Estimation of interface frictional anisotropy between sand and snakeskin-inspired surfaces

The transmission of loads across the soil-structure mobilizes direction-dependent shear resistance, which can be selectively used to design geo-structures. A previous study confirmed the frictional anisotropy induced by the interface between the soil and snakeskin-inspired surfaces. However, it is necessary to estimate the interface friction angle quantitatively. In this study, a conventional direct shear apparatus is modified, and 45 cases are performed in two-way shearing directions between bio-inspired surfaces and Jumunjin standard sand under three vertical stresses (50, 100, and 200 kPa). The results show that: (1) shearing against the scales (cranial shearing) mobilizes larger shear resistance and produces a dilative response than shearing along the scales (caudal shearing) and (2) higher scale height or shorter scale length exhibits dilative tendency and produces higher interface friction angle. Further analysis is conducted to capture the frictional anisotropy as a function of the scale geometry ratio, which reveals that the interface anisotropy response is more pronounced during cranial shearing in all the cases, and the difference in the interface friction angle for the caudal → cranial test is higher than that for the cranial → caudal test at the given scale ratio.