Evaluating screw-shaft pile composite foundations in round Gravelly soil: A study using model tests and numerical simulations.

Screw-shaft piles have seen extensive adoption in construction and railroad engineering, due to their superior enhanced bearing capacity and cost-effectiveness. While monopiles have been thoroughly examined, composite foundations that include screw-shaft piles have not been studied as extensively. Proper determination of geometric parameters for both the piles and the cushion is a critical aspect of successful design. This paper introduces a comprehensive examination that merges indoor experiments with numerical simulations, aiming to evaluate the bearing capacity, settlement characteristics, and force characteristics of screw-shaft piles under a variety of conditions. This study scrutinizes key components, such as root diameter, pitch, cushion modulus, and the threaded portion's proportion. The research outcomes offer crucial insights for optimizing the design parameters of screw-shaft pile composite foundations. The results indicate that the side resistance of screw-shaft piles initially increases with the threaded section's length, stabilizing at an optimal length of approximately 0.44-0.55 times the pile length (L). Furthermore, although decreasing the pitch improves bearing capacity, it also introduces variations in pile material usage, with optimal bearing performance noted at a pitch approximately equal to the diameter (D). Moreover, screw-shaft piles with thread widths ranging between 0.58D and 0.67D show a significant decrease in stress concentrations, approximately 22 % less than those with a width of 0.5D. By setting the cushion modulus within the 40 MPa-60 MPa range, reduced settlement and optimal pile-soil stress ratios were achieved. These research outcomes provide critical insights into optimizing screw-shaft pile composite foundation design parameters, serving as valuable guidance for designers and engineers in diverse civil engineering projects.