逆作复合桩基承载性能试验研究

Experimental research on load-carrying properties of composite foundation in top-down order

逆作复合桩基作为一种新型的基础形式,对其承载性状、工作机理的研究很有必要。通过设计单桩、带台单桩及带台两桩系列试验,对极限荷载下逆作复合桩基的荷载与沉降关系、桩土荷载分担特性以及桩体受力性能进行了研究。结果表明:采用逆作复合桩基,先进行基础底板和部分上部结构的施工,而后继续进行上部结构、钢管桩压桩以及封桩施工能充分利用土体的承载能力,压桩前土体与基础底板保持严密接触,上部结构荷载全部由地基土承担;压桩后,使土体的刚度得到了改善了,沉降减小,承载力提高;封桩后,继续增加的荷载主要由桩体承担,直至桩达到极限承载能力,封桩时机的选择决定着桩土荷载分担的比例及基础沉降特性;由于承台的影响,使桩身上部轴力衰减平缓,桩侧摩阻力被削弱,同时使桩身中下部轴力衰减加剧,侧摩阻力发挥得到增强。

The complex foundation by top-down method is a new kind of foundation.It is necessary to study its bearing mechanics and working behaviors.The model tests on a single pile and a series of single-pile and two-pile foundations are designed to investigate the relation between bearing capacity and settlement,the load sharing ratio between soil and pile as well as the load carrying properties of complex foundation by top-down method.The results indicate that the complex foundation in top-down order,which first constructs foundation plate and a part of superstructure and then presses steel piles and seals the piles subsequently,can take full advantage of soil bearing capacity.The foundation plate tightly keeps contact with foundation soil which bears all the loads of superstructure before pressing piles;the rigidity of soil is strengthened after pressing pile,the settlement of foundation decreases and the bearing capacity is enhanced.The most of incremental loads are supported by pile until the pile reaches the ultimate bearing capacity,and the timing of sealing pile is responsible for load sharing between pile and soil and the behavior of foundation settlement.The pile cap makes distribution of axial force gently and frictional resistance decrease at the upper part of pile,meanwhile,frictional resistance at the rest part increases.