Experimental study and micromechanical modeling of silica sand-pile interface shearing behavior: effects of relative density, interface roughness, normal stress, and mean particle size

The interface shearing behavior between the pile and seabed soil are crucial for the load-bearing capacity and stability of offshore platforms and wind turbines. This study investigated the interface shearing behavior by combining experimental analysis and micromechanical modeling, with a focus on the effects of relative density (Formula presented), normal stress (Formula presented), large interface roughness (Formula presented), and mean particle size (Formula presented). The experimental results show that both (Formula presented) and (Formula presented) have significant effects on both the peak and residual shear strength. Increasing (Formula presented) enhances the interlocking effect between soil particles and the interface, thereby contributing to higher frictional resistance. Under conditions of high roughness, the interlocking action reaches a state of saturation such that further increases in (Formula presented) do not induce meaningful changes in the friction angle. At this stage, the interface friction angle stabilizes and approaches the value of pure sand. This behavioral trend, validated across an extended range of (Formula presented) (up to 6.96), not only corroborates prior findings regarding roughness effects but also expands the understanding of such mechanisms. However, the critical (Formula presented) threshold for the saturation of peak friction angles exhibits a strong dependence on (Formula presented), with smaller (Formula presented) corresponding to higher critical thresholds. Specifically, the critical thresholds are approximately 1.52 for a (Formula presented) of 0.46 mm, 0.72 for a (Formula presented) of 0.97 mm, and 0.36 for a (Formula presented) of 1.39 mm. Furthermore, the proposed micromechanical model combining contact mechanics with statistical descriptions of rough interfaces shows that both (Formula presented) and (Formula presented) significantly impact interface strength. The comparison between experimental data and model predictions demonstrates the model applicability and provides a deeper understanding of soil-pile interaction mechanisms.