Direction-Dependent Skin Friction between Snakeskin-Inspired Surfaces and Piles and Normally Consolidated Clay

Driven or jacked foundation elements typically mobilize similar interface shear strengths when loaded in tension and compression, leading to challenges associated with hard installation conditions when the skin friction is high or excessive settlements when it is small. Snakeskin-inspired surfaces have been shown to address this problem by mobilizing greater skin friction in the cranial direction (i.e., against the scales) than in the caudal direction (i.e., along the scales). However, most of the available data is for interfaces with sands. Thus, this paper investigates the direction-dependent skin friction mobilized between normally consolidated clay and snakeskin-inspired surfaces and piles. Laboratory tests are performed to characterize the effect of the asperity height and length on the interface shear behavior at different normal stresses and drainage conditions. Specifically, tests are performed at sufficiently slow and fast shearing rates to generate drained and undrained conditions. Centrifuge load tests shed light on the effect of the snakeskin-inspired texture on the skin friction magnitude and distribution during installation and tensile loading of piles. In both interface element and pile load tests, shearing in the cranial direction mobilized greater skin friction than in the caudal direction. The interface strength increased with asperity height and decreased with asperity length, and the ratio of length to height captured this effect. The pile load tests indicated a skin friction magnitude that is up to 60% greater during pullout than during installation. Additionally, the cranially pulled piles mobilized skin friction magnitudes that were between 2.8 and 4.1 times greater than those mobilized by an untextured aluminum pile. These findings highlight the potential for using snakeskin-inspired surfaces to optimize pile performance by enhancing pullout capacity while limiting the increase in installation forces in clays.