软土地区基坑坑底隆起稳定破坏滑动半径研究

为了研究软土地区基坑坑底隆起的破坏模式并确定合理的隆起破坏滑动面大小,采用不连续布局优化法对不同围护结构插入比条件下的基坑坑底隆起失稳滑动面进行分析; 通过大量计算得到可用于判断滑动面是否通过围护结构底端的不同基坑开挖深度下土体强度和围护结构临界插入比的幂函数关系表达式; 通过分析围护结构插入比较小时归一化的坑底隆起破坏滑动半径和围护结构插入比的关系,得到修正传统圆弧滑动法滑动半径的对数表达式及其系数。最后,将修正滑动半径后计算的安全系数与数值模拟结果进行了对比,验证了滑动半径公式的可靠性。结果表明:在插入比较大(大于临界插入比)情况下,滑动面通过围护结构底端; 在插入比较小情况下,滑动面不通过围护结构底端,需对传统圆弧滑动法进行修正; 提出的修正方法可为软黏土层较厚的基坑坑底隆起稳定分析时滑动半径的选取提供参考,同时可以解决传统圆弧滑动法在插入比较小时安全系数变化不合理的问题。

Research on Sliding Radius of Basal Heave Failure of Excavation in Soft Soil Area

In order to study the failure mode of excavation basal heave in soft soil area and determine the reasonable basal heave sliding surface, the discontinuous layout optimization method was adopted to analyze the sliding surface of the excavation basal heave with different insertion ratios of the retaining structure. The power function expressions of the soil strength and the critical insertion ratio of the retaining structure at different excavation depths were obtained through a lot of calculations, which can judge whether the sliding surfaces pass through the end of the retaining structure. By analyzing the relationship between the normalized basal heave sliding radius of excavations and the insertion ratio of the retaining structure when the envelope was relatively small, the logarithmic expression and its coefficient table were obtained, which can modify the sliding radius of the traditional slip circle method. Finally, the safety factor calculated by modifying the sliding radius was compared with the numerical simulation results, which verified the reliability of the sliding radius formula. The results show that the sliding surface passes through the end of the retaining structure when the insertion ratio is larger(the insertion ratio of the retaining structure is larger than the critical insertion ratio). The sliding surface does not pass through the end of the retaining structure when the insertion ratio is relatively small, which needs to be improved. The proposed correction method can provide a reference for the selection of the sliding radius when analyzing the basal heave stability of excavations with thick soft clay. At the same time, it also solves the problem of changes irrationally in the safety factor of traditional slip circle method when the insertion ratio is small.