螺旋挤土桩下旋成孔过程的颗粒流数值模拟

卵砾石地层可压缩性低、抗剪强度大，水泥土搅拌桩工法在应用于卵砾石地层时存钻进困难、钻具磨损大等问题。为确定卵砾石地层条件下钻头形式的最优布置，基于离散元法(DEM)，对不同切削叶片数量、切削叶片角度、截齿布置形式、钻头中心底部布置形式、机械压力工况下，搅拌桩机钻头钻进卵砾石地层的物理过程进行三维动态仿真模拟，并分析研究了不同钻头布置形式对钻进效果的影响。计算结果表明：钻头切削叶片数量的增加会提高钻进阻转矩，但是会增强钻头的定心能力。设置截齿的钻头钻进阻力矩并无明显提高，但钻进速度有一定程度的提高。钻头切削叶片角度的提高会增加钻进阻力矩，但过低或者过高的切削叶片角度均会降低钻进速度。适当提高钻进压力可提高钻进速度，但须考虑动力装置的功率及扭矩输出能力。三切削叶片、高切削叶片角度、设置三截齿的高效率钻头在应用于北京市某项目卵砾石地层时效果良好，文章提出的方法可以为其他工程的施工机械选型提供参照依据。

A discrete numerical model for granular assemblies

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.