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Studies of deformation of composite breakwaters under earthquake shaking

地震作用下复合防波堤变形研究

基本信息

批准号：
08555123
负责人：
SEKIGUCHI Hideo
金额：
$ 3.26万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

项目摘要

This research focused on the deformation mechanism of composite breakwaters resting on sandy deposits under conditions of earthquake shaking. Specifically, two interrelated approaches were made. First, a comprehensive set of centrifugal earthquake shaking tests were performed on composite breakwaters that rested on deposits of sand. The relative density of the foundation soil was varied over a wide range, while the intensity of earthquake shaking was held constant. All of the centrifuge tests were carried out under a steady-state centrifugal acceleration of 30 gravities. Viscous scaling was introduced so as to match the time scaling laws of vibration and consolidation. In fact, each centrifuge model was subjected to 20 cycles of sinusoidal excitation, with a peak acceleration of 3 gravities. The experimental results indicated that the caisson structure resting on a loosely packed sand layr underwent an S/D ratio (ratio of settlement S to sand thickness D) as high as 30%. With increased relative density of the supporting sand layr, the S/D ratio of the caisson decreased almost linearly with increasing relative density, realizing an S/D ratio of 3% when the supporting sand layr densified to a relative density of 81%. It is noteworthy that the seismic instability of the foundation soil was a form of repeated bearing-capacity failure, although the soil in the free field or well away from either toe of the rubble mound underwent liquefaction.The second approach was concerned with the development of a finite-element code that permitted a systematic dynamic analysis of the nonlinear seismic behavior of saturated granular soil under earthquake shaking. The theoretical formulations, the related finite-element formulations and the developed source program are described in detail in the final report of this research.

研究了地震作用下桑迪沉积物上复合防波堤的变形机理。具体而言，提出了两种相互关联的办法。首先，一套全面的离心地震震动试验进行了复合防波堤，休息的沉积物的沙子。地基土的相对密度在很大范围内变化，而地震震动强度保持不变。所有离心机测试均在30个重力的稳态离心加速度下进行。为了与振动和固结的时间标度律相匹配，引入了粘性标度。事实上，每个离心机模型都经历了20个周期的正弦激励，峰值加速度为3个重力。试验结果表明，在松散砂层上的沉箱结构沉降S/D比（沉降S与砂层厚度D之比）高达30%。随着支撑砂层相对密度的增加，沉箱的S/D比随相对密度的增加几乎呈线性下降，当支撑砂层密实到相对密度为81%时，S/D比为3%。值得注意的是，地基土的地震失稳是一种重复承载能力失效的形式，尽管自由场地或远离碎石堆趾的土壤发生液化。第二种方法涉及有限元代码的开发，该代码允许对地震震动下饱和颗粒土的非线性地震行为进行系统的动态分析。在本研究的最后报告中详细描述了理论公式、相关有限元公式和开发的源程序。