Role of surface roughness in load transfer of rock-socketed piles: a 3D-Printed interface investigation

Deep rock-socketed piles (DRSPs) play a vital role in deep foundation engineering, where the pile-rock interface (PRI) behavior critically governs the bearing performance and safety of the pile. To address the limited understanding of the load-transfer mechanism in DRSPs, five sets of laboratory model tests were conducted to simulate the bearing behavior under varying PRI roughness factor (RF). The tests revealed a consistent failure mechanism across different RF conditions: radial cracks formed on the bedrock surface, asperities at the PRI were sheared off, and punching failure occurred at the pile top. With increasing RF, the number of cracks and the volume of sheared rock increased, while the depth of shear failure at the pile tip decreased. The base angle of the triangular failure zone progressively shifted from 45° toward 90°. Displacement measurements indicated that pile tip settlement was inversely related to RF. A higher RF was associated with a greater ultimate bearing capacity of the pile. In addition, the attenuation rate of axial force along the pile shaft increased with RF. Shaft resistance was mobilized earlier in the shallow section compared to the deeper section. As RF increased, the ultimate shaft resistance provided by the PRI also rose, thereby improving the overall bearing capacity of the DRSPs. The findings from this experimental study offer valuable insights for the design and construction of DRSPs.