复合地基黏性土路堤土拱效应分析

Soil arch effect analysis of cohesive soil embankment on composite foundation

现行规范中桩土应力比计算公式只适用于无黏性土路堤,工程实践中对桩帽复合地基与桩梁复合地基的选择也常发生争议。对桩帽复合地基、桩梁复合地基分别推导了适用于黏性土路堤的桩土应力比计算公式。分析表明,桩帽和连梁面积相同时,设置桩帽的路堤桩土应力比、桩荷载率均大于设置桩梁的路堤桩土应力比、桩荷载率。对于拱脚、拱顶均为无黏性土的桩帽复合地基路堤,路堤高度小时拱顶屈服,路堤高度大时拱脚屈服。拱顶屈服时,桩土应力比随路堤高度增大而增大;拱脚屈服时,桩土应力比不再随路堤高度增大而变化。对拱脚为无黏性土、拱顶为黏性土的桩帽复合地基路堤,路堤高度小时土拱不屈服,路堤高度较大时拱脚屈服,路堤高度大时拱顶屈服。土拱不屈服或拱脚屈服时,桩土应力比随路堤高度增大而增大;拱顶屈服时,桩土应力比随路堤高度增大而减小。对拱脚、拱顶均为黏性土的桩帽复合地基路堤,路堤高度小时土拱不屈服,路堤高度大时拱脚屈服。

The calculation formulas of pile-soil stress ratio in the current codes are only applicable to the non-cohesive soil embankment. In engineering practice, the choice of composite foundation with pile caps and composite foundation with beams is often controversial. For composite foundation with pile caps and composite foundation with beams, the formulas of pile-soil stress ratio suitable for cohesive soil embankment are deduced respectively. It is shown that the pile-soil stress ratio and pile load ratio of the embankment with pile caps are larger than those of the embankment with pile beams when the area of pile caps and connecting beams is the same. For the composite foundation embankment with pile caps with non-cohesive soil at arch foot and vault, the soil of the vault reaches the yield state when the embankment height is small, and the soil of the arch foot reaches the yield state when the embankment height is large. The pile-soil stress ratio increases with the increase of embankment height when the vault soil yields, while the pile-soil stress ratio has no larger changes with the increase of embankment height when the foot soil yields. For the composite foundation embankment with pile caps with non-cohesive soil at the arch foot and cohesive soil at the vault, the soil arch does not yield when the embankment height is small, the soil at the arch foot yields when the embankment height is large, and the soil at the vault yields when the embankment height is higher. The pile-soil stress ratio increases with the increase of embankment height when the soil arch does not yield or the soil at the arch foot yields and decreases with the increase of embankment height when the soil at the vault yields. For the composite foundation embankment with pile caps with cohesive soil at arch foot and vault, the soil arch does not yield when the embankment height is small, and the soil of the arch foot reaches the yield state when the embankment height is large.