上海软土地区打入桩基长期沉降性状研究

通过对上海25栋高层建筑打入桩基长期沉降观测资料的对比分析,研究压缩层的组成与桩周土特性对打入桩基长期沉降性状的影响,指出桩周浅部厚砂土层对打入桩基长期沉降性状的影响同压缩层有密切的关系。当压缩层以准砂土为主（准砂土比β〉75%）时,桩周厚砂土层对降低桩基沉降及改善沉降性状有明显作用;当准砂土比β〈50%（或可塑性黏土比β3〉50%）时,桩周厚砂土层的上述作用将消失。即使在桩周存在厚砂土层时,压缩层组成对桩基沉降性状的基本特征起主导作用仍然是具有普遍意义的概念。在浅部厚砂土层中得到的上述研究结果,实际上同挤土桩施工的复杂作用有关。

Study on long-term settlement behavior of driven pile foundation in Shanghai soft soil area

Based on the comparison of the long-term settlement measurement data of driven pile foundation of twenty-five high rise buildings, the effects of composite of pile toe compressible layer and soil property surrounding the pile shaft on long-term settlement characteristics of driven pile foundation are studied and the results show the effects on settlement behaviors of driven pile foundation induced by thick sand layer existing in the shallow of pile shaft are very relevant to the compressive soil layers underlying the pile tip. The function of thick sand layer of pile shaft to decrease the pile foundation settlements and improve the settlement behaviors is remarkable when the compressive soil layers are mainly composed by quasi-sand layers; namely the quasi-sand ratio β more than 75 percent whereas the function is disappeared when the quasi-sand ratio β is less than 50 percent. The concept of component of compressive layers mainly functioned on the pile foundation settlement behaviors is ordinary existed in the case of the existed of thick sand layer surrounding the pile shaft. The results above mentioned are strictly related to the complex construction action induced by the construction of displacement pile.