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Seismic Site Response Analysis Considering Partially Saturated Soil Conditions

考虑部分饱和土壤条件的地震场地响应分析

基本信息

批准号：
1333810
负责人：
Majid Ghayoomi
金额：
$ 16.9万
依托单位：
University of New Hampshire
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2013
资助国家：
美国
起止时间：
2013-09-01 至 2016-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1333810&HistoricalAwards=false
关键词：
Seismic Site Response Analysis Considering

项目摘要

The seismic response of partially saturated soils differs from that of dry or water saturated soil deposits. Yet, the available site response analysis methods ignore the influence of partial saturation in the soil. This research will study the effects of partial saturation on the seismic site response analysis and how different suction (degree of saturation) profiles affect the seismic response of a soil layer. Suction due to partial saturation increases the effective stresses acting on the soil, altering the shear modulus, shear wave velocity, nonlinear deformation response, and damping. As a result, the distribution of suction with depth is expected to affect the propagation of seismic waves and the resulting ground accelerations. This, in turn, influences the seismic demand imposed on the soil and surface structures. Although the shear wave velocity employed in current site response analysis methods accounts for partial saturation of the soil, it only reflects the degree of saturation at the time of shear wave velocity measurement. Hence, the seasonal fluctuation of the water table and its impact on degree of saturation may alter the site response. The current state of practice commonly relies on procedures that include dynamic material properties of either water saturated or dry soils as the most conservative scenarios. This might be an appropriate assumption for problems dealing with soils' strength and deformation. However, stiffer partially saturated soils due to inter-particle suction forces result in a higher site natural frequency and lower damping, which may adversely affect the site response. In this study, the steady state-infiltration through an unsaturated soil layer inside a geotechnical centrifuge will be implemented to control the soil layer?s degree of saturation. Cyclic loads with different amplitudes and frequencies, and earthquake motions with different intensities will be applied to the soil layers with various suction profiles. These profiles are controlled by the infiltration rate and the centrifugal acceleration. The experimental data will be compared with the numerically estimated site responses incorporating effective stress-based, suction-dependent dynamic material properties. This research will advance the fundamental knowledge of unsaturated soil dynamics and seismic performance of geotechnical systems by incorporating the effects of seasonal fluctuation of degree of saturation on site response. The work will assist in better understanding of fundamental mechanism of wave propagation through an unsaturated soil layer. This project will be a substantial step towards more sustainable and safer seismic designs of buildings and infrastructure. The potential findings of the project will help in assessing the performance of current approaches in evaluating the seismic site response and provide practical recommendations to consider the partial saturation in current seismic site response analysis methods. The graduate student development will prepare students to lead the profession through advanced technical training in geotechnical earthquake engineering, water infiltration, and physical modeling, as well as mentoring opportunities. The importance of earthquake engineering and seismic hazards will be introduced to college Civil Engineering and K-12 students through undergraduate research, courses, and outreach programs.

部分饱和土壤的地震反应不同于干燥或水饱和土壤沉积物。然而，现有的场地反应分析方法忽略了土壤中的部分饱和的影响。本研究将探讨部分饱和对地震场地反应分析的影响，以及不同的吸力（饱和度）剖面对土层地震反应的影响。由于部分饱和引起的吸力增加了作用在土壤上的有效应力，改变了剪切模量、剪切波速、非线性变形响应和阻尼。因此，吸力随深度的分布预计会影响地震波的传播和由此产生的地面加速度。这反过来又会影响施加在土壤和表面结构上的地震需求。虽然在目前的场地反应分析方法中采用的剪切波速度解释了土壤的部分饱和度，但它仅反映了剪切波速度测量时的饱和度。因此，地下水位的季节性波动及其对饱和度的影响可能会改变场地响应。目前的实践状态通常依赖于包括水饱和或干燥土壤的动态材料特性作为最保守的方案的程序。这可能是处理土的强度和变形问题的适当假设。然而，由于颗粒间吸力导致的较硬的部分饱和土壤会导致较高的场地固有频率和较低的阻尼，这可能会对场地响应产生不利影响。在本研究中，将借由土工离心机内之非饱和土层稳态入渗来控制土层？饱和度。不同振幅和频率的循环荷载以及不同强度的地震运动将施加到具有不同吸力剖面的土层上。这些轮廓由渗透率和离心加速度控制。将实验数据与数值估计的现场响应进行比较，将有效应力为基础的，吸力相关的动态材料特性。通过考虑饱和度的季节性波动对场地响应的影响，本研究将推进非饱和土动力学和岩土系统抗震性能的基础知识。这项工作将有助于更好地理解波在非饱和土层中传播的基本机制。该项目将是朝着更可持续和更安全的建筑物和基础设施抗震设计迈出的重要一步。该项目的潜在研究结果将有助于评估当前方法在评估地震现场反应方面的性能，并为考虑当前地震现场反应分析方法中的部分饱和提供实用建议。研究生的发展将准备学生通过在岩土地震工程，水渗透和物理建模，以及指导机会的先进技术培训，引领行业。地震工程和地震灾害的重要性将通过本科研究，课程和推广计划介绍给大学土木工程和K-12学生。

项目成果

期刊论文数量（9）

专著数量（0）

科研奖励数量（0）

会议论文数量（0）

专利数量（0）

Cyclic Direct Simple Shear Test to Measure Strain-Dependent Dynamic Properties of Unsaturated Sand

DOI：
10.1520/gtj20160128
发表时间：
2017-05-01
期刊：
GEOTECHNICAL TESTING JOURNAL
影响因子：
1.6
作者：
Le, K. N.;Ghayoomi, M.
通讯作者：
Ghayoomi, M.

Simulating Seismic Response of Unsaturated Sand Layers inside a Geotechnical Centrifuge

模拟土工离心机内不饱和砂层的地震响应

DOI：
发表时间：
2017
期刊：
19th International Conference on Soil Mechanics and Geotechnical Engineering
影响因子：
0
作者：
Mirshekari, M. and;Ghayoomi, M.
通讯作者：
Ghayoomi, M.

Suction-Controlled Cyclic Triaxial System for Measurement of Dynamic Properties of Unsaturated Soils

吸力控制循环三轴系统测量非饱和土动力特性