Study on a Method to Simulate a Soil-Pile Foundation System

本计画的目的是在分析与实验研究的基础上，提出一个合理的土-桩基础系统模型。作为试验研究，利用振动发生器进行了足尺钢桩和混凝土桩的振动试验，桩顶混凝土块由于垂直和水平谐波激励。得到以下结果.激振器的偏心力矩越大，土-桩基系统的共振频率越低.桩顶的固支状态（自由和固定）对桩土-桩基系统的刚度系数和粘滞阻尼系数均有影响.在竖向激励下，桩身轴向动应变存在于更深的区域，而在水平激励下，桩身轴向动应变在更深的区域消失。桩与周围土体之间的空隙似乎出现在地表附近.脉冲激励下桩基响应的傅立叶谱与振动台试验得到的幅值特性相似。从而为土-桩基系统的脉冲试验提供了依据。通过对桩-软土-土系统振动特性的分析研究，得出以下结论.软土区刚度越小，桩土相互作用系统的共振频率越低，桩周差距越深，共振振幅越大.对于各种桩型，都必须考虑桩周软土区刚度的降低和桩周空隙的存在。研究结果表明，桩-软土带-土-桩周带空隙体系是最佳的分析模型。

A purpose of this project is to propose a reasonable model of the soil-pile foundation system, based on the analytical and experimental studies. As the experimental studies, the vibration tests of full scale steel and concrete piles with a concrete block at their tops due to vertical and horizontal harmonic excitations have been conducted by making use of a vibration generator. Following results are obtained.1. The larger the eccentric moment of the vibration generator, the lower the resonance frequency of the soil-pile foundation system.2. The consentraite condition of the pile top, which is free or fixed, effects on the stiffness coefficient and viscous damping coefficient of the soil-pile foundation system.3. In the vertical excitation, dynamic axial strain of the pile exists even deeper region, but in the horizontal excitation, it vanishes at deeper region. And it seems that gap between the pile and its surrounding soil ground occurs in the vicinity of the ground surface.4. Fourier spectrum of response of pile foundation due to impulseexcitation is similar to its amplitude characteristics obtained from the vibration generator test. Then impulse test of the soil-pile foundation system is available. From the analytical study on vibration characteristics of the pile-softer zonesoil system, following results are followed.5. The lower the stiffness of the softer zone, the lower the resonance frequency of the soil-pile interacion system, and the deeper the gap around the pile, the greater the resonance amplitude.6. The reduction of the stiffness of softer zone and the existance of gap around the pile must be considerd for every kind of piles. As the result of their studies, ti is pointed out that the pile-softer zone-soil system with gap around the pile is the best analytical model.