Effects of Weak-Interface Materials on the Axial Load Capacity of Rock-Socketed Piles: A Numerical Investigation

Abstract Rock-socketed piles (RSPs) have been used to support the heavy loads of civil infrastructure, such as high-rise buildings and bridges, in response to urbanisation challenges. Despite extensive research, engineering practices often use conservative safety margins in designing RSPs, especially when existence of smear (soft materials) at the pile–rock interface is considered to determine the load-carrying capacity. Meanwhile, the synergy between advancements in 3D experimental visualisation techniques and numerical methods is emerging as a promising approach to address challenges in laboratory investigation and numerical modelling of RSPs. In this context, the present study introduces a comprehensive finite element model (PLAXIS 2D) that integrates appropriate constitutive models and interface elements to accurately simulate the interaction mechanisms between the pile, smear, and soft rock. The investigation starts by creating a numerical model to simulate small-scale pile load tests. The calibrated FEM model was then extended to investigate the interface-level mechanisms and ultimate shaft capacity of RSPs with varying smear parameters at both shaft and base of the pile. Based on the investigations, PLAXIS 2D effectively analyses the axial load-bearing mechanisms of smeared RSPs. Detailed parametric studies reveal that smear thickness causes an exponential decline in shaft resistance up to a critical smear thickness to asperity height ratio of 1.75. Changes in smear shape, from quadrilateral to triangular, result in a 20–35% increase in shaft capacity, with smear oriented against the loading direction enhancing resistance. Furthermore, while smear at the base does not affect ultimate shaft loads, it results in an average reduction of 30% in total load capacity corresponding to displacements at ultimate shaft loads, and requires greater displacements to achieve the ultimate shaft condition. Overall, this study serves as a catalyst for incorporating smear effects into the evaluation of serviceability limit capacity, thereby enhancing traditional modelling practices and design methods for RSPs.