Directionally dependent strength and dilatancy behavior of soil–structure interfaces

Abstract

Soil-structure interfaces typically exhibit a shear behavior that is independent of the direction of relative displacement due to symmetry in the solid material's surface profile. This experimental study investigates the interface shear behavior of surfaces with asymmetric profiles inspired by the scales of snake skin. The results of shear box interface tests on two sandy soils indicate that the peak and residual interface shear strengths and dilatancy are greater when the soil is displaced against the sharp edges of the asperities (cranial direction) than when the soil is displaced along the asperities (caudal direction). The experimental results indicate that the effect of asperity geometry on the interface shear response can be captured with the ratio of asperity length to asperity height (L/H). Analysis of the stress-dilatancy behavior indicates that interfaces with a relatively short asperity length follow a classical flow rule developed for soils. However, the relationship between the mobilized stress ratio and the dilatancy rate is shown to be a function of the shearing direction and asperity geometry. Implementation of snake skin-inspired profiles on the surface of geotechnical structures may provide benefits in performance and efficiency during installation and service life. In general, the results of this study indicate the behavior of the soil-structure interfaces sheared in the cranial direction is similar to that of interfaces between soil and fully rough surfaces. In contrast, the behavior of the soil-structure interface sheared in the caudal direction shares characteristics with that of interfaces with smooth surfaces, including the mobilization of smaller a interface strength and dilation.

Interface Frictional Anisotropy of Dilative Sand

“…Indeed, the changing trend of interface friction angle is affected by the starting shear direction while the shearing sequence has no effect on the interface friction angle. Previous studies 16,21 revealed that volumetric contraction at the trailing end of the scale during the starting shearing densified soil around the scale, difference in the interface friction angle between the cranial and caudal shearing directions was pronounced depending on the starting shearing direction, and thus the caudal first-caudal second shearing sequence produces larger friction difference than the cranial first-cranial second shearing sequence. However, the current study observes that the interface friction angle in the first shearing cycle is almost identical to that in the second shearing cycle, and thus densification effect during the first shearing is diminished.…”

“…Inspired by the frictional characteristics of snakeskin, many studies have replicated the ventral scale geometry to achieve the desired frictional resistance during soil-structure interactions in various geotechnical engineering applications 5,[13][14][15][16][17][18] . The frictional anisotropy induced by the bio-inspired surfaces was qualitatively analyzed using a conventional direct shear apparatus under a single vertical stress of 75 kPa 5 .…”

“…The bioinspired pile pulled out in the cranial direction produces less vertical displacement and higher skin friction resistance than the caudal direction with smooth surface pile 18 . In addition, other studies explored the interfacial shear behavior between various sands and bio-inspired surfaces during the two-way interface direct shear tests 16,21 . Those sands showed pronounced contractive tendencies due to more rounded particle shape, and dependency of interface behavior on stress history.…”