STUDY ON STRUCTURAL PARAMETERS OF CEMENT SOIL MIXING PILE DRIVER BIT IN GRAVEL STRATUM BASED ON DISCRETE ELEMENT METHOD

The gravel stratum has low compressibility and high shear strength. When the cement soil mixing pile method is applied to the gravel stratum, several issues arise, including difficult drilling and significant wear of drilling tools. In order to determine the optimal arrangement of the bit form under gravel stratum conditions, a simulation of the physical process of a mixing pile driver bit drilling into gravel stratum was conducted using the discrete element method(DEM). The simulation considered different factors such as cutting blade number, cutting blade angle, pick arrangement, bit center bottom arrangement, and mechanical pressure. The study analyzed and explored the influence of different bit arrangements on drilling effectiveness. The calculation results indicate that increasing the number of cutting blades enhances the centering ability of the bit but also increases the drilling resistance torque. Adding picks to the bit does not significantly improve the drilling resistance torque, but it enhances drilling speed to a certain extent. Increasing the cutting blade angle of the bit will raise the drilling resistance torque, and extreme cutting blade angles, whether too low or too high, reduce drilling speed. Properly increasing the drilling pressure can improve drilling speed, but the power and torque output capacity of the power unit must be considered. The study suggests that a high-efficiency bit with three cutting blades, a high cutting blade angle, and three picks demonstrates good performance when applied to the gravel stratum of a project in Beijing. The method proposed in this paper can serve as a reference for the selection of construction machinery in other projects.