Abstract: Helical piles have gained widespread application in engineering foundations such as transmission lines and photovoltaic supports. However, the mechanism by which the installation rate affects the installation effect and bearing capacity characteristics of helical piles remains unclear. This study conducted model tests on the installation and uplift resistance of helical piles in sandy soil foundations. The relationships between the advancing ratio and torque, downward pressure of the helical piles were analyzed. A modified calculation method for the correlation coefficient of ultimate bearing capacity-torque-downforce was established. The reliability of the modified calculation method was verified through comparative analysis with experimental results from the literature and other calculation methods. The findings indicate that the advancing ratio has a linear relationship with both the installation torque and downward pressure of the helical piles, with a greater impact on the installation torque. Reducing the advancing ratio during the installation process can effectively enhance the uplift bearing capacity of the helical piles. Under the experimental conditions, the ultimate uplift capacity at an advancing ratio of 0.6 can reach 2.9 times that at an advancing ratio of 2. The proposed calculation method for the ultimate bearing capacity-torque-downforce correlation coefficient in sandy soil foundations exhibits an overall calculation error of less than 30%, demonstrating good accuracy and applicability.

Key words: helical pile, driving torque, downforce, advancing ratio, ultimate uplift capacity