In geotechnical engineering, bioinspired ideas such as snakeskin-inspired solutions for frictionally anisotropic continuum materials have been receiving increased attention due to their ability to create resilient and efficient geomaterial-continuum interfaces. Several studies have found that snakeskin-inspired continuum surfaces mobilise significant frictional anisotropy with different soils. However, studies on the effect of snakeskin-inspired patterns on other continuum geomaterials, such as rock surfaces, which can have promising applications like friction rock bolts, are rare. This study aims to address this gap by investigating the effect of snakeskin-inspired patterns on the shear behaviour of soft rocks, which is simulated by Plaster of Paris (PoP). For this purpose, snakeskin-inspired continuum surfaces with surface patterns inspired from the ventral scales of a snake with five different scale angles (10 degrees, 13 degrees, 16 degrees, 19 degrees and 22 degrees) were 3D printed with Polylactic Acid (PLA) polymer using a Fused Filament Fabrication (FFF) 3D printer. The interface shear behaviour of these surfaces with PoP was investigated using a customised interface shear testing apparatus under three normal loads: 1000 N, 2000 N and 3000 N. The results of the tests confirm that snakeskin-inspired patterns on continuum material mobilise substantial anisotropic friction and that the interface shear response depends on the shearing direction and the scale angle. The shearing direction significantly affects the peak and post-peak shear behaviour and the strain softening behaviour of the snakeskin-inspired interfaces. The study yields promising results for applying snakeskin-inspired patterns to create rock bolts with direction-dependent friction and enhances the existing knowledge in bioinspired geotechnics.

Understanding direction-dependent friction anisotropy is necessary to optimize interface shear resistance across soil-structure. Previous studies estimated interface frictional anisotropy quantitatively using contractive sands. However, no studies have explored how sand with a high dilative tendency around the structural surface affects the interface shear response. In this study, a series of interface direct shear tests are conducted with selected French standard sand and snakeskin-inspired surfaces under three vertical stresses (50, 100, and 200 kPa) and two shearing directions (cranial -> caudal or caudal -> cranial). First, the sand-sand test observes a higher dilative response, and a significant difference between the peak and residual friction angles (phi peak - phi res = 8 degrees) is obtained at even a lower initial relative density Dr = 40%. In addition, the interface test results show that (1) shearing against the scales (cranial shearing) mobilizes a larger shear resistance and produces a dilative response than shearing along the scales (caudal shearing), (2) a higher scale height or shorter scale length exhibits a higher dilative tendency and produces a higher interface friction angle, and (3) the interface anisotropy response is more pronounced during cranial shearing in all cases. Further analysis reveals that the interface friction angle and dilation angle are decreased with the scale geometry ratio (L/H). For L/H values between 16.67 and 60, the interface dilation angle varies between 9 degrees and 4 degrees for cranial first shearing and 3.9 degrees-2.6 degrees for caudal first shearing. However, the difference in dilation angle within the same shearing direction is less than 1 degrees.