DEM Modeling of the Load-Bearing Mechanisms of Rock-Socketed Piles with Soft Interface Materials

The load-carrying capacity of rock-socketed piles depends on the shaft resistance at the pile-rock interface which is governed by the interactions between the pile, rock, and soft interface materials (smear or infill). Despite recent advancements in 3D experimental pile testing of smeared interfaces, the knowledge in this field still remains quite limited primarily due to the experimental limitations, and high costs and fabrication challenges associated with extensive laboratory tests. This study presents a comprehensive numerical investigation to simulate 3D rock-socketed piles with smear using the discrete element method (DEM). By correlating the observations with the experimental x-ray CT images, the interactions between the pile, rock and smear are investigated for various smear area proportions in terms of the micromechanics at the asperity level. The movements of smear and rock debris in the socket and their influence on the various asperity failure modes in relation to the shaft resistance development are evaluated by monitoring the force and damage evolution in DEM. Finally, the calibrated DEM model is utilized to examine the influence of the various smear fabric parameters on the shaft response. Based on the observations, it was inferred that the shear failure mode primarily dictates the interface damage evolution, with a significant contribution from mixed-mode failure involving both tensile and shear damages. Insights from the results indicated that the effect of smear placement on the load-bearing capacity of the pile is found to be minimal compared to the other smear fabric parameters (thickness and area proportion). Moreover, the critical smear thickness to asperity height ratio was determined to be 1.75 beyond which the smear controls the load-bearing capacity of the pile. The discussions presented in this study provide a novel understanding into the smear fabric effect and act as a foundation for further research aimed at improving the reliability and efficiency of rock-socketed pile construction in soft rocks.