单桩承载力对刚性桩复合地基路堤稳定性的影响

现行规范中刚性桩复合地基路堤稳定分析方法不能反映单桩承载力、桩帽等对路堤稳定性的影响,计算的路堤稳定安全系数严重偏大,导致部分刚性桩复合地基路堤滑塌。为克服刚性桩复合地基路堤现有稳定分析方法的缺陷,在研究刚性桩复合地基路堤滑塌原因的基础上,分析了路堤滑塌时桩土相互作用,及刚性桩提高路堤稳定性的机理。然后,在分析刚性桩复合地基路堤现有稳定分析方法的缺陷的基础上,将修正密度法完善为修正重度法。最后,为研究单桩承载力对刚性桩复合地基路堤稳定性的影响,利用修正重度法分析了刚性桩长度、间距、扩底、桩帽等对路堤稳定性的影响,对比了不同稳定分析方法计算结果,并对刚性桩复合地基路堤设计提出了建议。研究表明：单桩承载力对密桩复合地基路堤稳定性影响很小,对疏桩复合地基路堤稳定性影响很大;增大单桩承载力比减小桩间距更合理;刚性桩在持力层中扩底比加大桩长更有效;利用桩帽、土拱等措施将大部分路堤荷载转移到桩顶方可发挥单桩承载力对路堤稳定性的作用;软土强度随深度增大不明显时应慎用悬浮桩复合地基。刚性桩复合地基路堤宜采用“强桩大帽”的疏桩复合地基方案。

Influences of bearing capacity of piles on stability of embankment with rigid pile composite foundation

The influences of bearing capacity and cap of rigid piles on the stability of embankment with rigid pile composite foundation cannot be taken into account in the methods recommended by the existing Chinese codes. Some embankments with rigid pile composite pile foundation slid owing to that the factor of safety gotten by those methods is much larger than the real value. To avoid the defects of the existing methods, the interactions between the piles and the soil among piles during sliding are analyzed, and the mechanism of improving the embankment stability by rigid piles is analyzed by analyzing the causes of slides. Then the revised density method is improved to be the revised weight method by analyzing the defects of the existing stability methods. Finally, the influences of the length, distance, enlarged base and cap of rigid piles on the embankment stability are studied by use of the revised weight method, and the influences of their bearing capacity on embankment stability are evaluated. The analysis results of different methods are compared. Some design proposals for the embankment with rigid pile composite foundation are put forward. It is shown that the influences of bearing capacity of piles on the stability of embankment with dense pile composite foundation are little but great on the embankment with sparse pile composite foundation. Increasing the bearing capacity of piles is more reasonable than decreasing the distance of piles. The belled piles are more efficient than those increasing their length. The rigid piles with large bearing capacity can play an important role to increase the stability of embankment only if most loads of embankment are transferred to the piles by pile caps and soil arch. The hanging piles should not be used if the strength of soft clay increases little along depth. The rigid pile composite foundation under embankment should be designed as the sparse pile composite foundation with large bearing capacity and pile cap.