基坑坑底稳定性的机会约束评估方法

采用极限平衡理论对基坑坑底稳定性进行分析的方法是根据“确定性”的土体性质、滑动方式计算其抗隆起稳定系数，将运动单元法理论应用于极限平衡理论，并考虑强度折减原理，建立了适应不同类型滑裂面形式的坑底稳定性分析的“确定性”模型，在此基础上，考虑到坑底土力学性能的随机性及其强度参数不能满足约束条件的随机性，建立了机会约束的可靠性分析方法。针对圆弧滑动面和普-瑞法滑裂面进行计算比较，分析了不同滑动面圆心位置、坑底荷载、支撑荷载对支护结构插入比的影响，以及随机约束函数的置信水平对插入比的控制作用。以一工程实例实现了上述分析思想与方法。

Assessment methods of chance constrained on bottom stability of foundation pit

The limit equilibrium theory is used for analysis of heave resistant stability factor of foundation pit, which becomes dependent upon ‘deterministic’ properties of soil and slide surface. Considering the strength reduction principles and movement unit law which is used to limit equilibrium theory, a ‘deterministic’ analysis model of heave resistant stability factor of foundation which is adapted to different types of slide surfaces is established. Based on the ‘deterministic’ analysis model, reliability analysis of chance constrained programming is established in light of the randomness of the calculating parameters and the constraint condition; there may be no satisfactory strength parameters in the latter one. The calculation and comparison are carried out in view of circular sliding surface and Prandtl’ sliding surface. The influence factor of inserting ratio of deep braced excavation is analyzed for different circle centres, load on excavating pit bottom and bracing load on retaining structure. And also the control of random constraint function for the inserting ratio is studied. As an example, the analysis in light of the theoretical idea is taken out in some engineerings.