Role of critical normalized roughness in interface shear strength and particle breakage of carbonate and silica sands

Abstract

The roughness of the structural surface serves as a pivotal factor that substantially influences the mechanical properties of the interface. This study identifies a physically interpretable critical normalized roughness governing interface shear mechanism transition and establishes a coupled framework linking friction mobilization with particle breakage evolution. Large-scale three-dimensional pile-soil interface shear tests were conducted on carbonate and silica sands using concrete and aluminum alloy piles with controlled surface roughness to investigate roughness effects on interface shear strength, friction coefficient, and particle breakage under circumferential pile-soil contact conditions. The results revealed that shear stress–displacement curves from all tests exhibited strain-softening. Compared with silica sand, carbonate sand demonstrated higher peak shear strength and more pronounced softening characteristics due to particle breakage and its irregular particle geometry. A critical normalized roughness equal to 0.25 was identified: below this value the friction coefficient increases with normalized roughness, while above it the friction coefficient tends to plateau. Using this critical normalized roughness as a boundary, the relationship between the friction coefficient and normalized roughness can be accurately described by a piecewise power function. Although an increase in surface roughness leads to enhanced particle breakage, the growth rate of breakage diminishes as roughness further increases. These findings provide a physically based reference for interpreting roughness-dependent interface behavior and offer guidance for surface roughness optimization in geotechnical interface design.