基坑悬臂排桩支护局部失效引发连续破坏机理研究

虽然已有很多基坑连续倒塌破坏的工程案例,局部破坏可能导致的连续垮塌规模和造成的后果也越来越大,但是由局部破坏发展为大规模连续破坏的机理还少有研究,也缺乏针对基坑连续破坏的控制方法和设计理论。以排桩支护的长条形基坑为例,采用显式有限差分法、离散元法及模型试验对局部支护结构失效情况下的基坑进行了模拟,对基坑土压力的重分布和支护结构受力的变化规律进行了分析和相互对比验证,初步揭示了连续破坏在基坑长度方向上的传递机理,提出了荷载传递系数的概念,即临近破坏第一根桩内力的提高倍数,并发现其是决定基坑是否发生连续破坏的重要因素。土体强度越高,荷载传递系数越高。在局部破坏发生之后很短时间内,未破坏部位土压力和结构受力迅速升高达到最大值。排桩顶设置的连续冠梁可以降低传递系数,对提高基坑支护结构抗连续破坏能力有重要作用。

Mechanism of progressive collapse induced by partial failure of cantilever contiguous retaining piles

Although there are many progressive collapse cases of deep excavations and the scale of progressive collapse caused by the initial partial failure of the retaining structures and its consequences are becoming larger and larger, the researches on the mechanism how the partial failure evolves to large-scale progressive collapse are still limited, and the control methods and design theories of progressive collapse haven't been developed. In this study, the long strip excavation with cantilever contiguous retaining piles under partial failure is simulated by the explicit finite difference method, discrete element method and model tests. The redistribution of soil pressures and change of internal forces of the retaining structures are analyzed and compared using the simulated results, and then the transfer mechanism of progressive collapse in the longitudinal direction of the excavation is preliminarily revealed. The concept of load transfer coefficient is raised, which equals to the increment ratio of the internal force of the piles adjacent to the partial failure, and it is found that the load transfer coefficient is a crucial factor which can determine whether or not the progressive collapse can happen. For a retaining structure, the higher the soil strength is, the larger the load transfer coefficient is. When partial failure occurs, soil pressures and internal forces of adjacent intact retaining structures increase rapidly. The continuous top-beam installed on the top of piles can lower the load transfer coefficient, and plays an important role in increasing the capacity of retaining structures to resist progressive collapse.