中，主楼下面的土壤已经用紧密间隔的喷射灌浆柱进行了改善。大部分场地仍在未经改良的土壤上。地震发生后，对现场进行了检查，以记录现场表现。震后检查发现，喷浆区域没有沉降，而未改善的部分和邻近未经处理的建筑工地通常有10-12厘米的沉降。此外，令人惊讶的是，大多数定居点发生的未经处理的地区主要由粘土组成，根据目前的工程指导方针，这些土壤被归类为“不可液化”。这些发现表明，目前的工程指南并不能可靠地预测粉质和粘土的地震易感性——这是一种不保守的实践状态。本研究的目的是评估喷射灌浆柱缓解液化效果的主要机制，并研究粉质和粘性土的液化行为。这项工作将包括高质量的土壤取样、实验室测试和数值模拟，以充分解释实地观测结果。大约18次循环单剪试验，18次循环三轴试验和18次静态三轴试验将在土耳其未受干扰的粘土样品上进行。在第一年的早期，需要在土耳其进行为期10天的实地采样，土壤样本将被运回美国。动力实验室试验将用于检查土壤的地震行为，看看现场行为是否可以复制和解释。数值分析将涉及三维有限元模型，模拟现场处理和未处理部分的动态响应。有限元代码DYNAFLOW和OPENSEES将在此工作中使用。这些结果将用于更好地理解为什么喷射注浆截面在减轻损害方面是有效的，例如可能降低土体中的地震剪应力和应变。研究团队是多元化的，包括少数民族，残疾人，高级和初级教师，国际参与者，行业顾问和本科生。该团队将由dr。弗吉尼亚理工大学的J. Martin和C. Olgun。他们将进行数值分析和一些实验室测试。瓦尔帕莱索大学（Valparaiso University）本科学院的C. Polito博士将进行大部分实验室测试。来自土壤改良承包商的顾问将担任顾问角色，包括总工程师A. Sehn博士、Hayward Baker博士和Zetas公司总裁T. Durgunoglu博士。弗吉尼亚理工大学名誉教授J. Mitchell博士也将担任项目顾问。就更广泛的影响而言，这项研究代表了一个前所未有的学习机会，可能对工程实践产生重要影响。这项研究提供了学习新的和有价值的工程经验的机会，这些经验将导致更安全、更经济的基础设施。结果将提交给期刊，并纳入ASCE， FEMA等学术课程和专业工程短期课程。

Unexpected strength loss and softening occurred in saturated silts and clays at the Carrefour Shopping Center in Turkey during the 1999 Kocaeli Earthquake (M7.4). The site is about 5 km from the ruptured fault, and is underlain by soft clays, silts, and liquefiable sands. Construction was ongoing when the earthquake struck, and the soil beneath the main building had been improved with closely-spaced jet-grout columns. Most of the site remained on unimproved soil. Following the earthquake, the site was inspected to document field performance. A post-earthquake inspection found the jet-grouted areas suffered no settlements, whereas the unimproved sections and neighboring untreated building sites commonly suffered settlements of 10-12 cm. Also, surprisingly, the untreated areas where most of the settlements occurred consisted mainly of clayey soils which are classified as "non-liquefiable" by current engineering guidelines. These findings suggest that current engineering guidelines are not reliable predictors of the seismic vulnerability of silty and clayey soils - an unconservative state of practice. The objectives of this research are to evaluate the main mechanism(s) for the effectiveness of the jet-grout columns in mitigating liquefaction, and to investigate the behavior of the silty and clayey soils. The work will involve high-quality soil sampling, laboratory testing, and numerical modeling to fully explain the field observations. Approximately 18 cyclic simple shear, 18 cyclic triaxial, and 18 static triaxial tests will be performed on undisturbed clayey soil samples from Turkey. A 10-day trip involving field sampling in Turkey will be required early the first year, and the soil samples will be shipped back to the US. The dynamic laboratory tests will be used to examine the seismic behavior of the soils to see if the field behavior can be duplicated and explained. The numerical analyses will involve three-dimensional finite element modeling that simulates the dynamic response of the treated and untreated sections of the site. The finite element codes DYNAFLOW and OPENSEES will be used in this effort. These results will be used to better understand why the jet-grouted sections were effective in mitigating damages, such as the possible reduction of seismic shear stresses and strains in the soil mass. The research team is diverse, including an ethnic minority, a disabled person, senior and junior faculty, international participants, industry consultants, and undergraduate students. The team will be led by Drs. J. Martin and C. Olgun of Virginia Tech. They will perform the numerical analyses and some of the laboratory testing. Dr. C. Polito, at Valparaiso University, an undergraduate school, will perform most of the laboratory tests. Consultants from soil improvement contractors will serve in an advisory role, including Dr. A. Sehn, Chief Engineer, Hayward Baker, and Dr. T. Durgunoglu, President, Zetas, Inc. Dr. J. Mitchell, Professor Emeritus at Virginia Tech, will also serve as a project advisor. In terms of broader impact, the study represents an unprecedented learning opportunity that could have important implications for engineering practice. The study presents the opportunity to learn new and valuable engineering lessons that will lead to safer and more economical infrastructure. The results will be submitted to journals and incorporated into academic courses and professional engineering shortcourses for ASCE, FEMA, etc.