Skin Friction Directionality in Monotonically-and Cyclically-Loaded Bio-inspired Piles in Sand-Article

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The study examines whether pile surfaces inspired by snake belly scales can produce different skin friction depending on the direction of movement. Such directionality could help resolve a foundation-design trade-off: low resistance eases installation, while high resistance improves tensile capacity.<br /><br />The authors conducted 12 centrifuge pile tests in loose and dense Ottawa sand, comparing textured piles with a smooth reference. Piles were installed by pushing or driving and then pulled out; two tests also involved cyclic loading. The asymmetric surface asperities were oriented so soil movement either opposed them (cranial direction) or followed them (caudal direction).<br /><br />Textured piles consistently mobilized greater skin friction in the cranial direction. During pushing, cranial installation produced higher shaft resistance; during driving, it generally required more blows per meter. Cranial pullout resistance exceeded caudal resistance by 82–198%, depending on the test conditions. Cranially pulled textured piles also developed substantially greater resistance than the smooth reference piles. Shorter asperities generally increased resistance, while driven piles mobilized greater pullout resistance than pushed piles. During cyclic loading, resistance and pile stiffness degraded, although their magnitudes were generally greater in the cranial direction.<br /><br />The findings suggest that directional surface textures could be designed to reduce resistance during installation while increasing capacity under later tensile loading. They may also help manage cyclic pullout behavior, which is relevant to offshore foundations. However, the results come from centrifuge tests in dry sand. The authors recommend instrumented and full-scale field tests, development of design relationships, and practical manufacturing methods before adoption in engineering practice.

Keywords

directional skin friction

pile surface texture

snake belly scales

centrifuge pile tests

Ottawa sand

shaft resistance

pullout resistance

offshore foundations

cyclic loading

foundation design