Bearing mechanism and design optimization of screw piles in loess area

This study aims to analyze screw piles to investigate the behavior of a screw pile through its load transfer, failure mode, and estimated bearing capacity and to provide recommendations for the maximum efficiency of the screw pile in a structure. To address this, a numerical model was developed using the 2D Finite Element Method (FEM) in ABAQUS. The criterion for soil strength was the Mohr-Coulomb criterion. The effects of the pile-soil interface characteristics, shear strength of the soil, and structural dimensions of the screw pile on its bearing capacity were investigated. The numerical model was validated using experimental data from other studies, with a difference of less than 20%. The results showed that the key factors affecting the vertical bearing capacity of the screw pile were the soil shear strength index, screw spacing, and screw thickness. Moreover, an analysis of plastic zone formation was conducted to provide clarity on the screw pile failure mode and vertical load transfer. Compared with practical engineering tests, the interaction between the pile and soil was analyzed, and the q-s curves of the screw and circular straight piles were obtained. The results were consistent with the continuous arch failure surface theory of the soil around the screw pile. The comparison indicated that the screw pile had a better bearing capacity of approximately 1.5-2 times that of the circular straight piles. It was also found that the failure mode tended to be linear along the soil when the pitch spacing was reduced (Smin = 0.6 m), and it tended to be concentrated at the pitch when the spacing was increased (Smax = 1.2 m). The results provide useful insights into the behavior of screw piles in loess foundations and may serve as a reference for preliminary design considerations.