STUDY ON QUANTITATIVE EVALUATION OF SOIL GROUND DAMPING

本课题的目的是通过理论分析和试验相结合的方法，定量评估地基上的等效刚度系数和粘性阻尼系数。得到了以下结果：1.地基动力柔度是地基的一种与频率相关的动力特性，用近似有理函数表示，然后用与频率无关的弹簧和阻尼器组成的振动系统来代替。该方法使土-结构相互作用体系的地震反应分析成为可能。考虑圆柱形地下室埋设在与其外部土介质之间存在软化区的土地基中，讨论了竖井刚度对地基-地基体系振动特性的影响。指出软弱土层的波速越小，在较低的频率下，地下室顶部位移响应的实部越大。利用振动试验机对埋置基础进行了振动试验。本试验的一个特点是处理了两种情况，即基础与其外土地基之间有间隙，基础周围填满了地基。讨论了西德菲尔效应对幅度特性的影响。根据这些振动特性，计算了一个等效弹簧系数和一个粘性阻尼系数，特别是将这两个系数分为基础底部的贡献部分和地基侧边的贡献部分。结果表明，水平激励下，侧倾对等效弹簧和粘性阻尼系数的影响大于竖向激励，而粘性阻尼对等效弹簧和粘性阻尼系数的影响大于弹簧系数。

A purpose of this project is to evaluate quantitatively equivalent stiffness coefficient and viscous damping coefficient on a soil ground, analytically and experimentally. Following results are obtained.1. Dynamical ground compliance which is a dynamic property of a soil ground and which is dependent on frequency, is represented by an approximate rational function, and then is replaced by a vibration system which consists of springs and dashpots which are independent on frequency. This method makes the earth-quake response analysis of the soil-structure interaction system possible.2. Considering that a cylindrical basement is buried in a soil ground with a softer zone between it and it's outer soil medium, the effect of sidefill rigidity on vibration characteristics of a soil-basement system is discussed. It is pointed out that the smaller the wave velocity of the softer zone to that of the outer soil medium, the greater the real part of the displacement response at the top of the basement, in lower frequency.3. Vibration tests on embedded foundations are carried out by using of a vibration generator. A feature of this experiment is to treat with the two cases for the foundation having a gap between it and it's outer soil ground, and the foundation filled up around it. The effect of sidefill on the amplitude characteristics is discussed.4. From these vibration characteristics, an equivalent spring coefficient and a viscous damping coefficient are calculated, especially, both coefficients are separeted into a part of contribution at the bottom and a part of that at the side of the foundation. It is pointed out that the effect of sidefill on equivalent spring and viscous damping coefficients is greater for horizontal excitation than vertical one, and also is greater for viscous damping than spring coefficient.