单排弹性空心管桩屏障对平面P波的隔离

由于桩体的长度远大于直径，因此将单排弹性空心管桩构成的非连续屏障对平面P波的隔离问题简化成二维平面问题，采用波函数展开法和Graf加法定理，根据桩-土界面处完全联结和管桩内壁完全自由的边界条件，得到了问题的理论解。引入无量纲位移和透射系数等概念，通过数值计算，分析了弹性空心管桩的壁厚、桩土模量比、管桩间距和管桩数量对屏障对平面P波隔离效果的影响，结果表明：隔离效果随着管桩壁厚和桩间距的减小而提高；隔离效果随着桩土模量比的增大而提高，但当桩土模量比大于500后，隔离效果提高不明显，此时可等价为刚性屏障；随着管桩数量的增多，最佳隔离区域在增大，最佳隔离位置在前移。为非连续屏障的隔振设计提供了理论依据。

ISOLATION OF PLANE P WAVES BY DISCONTINUOUS BARRIERS COMPOSED OF A ROW OF ELASTIC HOLLOW PIPE PILES

The ratio of length to diameter of a pile is so large that the vibration isolation of incident plane P waves by discontinuous barriers composed of a row of elastic hollow pipe piles can be simplified as a two-dimensional plane problem.The stresses and displacements at the interfaces between piles and soils are considered as continuous,while the inner walls of piles are assumed stress free.The theoretical solutions for vibration isolation are obtained through the expansion method of wave functions and the Graf's addition theorem.The effects of pile thickness,modulus ratio of pile to soil,span between piles and sum number of piles on vibration isolation are studied in detail.A few important conclusions are drawn out from analysis,and they are:(1) the isolation effects increase with decrease in pile thickness and pile span,(2) the isolation effects increase with increase in the modulus ratio of piles to soils in the initial stage,and then,gradually approach constant after the ratio exceeds 500,which illustrates the piles can be regarded as rigid at that time,(3) as the sum number of piles increase,the best isolation areas increase and the position with best isolation effects moves forward,which provide theoretical basis for the design on discontinuous barrier for vibration isolation.