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

本课题的目的是在分析和试验研究的基础上，提出一种合理的土-桩基础体系模型。作为试验研究，利用振动台对顶端带有混凝土块的足尺钢桩和混凝土桩在竖向和水平简谐激励下的振动进行了试验研究。得到了以下结果：1.振动器的偏心弯矩越大，桩-土基础体系的共振频率越低。桩顶自由或固定条件对土-桩基础体系的刚度系数和粘性阻尼系数的影响。在竖向激励下，桩的动轴向应变存在更深的区域，而在水平激励下，动轴向应变在更深的区域内消失。桩与周围土层之间的缝隙似乎发生在地表附近。桩基在脉冲激励下的响应傅里叶谱与振动台试验所得的幅值特性相似。在此基础上，进行了土桩基础体系的冲击试验。通过对桩基-软弱夹层体系振动特性的分析研究，得出以下结论。软化区的刚度越小，桩-土相互作用体系的共振频率越低，桩周间隙越大，共振幅度越大。对于每种桩型，都必须考虑软化区刚度的降低和桩周间隙的存在。研究结果表明，桩周有间隙的桩-软化带-土体系是最好的分析模型。

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.