筏板与桩基础的竖向动力相互作用

Dynamic interaction of axial vibration between pile groups and raft foundations

本文考虑了土的成层性和沿深度有变化的特性,将土层沿深度离散形成一系列均质的土层,各土层视为满足平面应变假定,应用传递矩阵法推导出单桩的动力阻抗;借助推求的桩-桩动力相互作用因子,来考虑群桩的桩-桩动力相互作用影响;通常研究承台板与群桩的竖向动力相互作用时假设承台板是刚性的,本文充分考虑了承台板具有一定的刚度、可以变形的柔性特征;并提出承台板-群桩动力相互作用模型,然后推得其动力相互作用方程。通过算例说明了承台板的刚度对承台板的动力作用是有影响的。研究表明,振动频率越低,柔性承台板的振幅与刚性承台板的振幅相差越大;随着频率的增大,两者差别也减小,并逐渐趋于相等。在承台板发生共振时,桩的反力出现明显的峰值,而且柔性承台板比刚形承台板的峰值大得多。

In consideration of the behavior of soil layer-forming and the characteristics of variation of soil along its depth, the pile group and surrounding soil are divided into a series of horizontal and homogeneous soil layers, and each layer is taken as to meet the planar strain assumption. The dynamic impedance of a single pile is developed by means of the transfer matrix method, and with the help of deriving pile-to-pile dynamic interaction factors to consider the effect of pile-to-pile dynamic interaction of pile group. In studying the dynamic interaction of axial vibration between pile cap and pile group, the pile cape is usually assumed to be extremely rigid. This paper presents a raft foundation-pile group dynamic model with its dynamic interaction equations deduced, in which the peculiarity of raft foundation that though it is a rigid body, yet it has the capability of flexibility, has been taken into account. Numerical example indicates that raft stiffness has significant effect on the dynamic interaction. Research shows the lower the vibrational frequency, the larger the difference of vertical amplitudes between flexible and rigid pile caps; while the higher the vibrational frequency, the smaller the difference, or even equal. The peak values of pile reactions will occur during pile cap resonance, in that case the peak values of flexible pile cap are much larger than those of the rigid ones.