In the current practices, the evaluation method for the bearing capacity of small-diameter spiral piles is a conservative method performed on the safe side, since it does not consider the integration effect with the surrounding ground due to rotational press-fitting. In addition, the evaluation method for the bearing capacity of spiral piles subjected to combined loads has not been established. In this study, a series of push-in, pull-out, and horizontal loading tests on spiral piles constructed on a soft viscous ground is conducted, and a method to easily consider the integration effect of the surrounding ground by rotational press-fitting is proposed. Subsequently, based on the proposed method, small-diameter spiral piles are modelled with a FEM analysis, various test results are reproduced, and coefficients for considering the integration effect of the surrounding ground in a numerical analysis are established. With the same FEM analysis method, using the established coefficients, the bearing capacity characteristics of vertical and batter spiral piles for combined loads are obtained. Finally, based on the results, formulas for the bearing capacity envelopes in the H-V-M space are proposed and the accuracy of the formulas are verified.

在目前的实践中，小直径螺旋桩承载力的评价方法是一种保守的方法，在安全方面进行，因为它没有考虑旋转压装与周围地基的结合效应。此外，尚未建立螺旋桩联合荷载作用下承载力的评价方法。在这项研究中，对在软粘性地基上建造的螺旋桩进行了一系列推入、拔出和水平加载试验，一种通过旋转压装轻松考虑周围地基整合效果的方法是建议的。随后，基于所提出的方法，通过有限元分析对小直径螺旋桩进行建模，再现了各种测试结果，建立了数值分析中考虑周围地面综合效应的系数。采用相同的有限元分析方法，利用所建立的系数，得到了竖向和斜螺旋桩在组合荷载作用下的承载力特性。最后，在此基础上，提出了HVM空间承载力包络的计算公式，并验证了公式的准确性。