砂土中扩底应力对深埋扩底抗拔桩承载力的影响

采用极限平衡法计算深埋扩底抗拔桩的承载力,需要确定破坏面的形状参数和应力条件。针对已有模型试验的研究结果,结合不同桩长扩底抗拔桩统一破坏模式,对上述问题进行了初步探讨。基于应力莫尔圆研究认为,仅考虑自重应力条件得到的破坏面法向应力明显小于扩底附近的实际破坏面应力条件,导致破坏面影响高度计算结果偏大。基于模型试验的试验结果,对扩底应力的增强系数进行了反算,该值在1.3到2.7之间,比被动土压力系数3.4要小,对扩底角度变化不敏感。只是初步的机理探讨,考虑到深埋扩底桩的埋深影响,该问题值得进一步深入研究。

Influences of stress around enlarged base to uplift capacity of deep belled piles in sand

It is necessary to determine the shape parameters of the failure surface and stress conditions of soil when the limit equilibrium method is adopted to calculate the bearing uplift capacity of a deep belled pile. Based on the published model test results, a preliminary discussion is given on the above problems with a unified failure mode for belled piles with short or long pile lengths. According to the concept of Mohr stress circle, if only the self-weight is considered, the normal stress of the failure surface is obviously less than the actual one around the enlarged base and leads to a larger influence height. Based on the model test results, the stress coefficient on the failure surface is back calculated, and it is found that the value of coefficient is in the range of 1.3 to 2.7, which is insensitive to the base angle. The effect of embedment depth on the stress coefficient is not considered, which needs further studies.