NEESR: Reduction of Seismic Shaking Intensity on Soft Soil Sites Using Stiff Ground Reinforcement

该项目的主要目标是开发一种新的加固地基抗震设计概念，用于降低软场地强烈震动的强度。这项研究包括离心机和振动台测试以及数值模拟，以证明安装在格子型网格中的刚性混合土板可以减少地震能量通过软土剖面的放大。在大多数情况下，这种地面加固用于增加轴承支撑，限制永久变形和/或减少液化潜力。额外的好处，如有利地改变土壤剖面的动态传递函数，从而减少输入上部结构的震动水平，在当前的设计规定中没有考虑到。这种地面震动的减少可以导致更安全、更经济的设计。这项详细的研究利用加州大学戴维斯分校的离心机设备和加州州立大学富勒顿分校的振动台进行模型试验，以证明钢筋几何形状和布局、刚度比、土壤剖面的分层和性质以及其他因素的影响。先进的三维非线性有限元建模将用于将模型试验结果外推到广泛的现场和现场条件，以便开发设计曲线。这项工作代表了一种前所未有的方法来设计地基改善，以减少地面地面运动和基础输入到地震脆弱的土壤站点的结构中。该项目的数据将存档，并通过NEES项目仓库/数据库（http://www.nees.org）.The)向公众提供。减轻软土场地的地震破坏潜力仍然是地震工程中的主要挑战之一。通过对地震破坏模式的观察，结构破坏与当地地质和土壤条件密切相关。软的、弱的网站通常比硬的网站更糟糕。这是因为软场地往往会放大地面震动的强度，并经常经历可能导致重大结构损坏的大变形。通过加强和有效加固这些地点，可以大大减少地震破坏的可能性。初步研究表明，将水泥与软土混合，在地面上形成坚硬的水泥土板(即？深层土壤混合是一种有效的地面加固技术。因此，软土场地可以转变为刚性场地，从而大大降低地震易感性。该项目围绕物理和分析建模的综合计划进行组织，以调查和验证各种地面加固技术的有效性，并开发一种实用、经济的设计方法。这项工作有可能改善地震易发地区的建筑性能，增加安全边际，并降低开发成本。这些发现不仅对工程社区有影响，而且对业务所有者、开发人员、社区和其他涉众也有影响。因此，通过与国家建筑科学研究所（NIBS）、深地基研究所（DFI）和合作进行这项研究的土壤改善承包商的合作，有一个完善的将知识转化为实践的计划。研究结果还将通过会议、期刊、项目网站发布，并纳入学术课程和专业短期课程，供美国土木工程师学会（ASCE）、联邦紧急事务管理局（FEMA）、联邦能源监管委员会（FERC）和美国陆军工程兵团等团体使用。还有一个积极的外展计划，让主要来自本科生和少数民族服务机构的学生以及来自地区K-12学校的学生参与进来。该奖项是国家减少地震危害计划（NEHRP）的一部分。

The primary objective of this project is to develop a new seismic design concept for reinforced ground that can be used to reduce the intensity of strong ground shaking on soft sites. The study involves centrifuge and shake table testing as well as numerical modeling to demonstrate that stiff soil-mix panels, installed in lattice-type grids, can reduce the amplification of seismic energy up through soft soil profiles. In most cases, such ground reinforcement is used to increase bearing support, limit permanent deformations, and/or reduce liquefaction potential. Additional benefits, such as favorably altering the dynamic transfer function of the soil profile and thereby reducing the shaking levels input into the superstructure are not considered in current design provisions. Such reductions in ground shaking can lead to safer and more economical designs. This detailed study utilizes model testing with the centrifuge facility at the University of California Davis and a shake table at California State University Fullerton to demonstrate the effects of reinforcement geometry and layout, stiffness ratio, layering and properties of the soil profile, and other factors. Advanced three-dimensional nonlinear finite element modeling will be used to extrapolate the model test results to a wide range of field and site conditions so that design curves can be developed. This work represents an unprecedented approach to design ground improvement to reduce surface ground motions and base input into structures at seismically vulnerable soil sites. Data from this project will be archived and made available to the public through the NEES Project Warehouse/data repository (http://www.nees.org).The mitigation of the earthquake damage potential of soft soil sites remains one of the leading challenges in earthquake engineering. It is well-established through observations of earthquake damage patterns that structural damage is strongly correlated with local geological and soil conditions. Soft, weak sites generally fare worse than stiff sites. This is because soft sites tend to amplify the intensity of ground shaking and often undergo large deformations that can cause major structural damage. Earthquake damage potential can be significantly reduced by reinforcing and effectively stiffening such sites. Preliminary studies suggest that mixing cement with the soft soils to form stiff soil-cement panels in the ground (i.e., ?deep soil mixing?) can be an effective ground reinforcement technique for such purposes. Therefore soft soil sites can be transformed to behave like stiff sites, thereby greatly reducing earthquake vulnerability. The project is organized around an integrated plan of physical and analytical modeling to investigate and validate the effectiveness of various ground reinforcement techniques and develop a practical, economical design approach. This work has the potential to improve building performance, increase safety margins, and reduce development costs in earthquake prone regions. The findings will have implications not only for the engineering community, but also for business owners, developers, communities, and other stakeholders. As such, there is a well-developed plan for transferring knowledge into practice through partnership with the National Institute of Building Sciences (NIBS), the Deep Foundations Institute (DFI), and soil improvement contractors who are collaborating on this research. Results will be also be disseminated via conferences, journals, the project website, and incorporated into academic courses and professional shortcourses for groups such as American Society of Civil Engineers (ASCE), Federal Emergency Management Agency (FEMA), Federal Energy Regulatory Commission (FERC), and U.S. Army Corps of Engineers. There is also an aggressive outreach plan for the involvement of students from a predominantly undergraduate and minority serving institution, as well as from area K-12 schools. This award is part of the National Earthquake Hazard Reduction Program (NEHRP).