考虑土体强度不均匀性时宽窄基坑坑底隆起稳定研究

在基坑坑底隆起稳定性分析中,准确的破坏模式及滑动面是确定安全系数的基础。然而,基坑坑底隆起破坏模式种类繁多且形式各异。传统的经典基坑坑底隆起稳定分析以及规范分析方法在破坏模式及滑动面的选取上均存在差异和局限性。基于不连续布局优化法,首先研究了土体强度不均匀性对不同宽度基坑坑底隆起稳定性的影响。结果表明,软土层厚度较大且土体强度沿深度逐渐增长时,宽基坑坑底隆起滑动面并不覆盖整个坑底,即相当于软土层下部存在一硬土层,限制了滑动面向下延伸。进一步,分析了围护结构长度及抗弯强度对破坏模式及安全系数的影响,并提出以滑动面触碰围护结构来区分宽窄基坑。在宽基坑中,当围护结构嵌固深度较小时,失稳破坏滑动面并不通过桩底,此时应用绕最下道支撑的圆弧滑动模式时应适当修正滑动面半径。对于窄基坑,应用圆弧滑动模式时需修正坑内滑动面,以考虑窄基坑的空间效应对安全系数的提高作用。

Basal heave stability of wide and narrow excavations considering non-homogeneous features of soft clay

In the analysis of the basal heave stability of excavations, the reasonable failure mode and the slip surface are the basis for determining the safety factor. However, there are many different types of basal heave failures. The traditional stability analysis methods and the existing codes have differences and limitations in terms of the failure mode and slip surface. Based on the discontinuity layout optimization method (DLO), the influences of non-homogeneous soil strength and excavation width on the basal heave failure mode are investigated. The results show that the soil inhomogeneity should be considered in the basal heave stability analysis. Furthermore, the influences of the length and bending strength of the retaining piles on the slip surface are analyzed, and the method to distinguish the wide and narrow excavations is proposed. For the wide excavations, when the retaining structures are short, the slip surface is below the toe of the retaining structures, and the slip surface should be adjusted when the circular slip method is used. For the narrow excavations, the slip surface should also be modified to consider that the space effect is benefit for the basal heave stability.