红层软岩钢管微型桩抗压承载特性试验

为揭示红层软岩钢管微型桩抗压承载特性，为红层软岩地基加固设计提供参考，选取湖南衡阳强风化粉砂质红层软岩地基，开展了不同长度注浆钢管微型桩原位抗压静载试验，分析了桩体沉降、桩身轴力和桩侧摩阻力的分布规律，并与规范计算值进行了比较。在修正微型桩荷载传递函数的基础上，提出了考虑桩顶位移的微型桩抗压承载力预测方法，并通过原位试验结果进行了验证。研究结果表明：钢管微型桩轴力主要分布在桩身中上部，桩侧摩阻力沿桩身呈“三角形”分布；随桩长的增加，抗压承载力非线性增加，桩顶沉降量非线性减小；桩长越短，极限侧摩阻力峰值越大；相较于规范计算值，实测桩端阻力、全桩长范围极限摩阻力均值以及抗压承载力均偏小。采用该方法得到的抗压承载力预测值与原位实测值之间相关性较好，相对误差为0.6%~11.6%。对红层软岩地基进行钢管微型桩加固设计时，建议桩端阻力不计入抗压承载力，按纯摩擦桩进行设计，并对规范中的极限侧摩阻力推荐值折减。

Experimental Study on Compressive Bearing Characteristics of Micro-steel-pipe Piles in Red-bed Soft Rock

To reveal the compressive bearing characteristics of micro-steel-pipe piles in red-bed soft rock and provide reference for the reinforcement design of red-bed soft rock foundations, an in-situ compressive static test was carried out on grouting micro-steel-pipe piles of different lengths in the strongly weathered silty red-bed soft rock foundation in Hengyang, Hunan Province. The distribution of settlement, axial force, and friction resistance of the piles was analyzed and compared with the calculated results according to specification. Based on the modified load transfer function of micro piles, a prediction method for the compressive bearing capacity of micro-piles considering the displacement at the pile top was proposed and verified based on the experimental results of in-situ tests. The results show that the axial force of a micro-steel pipe pile is mainly distributed in the middle and upper parts of the pile, and the distribution of lateral resistance of micro-steel pipe piles along the pile body shows a triangle-shaped distribution. With an increase in pile length, the compressive bearing capacity increased nonlinearly, whereas the settlement at the pile top reduced. The shorter the pile length, the greater the value of the ultimate lateral resistance. Compared to the calculated results according to specification, the measured end resistance of the pile, the average measured value of the ultimate friction resistance of the pile in the range of its length, and the measured compressive bearing capacity would all be overestimated. The estimated compressive bearing capacity using the proposed prediction method shows a good correlation with the measured values with the relative error ranging from 0.6% to 11.6%. When reinforcing a red-bed soft rock foundation with micro-steel-pipe piles, it is suggested that the pile end resistance should not be included in the compressive bearing capacity, the design should be based on pure friction piles, and the recommended value of ultimate side friction in the specification should be reduced.