Compressive bearing behavior and pile–soil interaction of spiral-ribbed thin-walled concrete-filled steel tube piles

To address the issues of excessive steel consumption and complex fabrication associated with traditional helical piles, this study proposes a novel type of concrete-filled thin-walled steel tubular pile with spiral ribs. This new design reduces steel usage by over 40 % while significantly improving manufacturing efficiency. Vertical compression tests were conducted on eight model piles to investigate the influence of spiral rib width and pitch on pile–soil bond–slip behavior. Results indicate that the ultimate bearing capacity of the spiral-ribbed pile reaches 12.7 kN, nearly six times that of a conventional steel tube pile (2.1 kN). The failure mechanism is characterized by circumferential shear-slippage along the spiral ribs at an angle of approximately 45°, with soil compaction observed beneath the ribs and a localized loosening zone forming above. A pronounced slip interface was observed around the pile shaft. Compared to straight-shafted piles, the spiral configuration maintains superior load-bearing performance even in the post-slip stage, demonstrating a strong safety reserve. Increasing the spiral rib width from 15 mm to 55 mm enhanced the ultimate bearing capacity by 81.4 %, while reducing the pitch from 300 mm to 165 mm led to a 15.9 % increase—indicating a more pronounced influence of rib width on performance. An optimal spiral configuration is recommended with a width-to-diameter ratio (D/d) of 2.0 and a pitch-to-diameter ratio (S/D) of 1.0. Based on the stress distribution in the surrounding soil, the influence radius extends to approximately 1.4 D, suggesting a minimum pile spacing of 2.8 D in practical engineering applications. Furthermore, a full-scale numerical simulation of pile–soil interaction was conducted, revealing that increasing the pile length from 12 m to 18 m results in the largest gain in ultimate bearing capacity—from 698 kN to 1554 kN. However, stress concentration occurs at the junction between the steel tube and spiral ribs, shifting the failure mode from soil failure to structural failure of the pile body. Therefore, it is recommended that pile length be limited to within 18 m. Finally, a theoretical model for calculating the compressive bearing capacity of spiral-ribbed concrete-filled steel tube piles is established based on the limit equilibrium theory. The findings of this study provide a theoretical foundation for the engineering application of this novel pile type.