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超长桩基础作为一种承载性能较好的基础形式,已经越来越多地被工程界所运用,但其内在的受力特性仍然不是十分明确。通过单桩与群桩模型试验研究了超长桩在竖向荷载作用下的受力沉降关系,得出其沉降量主要是由桩体压缩提供。由计算所得压缩量,求出试验条件下的桩身压缩系数,与某现场试验数据对比,发现相差较大,推测其原因。由轴力分布图,验证了超长桩的受力特性,并由此提出了确定有效桩长的必要性。观察到侧摩阻力呈现“驼峰形”分布,随着荷载增加逐渐向桩端发展;下部桩体的临界桩土位移比上部桩体要小,但其最大侧摩阻力要比上部桩体大,故在推导超长桩承载力公式时,对于不同桩段要分别乘上不同软化系数综合考虑。
As a basic form with good bearing performance, the ultra-long pile foundation has been increasingly used by the engineering community, but its inherent stress characteristics are still not very clear. Based on the single-pile and group-pile model tests, the relationship between force and settlement of super-long pile under vertical load is studied, and it is concluded that the settlement is mainly provided by compression of the pile. From the calculated compression amount, the compression coefficient of the pile under the test conditions was calculated, and compared with a field test data, it was found that there was a large difference and the reason was inferred. From the axial force distribution chart, the force characteristics of the ultra-long pile were verified, and the necessity of determining the effective pile length was proposed. Observed that the lateral friction resistance presents a “hump-shaped” distribution, which gradually develops toward the pile end as the load increases; the critical pile-soil displacement of the lower pile is smaller than that of the upper pile, but the maximum side friction resistance is higher than that of the upper pile. Therefore, when deriving the formula for the bearing capacity of ultra-long piles, comprehensive consideration should be given to the different softening factors for different pile sections.