深厚软土地区倾斜桩组合支护基坑稳定性研究

Research on Stability of Foundation Pit With Inclined Pile Combination Support in Deep Soft Soil Area

倾斜桩组合支护是一种新型基坑支护形式,适用于大面积无内支撑的基坑。本文依托天津市某倾斜桩支护基坑项目,设计6种预制桩支护对比结构,其中4种为倾斜桩组合支护,进行基坑开挖大型现场试验,量测分析周边不同环境下各组合结构支护基坑的变形情况,并运用Plaxis 3D有限元软件进行基坑安全性分析。结果表明:不同形式的倾斜桩组合支护中,内斜直组合桩身位移最小,支护效果最优;基坑周边存在超挖等不利因素时,倾斜桩组合支护的刚架效应、斜撑效应与重力效应决定其依旧能较好地发挥自身稳定作用;软土蠕变对斜桩基坑支护影响亦不容忽视,开挖至坑底时,应及时施工垫层和底板;数值模拟分析发现倾斜桩组合支护基坑安全系数及临界破坏形态受超挖影响小于常规排桩支护,小幅超挖对基坑的稳定性影响较低。

Inclined pile combined support is a new type of foundation pit support,which is suitable for large area foundation pit without internal support.In this paper,based on a sloping piles supporting of foundation pit project of Tianjin,the design of 6 kinds of precast pile supporting structure,including four kinds of combination of inclined pile supporting,to carry on the excavation of large field test,measurement analysis under different environment surrounding the combination structure supporting the deflection of the foundation pit,and the finite element software Plaxis 3D analysis of the stability of foundation pit.The results show that among the different types of inclined pile combination support,the inner inclined straight combination pile displacement is the least and the supporting effect is the best.When there are adverse factors around the foundation pit,such as over-digging,it is obviously different from the conventional pile row.The rigid frame effect,the diagonal brace effect and the gravity effect of the inclined pile combination support determine that it can still play a good role of its own stability.And the influence of soft soil creep on inclined pile foundation pit support should not be ignored,when the excavation reaches the bottom of the pit,cushion and floor should be constructed in time.Numerical simulation analysis shows that the influence of over-excavation on the safety factor and critical failure mode of foundation pit for inclined pile combination bracing is less than that for conventional pile row bracing,and small over-excavation has little influence on the stability of foundation pit.