基坑抗隆起稳定性研究新进展

坑底隆起易造成基坑坍塌及邻近建(构)筑物不均匀沉降，是影响基坑安全的关键因素之一。针对近10年国内外基坑抗隆起稳定性研究进展，阐释了基坑宽度、土体各向异性及支挡结构嵌固深度等因素对坑底抗隆起稳定性影响规律，列举了近年来基于地基承载力模式及圆弧滑动模式的基坑抗隆起安全系数改进公式，对比了不同改进公式对应的破坏机制及适用范围。进一步介绍了可靠度分析方法在坑底隆起失效概率计算中的运用及失效概率影响因素。最后总结了圆形基坑及坑中坑式基坑坑底隆起破坏机制及抗隆起安全系数计算方法。得到以下结论:(1)基坑越窄、土体各向异性比越低及支挡结构嵌固段越深对基坑坑底抗隆起稳定性越有利，但当支挡结构位于均质土层且端部未嵌入较硬土层时无法体现此规律；(2)基坑坑底隆起的失效概率与岩土体材料及土体参数的空间变异性有关，与安全系数无直接联系；(3)由于尚未建立统一的计算模型，且如何考虑三维效应及拱效应也未明确，圆形基坑抗隆起稳定性分析至今未有统一定论；坑中坑式基坑内外坑间距决定抗隆起破坏机制，抗隆起安全系数应根据内部型及外部型两种不同破坏机制分别计算。

New Progress in Research on Basal Heave Stability of Foundation Pit

Basal heave is easy to cause foundation pit collapse and uneven settlement of adjacent buildings (structures), which is one of the key factors affecting the safety of foundation pit.According to the research progress of basal heave stability of foundation pit at home and abroad in recent 10 years, the influence rules of the factors such as the width of foundation pit, soil anisotropy and embedment depth of retaining structure on basal heave stability of foundation pit is explained. The improved formula of basal heave safety factor of foundation pit based on foundation bearing capacity mode and circular sliding mode in recent years is listed. The failure mechanism and application scope of different modified formulas are compared. Furthermore, the application of reliability analysis method to the calculation of failure probability of basal heave and the influencing factors of failure probability are introduced. Finally, the failure mechanism of the basal heave of circular foundation pit and pit in pit type foundation pit and the calculation method of the safety factor are summarized. The results are as follows: (1) The narrower the foundation pit; the lower the anisotropy ratio of soil; the deeper the embedded depth of retaining structure, the more stable the basal heave of the foundation pit. But there is no such rule when the continuous wall is located in homogeneous soil and does not enter into the harder soil layer. (2) The failure probability of basal heave is related to the spatial variability of soil materials and soil parameters, but not directly related to the safety factor. (3) Because the unified calculation model has not been established, and how to consider the three-dimensional effect and arch effect is not clear, there is no unified conclusion on the basal heave stability analysis of circular foundation pit; The distance between the inner and outer pits of pit in pit foundation pit determines the basal heave failure mechanism, and the basal heave safety factor shall be calculated respectively according to the two different failure mechanisms of internal type and external type.