长桩桩侧摩阻力分布与地基附加应力问题及对群桩沉降计算的影响

Distribution of shaft resistance of long piles and additional stress of foundation and their influences on settlement calculation of group piles

实测资料表明,工作荷载下传统Geddes解假设桩侧阻分布与长桩及超长桩实测侧阻分布差别较大,在工作荷载作用下长桩及超长桩桩身上部侧阻首先发挥。在对超长桩实测桩身侧阻分布的归纳总结基础上,建议了桩侧阻两段和三段线性分布模式,并通过对Geddes应力解的叠加,推导了两段和三段线性分布组合的侧阻分布模式下的地基附加应力解。建议侧阻分布模式与Geddes侧阻分布模式的对比分析表明,Geddes侧阻分布模式得到的桩端以下桩间土的竖向附加应力明显大于建议模式的结果,导致Geddes侧阻分布模式得到的群桩沉降比大于建议的侧阻分布模式计算的沉降比,Geddes侧阻分布模式夸大了群桩内部各桩的相互作用。实例计算表明,其它条件相同时,建议的侧阻分布模式计算得到的沉降与实测值更接近一些。

The measured data show that the distribution of shaft resistance of long and super long piles under vertical working load is quite different from the suggested one by Geddes＇ solution.The shaft resistance is first fully mobilized at the upper part of the long and super long piles under the working load.Based on the measured shaft resistance distribution of the long and super long piles,both the simplified bilinear and the trilinear patterns of the shaft resistance are suggested.The additional stress solutions of the bilinear and the trilinear distribution patterns are deduced by using the combination of Geddes＇ solution.The comparison between the solution of the proposed patterns and the Geddes＇ solution shows that the additional stress beneath the piles of the Geddes＇ solution is significantly greater than that of the proposed method.So the settlement ratio of Geddes＇ solution is greater than that of the proposed method and thus the Geddes＇ solution overestimates the interaction of group piles.Through the back analysis of case studies,it is found that the settlement predicted by the proposed method is closer to the measured one compared with that predicted by the Geddes＇ solution.