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The circular helicoid pile (CH pile) is a special-shaped pile with outstanding axial bearing properties developed in the last ten years, its pile-soil interaction problem has nonplanar strain and is non-axisymmetric. The coupled Eulerian-Lagrangian (CEL) method was applied to simulate the entire process of installation, axial compression and pullout loading of the CH pile in undrained clay to assess the interaction between the pile and soil, and the accuracy of the CEL model was verified by in-situ test results. The surfaces of the CH pile were divided into the bottom surface, outer and inner surfaces, with the inner surfaces including compressive and pullout surfaces. The variation in axial forces and moments on the CH pile and its various types of surfaces in the whole process of installation and bearing was clarified and the relative contribution of reacting forces and moments on various surfaces to the total resistance of the pile was evaluated. The stress distribution characteristics of the soil around the pile and the pile-soil interfaces after the installation of the CH pile and under the ultimate limit state were obtained, and then the force states of inner surfaces in the whole process of installation and bearing were analysed.

The circular helicoid pile (CH pile) is a new type of special-shaped pile that has been developed in Japan and South Korea in the past decade and has been widely used in the fields of construction, transportation, natural energy and agriculture due to its excellent compressive and pullout bearing performances. Consequently, this new type of pile has good engineering application prospects. However, as an innovative engineering structure, the CH pile is not widely known by geotechnical engineers worldwide. The geometric structure of the CH pile is similar to a circular helicoid in differential geometry. Therefore, the pile-soil interaction problem cannot be reduced to a plane strain problem or an axisymmetric problem in theoretical research. In view of this, dry silica sand was used as the model foundation in this study, and a model test device and method that can effectively reflect the installation process and loading-bearing service state of CH piles were developed. Under different installation methods, pile structures and foundation soil conditions, 90 model tests were carried out to evaluate the engineering performances of CH piles during the whole process of installation and bearing, including the installation performances during the installation process, the compressive bearing performances under axial compressive loading and the pullout bearing performances under axial pullout loading. Compared with steel sheet piles and steel pipe piles, CH piles have better engineering performance and more economic benefits from the aspects of installation, construction, recycling, timeliness of engineering application, and the relative relationship between bearing capacity and pile mass.