下部扩大段复合桩抗拔承载力设计方法与试验研究

下部扩大段复合桩是一种新型抗拔桩，采用理论分析与现场试验相结合的方法，分析了下部扩大段复合桩抗拔作用机制，提出了该桩型单桩抗拔承载力理论模型及计算参数。结果表明：在一定上覆土层厚度条件下，下部扩大段桩侧阻力受到上端阻力作用的影响得到增强，试验条件下采用经验参数法进行计算时的发挥系数可达1.6；上部非扩大段抗拔承载力受到扩大段上端阻力的影响得到减弱，发挥度有所降低；上部非扩大段桩径相对扩大段较小时，仅可考虑扩大段桩侧阻力和上端阻力进行下部扩大复合桩抗拔承载力计算；通过与试验对比，验证了模型和理论方法的可靠性、实用性。该研究成果可供工程设计参考。

Design method and experimental study of uplift bearing capacity of the lower enlarged composite pile

The lower enlarged composite pile is a newly developed uplift pile. The uplift mechanism of the lower enlarged composite pile is analyzed by combining theoretical analysis and field experiments. Based on this, the theoretical model and calculation parameters of uplift bearing capacity of the single pile for this pile type are proposed. The results show that the lateral resistance of the lower enlarged pile is enhanced by the effect of the upper resistance under a certain thickness of overlying soil layer. The mobilization factor can be 1.6 when calculated by empirical parameter method under testing conditions. The uplift bearing capacity of the upper non-enlarged composite pile is weakened by the influence of the upper resistance of the enlarged section, and the mobilization is decreased. When the pile diameter of the upper non-enlarged section is smaller than that of the enlarged section, the uplift bearing capacity of the lower enlarged composite pile is calculated by considering only the lateral resistance of the enlarged section and the upper resistance. The reliability and practicability of the model and theoretical method are verified through comparison with experimental results. The research results can be used as a reference for engineering design.