刚性桩复合地基桩顶埋入式垫层机理分析

Mechanism analysis of pile-top embedded cushion of rigid pile composite foundation

基于Meyerhof理论,提出了改进的桩顶埋入式垫层,推导出垫层极限桩土应力比的计算公式,并对桩顶埋入式垫层的作用机理进行了分析。研究发现:桩顶埋入式垫层可减少桩顶向上刺入量和地基沉降量,极限桩土应力比随刺入量的增加和垫层内摩擦角的增大而增大。提出了考虑桩顶垫层厚度及桩距影响的极限桩土应力比修正计算方法,推导了相应的计算公式和计算曲线,可供实际工程应用时查询。研究表明:修正后的埋入式垫层极限桩土应力比随桩顶预埋深度与垫层厚度之比的增加而增大,随桩距的增加而减小。通过算例分析,认为桩顶埋入式垫层具有垫层厚度和预埋深度可双向调节的优点,可用于调节复合地基应力和控制差异沉降,并可作为高层建筑地基变刚度调平设计的手段。

Based on the theory of Meyerhof,an improved form of composite foundation cushion,the pile-top embedded cushion was presented. The calculation formula of the ultimate pile-soil stress ratio of cushion was developed,and the work mechanism of pile-top embedded cushion was analyzed. It is found that the pile-top embedded cushion can reduce the piercing amount of pile and foundation settlement. The ultimate pile-soil stress ratio increases with increasing the piercing depth and internal friction angle. The modified calculation method of ultimate pile-soil stress ratio considering the influence of cushion thickness over pile top and pile spacing was proposed,and relevant calculation formula and calculation curves,which was available for inquiry in practical engineering,were deduced.The study results indicate that modified ultimate pile-soil stress ratio increases with increasing ratio of the piercing depth to the cushion thickness and decreases with increasing pile spacing. The calculation example analysis shows that pile-top embedded cushion has the advantage in bi-directional adjustment of cushion thickness and pre-embedded depth. The pile-top embedded cushion can be used to adjust the stress of composite foundation and control differential settlement,and can also serve as a means of variable rigidity of high-rise building foundation design.