Bored PHC nodular piles (BPNP) are an eco-friendly and advantageous option for pile foundations of medium-rise to high-rise buildings. As none of the current methods to estimate the ultimate axial load-bearing capacity is accurate enough for BPNP in engineering practice, this study aims to achieve that objective by developing a new direct SPT method. To that end, we use static pile load test and SPT data of 81 PHC nodular piles collected in Vietnam. The ultimate bearing capacity is interpreted from the load–displacement curve in pile static load tests by various methods to determine the most suitable method for the nodular piles. Furthermore, 8 methods to determine axial load pile capacity directly from the standard penetration test are examined. Each method’s effectiveness is evaluated by comparing its predicted values with the measured values. Finally, the genetic algorithm for function optimization is employed to develop a new direct SPT method that can accurately predict the ultimate axial load-bearing capacity of nodular piles. The reliability of the proposed formula is justified by comparing the proportion of end bearing capacity with other published works. It is verified that the developed directed SPT method outperforms all current methods and could be implemented directly in engineering practice.

钻孔 PHC 球桩 (BPNP) 是中高层建筑桩基的一种环保且有利的选择。由于目前估计极限轴向承载能力的方法都不足以在工程实践中对 BPNP 准确，因此本研究旨在通过开发一种新的直接 SPT 方法来实现这一目标。为此，我们使用了在越南收集的 81 个 PHC 结节桩的静力桩载荷试验和 SPT 数据。通过各种方法从桩静载荷试验中的载荷-位移曲线解释极限承载力，以确定最适合球状桩的方法。此外，还检查了直接从标准穿透试验确定轴向荷载桩承载力的 8 种方法。通过比较其预测值与测量值来评估每种方法的有效性。最后，利用遗传算法进行函数优化，开发了一种新的直接SPT方法，可以准确预测结节桩的极限轴向承载能力。通过将端部承载力的比例与其他已发表的作品进行比较，证明了所提出公式的可靠性。经验证，所开发的定向 SPT 方法优于所有现有方法，可以直接在工程实践中实施。