排桩支护体系的三维土拱效应及桩间距研究

Research on 3D Soil Arching Effect of Pile Wall Retaining System and Their Appropriate Spacing

为研究排桩支护体系中的土拱效应的三维分布、体系的安全性及合理桩间距的计算方法,利用三维有限元程序PLAXIS 3D对排桩支护体系、施工开挖、堆载等过程进行模拟,分析了不同阶段土拱效应的分布情况及不同阶段的安全性。并根据土拱的三维分布特性改进了已有的桩间距计算方法。计算显示开挖过程中桩间土拱前塌落区与摩尔库伦塑性区基本重合,在基坑1/2~2/3深度处土拱效应最为明显、塌落区最大,建议用已有公式计算这一段对应的合理桩间距,用于工程设计。有限元计算显示,本文中建议的方法所计算的桩间距能保证支护的安全性符合要求。

In order to reveal the 3D distribution of soil arching effect,the safety of pile wall retaining system and the method of determining proper pile spacing,the three-dimensional FEM software PLAXIS 3D was adopted to simulate the excavating processes to analyze soil arching effect and safety in different stages. Based on the distribution regularity of 3D soil arching effect,proper pile spacing was discussed. The results show that,safety factor of supporting system decreases gradually in the process of excavation,but the top load may improve the safety factor,which was a common phenomenon in pile anchor bracing system. It was also found that the arching effect was strengthened and then weakened along the depth. Furthermore,calculations showed that the potential sliding volume matched Mohr-Columb plastic zones well,with the largest size between the 1/2-2/3 depth. Finally,according to the3 D distribution characteristics of soil arch found,previous methods were improved and a modified method to calculate spacing of piles was put forward. It was suggested that pile spacing calculation should consider the safety of the depth range from 1/2 to 1/3 instead of the root,which would lead to overly conservative results. The safety of the method on pile spacing proposed in this paper was supported by subsequent FEM calculations.