Abstract
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.
Highlights
Monotonic loading of loose, saturated sand deposits may lead to the abrupt loss of shear strength and, as such, continues to be one of the most challenging problems in ground engineering [1,2].The sudden strength loss that occurs for undrained conditions is known as static flow or softening [3,4] and takes place before the effective stress path reaches the failure line
Our findings indicate that grouting sand with NS leads to a gradual transformation of the base sand into a geocomposite possessing stiffer, more brittle, and more dilative stress-strain behavior
For the EU zone, they showed that the predicted environmental concentration (PEC) of NS in surface water ranges from 0.053–3.3 μg/kg, and as high as 60 μg/kg in shallow soils
Summary
Monotonic loading of loose, saturated sand deposits may lead to the abrupt loss of shear strength and, as such, continues to be one of the most challenging problems in ground engineering [1,2]. In making provision for establishing or extending the built settings on loose sands, research into binary geomaterials (saturated sand with various fines contents for the present investigation) led to the development of a diverse range of chemical stabilization techniques. These techniques share uncertainties inherited from the contradictory views on the impacting role of the fines content in sand. The impact of sand and silica-floc size, and shape are discussed b contrasting macro-scale findings with those of standard Toyoura and Fujian sands, and through qualitative particle-scale events The latter gains stimulus from two directions. The findings from this work will be of particular interest to practitioners with an interest in employing NS grout for remediation of distressed sandy earth systems
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