多元复合地基中柔性桩-土-垫层的相互作用

采用柔性桩与桩周土的相对位移表达式来表示多元复合地基中柔性桩桩侧摩阻力的分布规律，结合变形协调条件、物理方程和力的平衡方程，分析了刚性承台下柔性桩-土-垫层的相互作用，并将计算结果与模型试验结果进行了对比。结果表明：增加垫层厚度或提高垫层变形模量均能缓解桩顶应力集中，充分调动桩周土的承载能力；随着柔性桩的刚度提高，或垫层厚度增大，或垫层变形模量提高，柔性桩复合体的承载力均有不同程度的提高；最大桩侧摩阻力位于桩顶以下1／4～1／3桩长处；由于桩顶向垫层刺入使桩身存在负摩擦区，导致桩身最大轴力并不在桩顶，又因柔性桩的刚度不大，桩顶刺入作用较弱，负摩擦区段的长度短，故负摩擦不大。对比试验结果验证了所提出的方法具有可行性，对复合地基的设计计算具有指导意义。

Interaction of Flexible Plie-soil-cushion in Multi-element Composite Foundation

Based on flexible pile side friction in the multi-element composite foundation, the distribution regularity was expressed by the relative displacement between flexible pile and surrounding soil. By combining deformation harmonious condition, physics equation and equilibrium equation of force, interaction of flexible pile-soil-cushion were analyzed under rigidity pile cap, results of model tests were compared with those of calculation. Results indicate that stress concentration of pile top can he abated by cushion incrassation or cushion modulus increase; bearing capacity of composite body for flexible pile can be mobilized richly. Meanwhile, bearing capacity of composite body for flexible pile has different degrees increase by increasing rigidity of flexible pile, or enhancing cushion thickness or modulus. Maximal pile side friction lies on 1/4 to 1/3 piles below pile top. Because there is negative friction area in pile owing to pile top sticks into cushion, maximal axial force in pile does not lie on pile top, as rigidity of flexible pile is not very big, sticking action of pile top is faintish, length of negative friction area is very short, and negative friction is very small. The comparison indicates that the proposed method is feasible and has significant guidance for the composite foundation design.