The contractive behavior and flow failure in saturated binary granular soils have been studied by many as functions of their physical properties [gradation, mean particle size, fines content (FC), and packing quality] and mean effective stress, stress history, and cyclic stress amplitude. Nevertheless, little is known on the interplays between frame elements and fines in loose saturated geocomposite mixtures and also between virgin and added frame elements under cyclic loading. That knowledge shortfall has lent uncertainty to flow potential and compressibility predictions for saturated sands in their natural and engineered forms. In this paper, 36 cyclic undrained triaxial-compression tests were performed to investigate the cyclic behavior and properties of saturated loose sand–silt–tire-derived ground rubber (GR) mixtures and to determine the effects of the GR and almost nonplastic fines on the rate of pore-water pressure buildup. The complex interplay among the angular sand, fines (silt) and GR solids, and pore spaces of varied shape, size, and rigidity are discussed at a microscale and invoking the framework of two conceptual models, small silt and large silt. The control of FC on liquefaction resistance was found to be dependent on the sand and GR particle sizes. The relatively greater elasticity of GR than sand lends a damping effect to frame elements and further improves the liquefaction resistance through relaxation of skeletal stresses and reduces the chance of contact destruction for sand particles.

Colloidal nano-silica (NS) hydrosols are electrochemically stabilized, polymerized amorphous silica in low viscosity solutions, and in the form of hydrated gels, silica globules or pellicles. Compared to applications in concrete technology, the use of silica-based binders for groundwork applications has received little attention. Silica-based hydrosols impose no known direct risks to humans and are generally courteous to the soil health and ecosystem service functions. Their localized impact on microorganisms however needs to be further investigated. To this end, NS hydrosols have a scope for use as an alternative low-viscose material in groundworks. The current understanding of interactions between NS hydrosols and soil (sand) is, however, confused by the limited availability of experimental evidence concerning undrained static flow and large strain behavior. The contributions, presented in this paper, advance the knowledge through experimental testing, molecular modelling, and micro-analytical measurements. Four grades of colloidal NS (1–15 wt.%) were synthesized for grouting medium-dense sub-angular fine siliceous sand specimens. Consolidated-undrained triaxial compression testing was performed on the base and treated sand for isotropic consolidation over the effective stress range 100–400 kPa. Overall, silica impregnation produced improvements in yield and residual undrained shear strengths, restricted unwelcomed impacts of excess pore water pressure, and led to the formation of generally more dilative, strain-hardening behavior. Steady states and static flow potential indices are also studied as functions of confinement level and viscosity of the NS grout.

The contribution of fibers to the strength of fiber-reinforced soils is dependent on multiaxial stress space. This study furthers knowledge on the dependency of steady states on anisotropy in unreinforced and reinforced (with 1.5% microsynthetic fibers) well-sorted sands with different shape and size properties. For this purpose, the direction of principal stress orientation varied from 15° to 60°, for an intermediate principal stress ratio of 0.5 and 1.0 and initial effective consolidation stress of 200 kPa. For this study, 24 undrained torsional shear tests were conducted using a hollow cylindrical torsional shear (HCTS) apparatus. When sands were randomly mixed with fibers, a dilative and strain-hardening behavior governed, and undrained strength generally improved. The samples’ anisotropy decreased, and a distortion of the deviatoric strength envelope was produced by the addition of fibers to the host sand. The results indicated that fiber reinforcement contribution is augmented with the growth of the major principal stress direction. This phenomenon is attributed to the sample loading combination changes from compression to torsion. The fiber strengthening contribution across all principal stress directions was higher in the sand with a larger median grain size (${\mathrm{D}}_{50}$ ) and angularity. Further, an increase in particle shape scale (${\mathrm{r}}_{\mathrm{s}}$ and ${\mathrm{r}}_{\mathrm{r}}$ ) ratios caused the stress-strain curves to approach another and reduced occurrence in specimen anisotropy. Further explanations on the effect of fiber addition are presented.