Micro-to-Macro Exploration of Shear Behavior at Sand-Steel Interfaces

Accurate prediction of shear behavior at sand-steel interfaces is crucial for the design of friction piles, where load transfer depends on interface resistance. Traditional models often overlook the effects of particle-scale morphology, leading to limited predictive capability. This study aims to investigate the role of grain-scale features in governing shear response through a multiscale experimental approach. Macroscopic interface shear tests were conducted using two particulate materials differing in angularity and roughness to evaluate frictional behavior under varying normal loads. Additionally, micromechanical shear tests were performed on individual sand particles using a custom apparatus to isolate the influence of mesoscale geometry, quantified by the Mesoscale Interlocking Index (MII). Results showed that angular particles developed higher shear strength and surface abrasion, while smoother grains exhibited lower and stable friction. A strong correlation was observed between MII and contact-level friction, highlighting the need to incorporate mesoscale descriptors into geotechnical interface modeling frameworks.