Abstract: To investigate the influence of pile surface roughness on the bearing capacity and deformation characteristics of a single pile under vertical loading, a series of static loading tests was performed on a self-developed “multifunctional static and dynamic model test system for pile foundation”. Three single model piles with the smooth, random, and ribbed inerratic surface roughness were manufactured and their values of roughness (Rn) were obtained through 3D shape scanning calculation. The test results show that the ultimate bearing capacity and pile stiffness increase with augmenting of Rn, while the settlement of the pile top and its unloading rebound decrease with it. Specifically, the ribbed pile can effectively improve the pile’s bearing capacity and control the pile top’s vertical deformation. The pile side resistance and the strengthening effect of the side resistance near the pile tip also increase with increase in surface roughness. The distribution pattern of pile side resistance evolves from “single hump” to “cone top column” and finally to “slope type” with increased loads on pile top. The value of β  (parameter in β  method) increases with the increase in surface roughness and decreases with the increase in depth. The ultimate pile side resistance and the value of β  of the ribbed pile are far greater than that of smooth and sandpaper piles. These conclusions reveal influence mechanism of the buried depth and surface roughness on the value of β . Pile surface roughness affects the type of load transmission function of the pile tip in saturated sand. For smooth and sandpaper piles, the load transmission function of the pile tip follows a hyperbolic equation, whereas for ribbed piles, it follows a linear equation. These research findings are crucial for fully understanding the laws and mechanisms governing the influence of surface roughness on the bearing capacity and deformation characteristics of single piles.

Key words: pile surface roughness, model test, saturated sand, pile side resistance, pile tip resistance