STUDY ON QUANTITATIVE EVALUATION OF SOIL GROUND DAMPING

本计画的目的是以解析与实验的方法，来定量评估地基的等效刚度系数与黏滞阻尼系数。得到以下结果.地基动力柔度是地基的一种动力特性，它与频率有关，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.考虑地下室与地基之间存在软土区的情况，讨论了边墙刚度对地基-地下室系统振动特性的影响。指出软土区的波速相对于外层土介质的波速越小，在低频时，基底顶部位移响应的真实的部分越大.利用振动发生器对埋置基础进行了振动试验。本实验的一个特点是分别处理了基础与地基之间有间隙和周围有填土的两种情况，讨论了侧填对振幅特性的影响.根据这些振动特性，计算了等效弹簧系数和粘滞阻尼系数，特别是将这两个系数分解为底部贡献和侧部贡献两部分。指出侧填对等效弹簧系数和粘性阻尼系数的影响在水平激励下大于垂直激励，对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.