Experimental study on the effect of surface-projected conditions on the mechanical behavior of pile embedded in sand

Surface-projected piles, such as helical and under-reamed piles, are widely utilized in geotechnical engineering to enhance the load-carrying capacities of pile structures with surface projection part. Despite the use of a wide variety of surface-projected conditions, detailed investigations considering various dimensions and angles of surface-projected piles remain limited in the current literature. This study aims to assess the effects of surface-projected widths w_p (10 mm, 20 mm, 40 mm) and angles θ (18°, 27°, 45°, 90°) on pile penetration resistance using a two-dimensional model and PIV analysis. Wider projections increased resistance, with a maximum of 1.84 kN—57% higher than conventional piles in the model ground. Penetration resistance was proportional to width at 90°; for w_p = 20 mm, penetration resistance decreased with increasing θ, while for w_p = 40 mm, it increased. Theoretical ultimate bearing capacity calculations emphasize differences from experimental results due to neglected shaft friction. Residual penetration resistance and particle displacement were observed for w_p of 20 mm and 40 mm after failure. This study provides insights into optimizing surface-projected pile design and understanding ground failure mechanisms.