Role of particle size and element characteristics on shear response at sandy soil-textured surface interfaces

A fundamental understanding of shear behavior at the interface between foundation elements with innovative surfaces that include bio-inspired or structured element designs is critical in the design of many geotechnical structures. Some geotechnical applications could benefit from the use of surfaces with structured roughness form that mobilize larger shear resistances than conventional interfaces with random roughness form. However, several parameters such as soil properties, particle size, surface roughness, geometry of surface elements may influence the shear behavior at the interface between soil and surfaces with structured roughness which requires further research. To study the possible effects of these parameters on shear resistance, a series of interface direct shear tests were performed for 7 sands with varying particle sizes and four aluminum surfaces (three textured with trapezoidal-like elements and a smooth surface). When the 7 sands sheared against the same textured surface, the shear resistance decreases with increasing element height to mean particle diameter ratio (h/D₅₀) and increases with increasing element-to-element spacing to height ratio (S/h). A parametric study on the geometrical characteristics of surface elements and soil particle size revealed that the h/D₅₀ and S/h ratios could quantitatively capture the interface load-transfer mechanisms between sand and textured surfaces. Based on the results obtained, it was found that the effect of particle size of test sand on shear resistance diminishes as h/D₅₀ and S/h decreases (i.e., surfaces with closely spaced elements). It was also found that, for identical surface characteristics, particle size affects the mobilized resistance: higher shear strengths are achieved when the sand's mean particle diameter (D₅₀) closely matches the asperity (element) height of the textured surface.