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筋地基抗震设计概念，用于降低软弱地基上强烈地面震动的强度。这项研究包括离心机和振动台试验以及数值模拟，以证明在格子网格中安装刚性土搅拌板可以减少通过软土剖面的地震能量放大。在大多数情况下，这种地基加固用于增加承载支撑、限制永久变形和/或减少液化潜力。其他好处，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，在目前的设计规定中没有考虑到。这种减少地面震动的做法可以带来更安全、更经济的设计。这项详细的研究利用了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的模型试验，以演示加筋几何形状和布局、刚度比、土层分层和土层特性以及其他因素的影响。先进的三维非线性有限元模型将被用来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史无前例的地面改善设计方法，以减少地面地面运动和对地震易损性土壤场地结构的基础输入。该项目的数据将被存档，并通过NEES项目仓库/数据储存库(http://www.nees.org).The)向公众提供。通过对地震破坏模式的观察，充分证实了结构破坏与当地地质和土壤条件密切相关。柔软、脆弱的网站通常比僵硬的网站表现更差。这是因为软场地往往会放大地面震动的强度，并经常发生大变形，从而导致重大的结构破坏。通过加固和有效加固这些场地，可以显著降低地震破坏的可能性。初步研究表明，将水泥与软土混合，在地面形成坚硬的水泥土面板(即深层土壤搅拌)。对于这样的目的，可以是一种有效的地基加固技术。因此，可以将软土场地改造成像刚性场地一样的行为，从而大大降低地震易损性。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基加固技术的有效性，并开发实用、经济的设计方法。这项工作有可能改善建筑性能，增加安全裕度，并降低地震多发地区的开发成本。这些发现不仅对工程界有影响，而且对企业主、开发商、社区和其他利益相关者也有影响。因此，有一个完善的计划，通过与国家建筑科学研究所(NIBS)、深基础研究所(DFI)和土壤改良承包商在这项研究上的合作，将知识转化为实践。结果还将通过会议、期刊、项目网站传播，并被纳入学术课程和专业课程，供美国土木工程师学会(ASCE)、联邦紧急事务管理局(FEMA)、联邦能源管理委员会(FERC)和美国陆军工程兵部队等团体使用。还有一项积极的外联计划，让以本科生和少数族裔为主的学校以及K-12区学校的学生参与进来。该奖项是国家减少地震灾害计划(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).