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.

In Australia, most rail systems are constructed along the coastal line, traversing soft soil deposits that can cause a series of track instabilities, including excessive plastic deformation and mud pumping. For this reason, the subgrade is considered one of the most critical components of the railway infrastructure, and the accurate prediction of its undrained shear behaviour is of utmost importance to ensure track integrity and safety over time. The subgrade is composed of naturally deposited soil, which may be modified using compaction or consolidation techniques to improve its bearing capacity. In each method, the soil presents a unique arrangement of particles, groups of particles, and voids (referred to as fabric), which govern the response of subgrade soils to the substantial loads imposed by moving trains. For this study, samples of clayey subgrade soil were collected from a site where track degradation had been reported. The soil was reconstituted using slurry consolidation and compaction methods to create different fabrics. A series of undrained cyclic triaxial tests were then carried out to investigate the influence of specimen preparation methods on the shear behaviour of soil. Differences in soil fabric were assessed through X-ray microcomputer-tomography (micro-CT), providing insights into the variations observed in the cyclic response. Based on the findings, it is evident that fabric plays a crucial role in the shear behaviour of subgrade soils and should, therefore, be considered in railway infrastructure design.

This study characterises the effects of naturally varying organic content on the compression and shear behaviour of a marine silty-clay from the Netherlands. Index properties and mechanical properties are determined through laboratory tests, including oedometer and multistage loading-unloading triaxial stress paths. The results indicate a significant impact of the organic content on the compression response, with both the loading and reloading indexes increasing as the loss on ignition increases from 3% to 7%. Additionally, the study suggests a directional response of the compression behaviour, with the loading index increasing with the stress ratio. The influence of the organic content on shear strength appears to be less significant. No brittle response is observed during shearing, and a similar ultimate stress ratio is attained by all samples. However, a unique critical state line can only be identified for samples with similar organic content, as its intercept and slope are found to increase with increasing organic content. The experimental results from stress paths at constant stress ratio reveal an anisotropic prefailure plastic deformation mode, which depends on the previous stress history and loading direction. This suggests that the stress-dilatancy relationship cannot be formulated as a unique function of the stress ratio. The high-quality experimental data presented in the study enlarge the database on soft organic soils in view of the development of advanced constitutive models.

While the fabric of soil can significantly influence its behaviour, the effect of varying fabric parameters on the subgrade shear response is still not well understood. This study creates soil specimens with different fabrics which are then captured through X-ray microscopic-computed tomography scanning and quantified by image processing techniques. A comprehensive laboratory investigation is conducted to understand how the soil fabric affects its monotonic and cyclic shear behaviour. The results indicate that the consolidation method creates a more homogeneous fabric with mainly small-to-medium interconnected pores, whereas the compaction technique creates significantly large and mostly inter-aggregate pores with lower connectivity. In this regard, the consolidated specimens exhibit an elastic-perfectly plastic behaviour, while the compacted specimens show strain-hardening transformation during isotropic monotonic shearing. Under anisotropic conditions, the compacted specimens exhibit a greater strain softening response and excess pore pressure than the consolidated specimens because they have a weaker fabric. Furthermore, the compacted specimens show a smaller threshold strain at a lower critical number of cycles due to the collapse of large pores. These current findings prove the decisive role that soil fabric plays in determining the shear response and failure of subgrade soils.