The paper aims to analyse the influence of slenderness on the ultimate behaviour of piles with a very small diameter (less than 10 cm) that are often employed in soil reinforcement and for which the slenderness can significatively influence the failure behaviour, reducing the ultimate load. The aim is reached by means of numerical analyses on small-diameter piles of different geometries, embedded in clayey soil. The critical load is evaluated numerically in undrained conditions and then compared to the bearing capacity estimated by the classical approaches based on limit equilibrium method. The numerical model is first calibrated on the basis of the results of experimental laboratory tests on bored piles of a small diameter in a cohesive soft soil (average undrained shear strength cu = 15 kPa). The comparison between the critical load and the bearing capacity shows that their ratio becomes less than 1 for critical slenderness LCR that decreases, nonlinearly, with the decreasing of the pile diameter. The results of the analysis show that varying the diameter of the pile from 0.06 to 0.18 m, LCR varies from 65 to 200. The aforementioned evidence suggests that the evaluation of the ultimate load of piles of very small diameter has to follow the considerations on the critical load of the pile, especially if it is embedded in soft soil; on the contrary for piles of greater diameters (bigger than 20 cm) the buckling is not meaningful because LCR is so big that the common slenderness does not exceed it.

中文翻译：

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非常细长桩的行为分析：关注极限载荷

本文旨在分析细长对通常用于土壤加固的非常小直径（小于 10 厘米）桩的极限性能的影响，对于这些桩，细长可以显着影响破坏行为，从而降低极限荷载。目的是通过对嵌入粘土中的不同几何形状的小直径桩进行数值分析来实现的。在不排水条件下对临界载荷进行数值评估，然后与基于极限平衡法的经典方法估计的承载能力进行比较。该数值模型首先根据对粘性软土中小直径钻孔桩（平均不排水剪切强度 cu = 15 kPa）的实验室测试结果进行校准。临界载荷和承载力之间的比较表明，对于临界细长 LCR，它们的比率小于 1，随着桩径的减小呈非线性减小。分析结果表明，桩径从 0.06 m 到 0.18 m 变化，LCR 从 65 到 200。上述证据表明，极小直径桩的极限荷载的评估必须遵循以下考虑：桩的临界荷载，特别是当它嵌入软土时；相反，对于更大直径（大于 20 厘米）的桩，屈曲没有意义，因为 LCR 太大以至于普通细长不超过它。随着桩径的减小。分析结果表明，桩径从 0.06 m 到 0.18 m 变化，LCR 从 65 到 200。上述证据表明，极小直径桩的极限荷载的评估必须遵循以下考虑：桩的临界荷载，特别是当它嵌入软土时；相反，对于更大直径（大于 20 厘米）的桩，屈曲没有意义，因为 LCR 太大以至于普通细长不超过它。随着桩径的减小。分析结果表明，桩径从 0.06 m 到 0.18 m 变化，LCR 从 65 到 200。上述证据表明，极小直径桩的极限荷载的评估必须遵循以下考虑：桩的临界荷载，特别是当它嵌入软土时；相反，对于更大直径（大于 20 厘米）的桩，屈曲没有意义，因为 LCR 太大以至于普通细长不超过它。特别是当它嵌入软土中时；相反，对于更大直径（大于 20 厘米）的桩，屈曲没有意义，因为 LCR 太大以至于普通细长不超过它。特别是当它嵌入软土中时；相反，对于更大直径（大于 20 厘米）的桩，屈曲没有意义，因为 LCR 太大以至于普通细长不超过它。