The structure of screw threaded pile is complex, and its force analysis has always been a difficult research point. To study the friction characteristics of the loess-threaded contact surface, In this paper, 3D printing technology is used to make threaded contact surfaces, and combined with direct shear test. This research analyzed shear stress-strain curves, shear stiffness, internal friction angle, and cohesion of the contact surface, and the influences of dry density, water content, and screw thread pitch changes on the friction characteristic were also discussed. The research revealed the loess-screw thread contact surface experienced nonlinear elastic deformation, plastic failure, and shear slippage during the shear test process. When the dry density decreases, water content increases, and normal stress increases, the nonlinear elastic deformation characteristic of the stress-strain curve intensifies, and the potential of strain softening reduces. The tangential stiffness of the contact surface is positively correlated with dry density and negatively correlated with water content. The cohesion of the contact surface is mainly affected by dry density and water content, while the screw thread pitch has a significant impact on the internal friction angle of the contact surface. Based on the friction characteristics, it is recommended that the optimal screw thread pitch and pile diameter of screw threaded pile be the same.
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