Experimental Evidence of the Effectiveness and Applicability of Colloidal Nanosilica Grouting for Liquefaction Mitigation

Abstract

The low viscosity and the ability to control solidification rate make colloidal nanosilica grout an excellent ground-improvement solution which is functional for different engineering purposes. A comprehensive experimental programme was performed to test the effectiveness and applicability of low-pressure injection of aqueous nanosilica suspensions against seismic liquefaction and to provide the experimental basis for the design, execution, and control of treatments. Scanning electron microscope and X-ray diffraction tests carried out on samples prepared with variable dosages enabled analysis of the microstructure of the original material and grouted sand. The influence of the grout composition on the solidification rate, viscosity, and shear strength of the treated sand was evaluated with preliminary tests to optimize the use of material. The efficacy of treatment in terms of stress-strain response and liquefaction resistance was investigated with a series of drained monotonic and undrained cyclic triaxial tests. A quality control procedure based on sonic wave transmission was established by performing bender element tests on samples cured for different times. The intent was to find the trade-off between a cost-effective use of materials and the mechanical performance of the treated sand.

Effects of Colloidal Silica Grouting on Geotechnical Properties of Liquefiable Soils: A Review

“…As unanimously observed in the literature, regardless of tested materials and testing conditions (i.e., test type, adopted failure criterion, specimens' dimensions, formation method and relative density, soil characteristics, CS characteristics, etc. ), the liquefaction resistance of treated material is higher than that of the untreated one, and increasing silica content usually leads to higher liquefaction and deformation resistance, both increasing as samples' age increases [14,23,25,37,38,47,49,50,61,64,66,[68][69][70]107]. The axial strain is not symmetric about the zero strain axis (shifted towards the extension region) [23,64,[68][69][70].…”

“…Krishnan et al [50] found that both damping ratio and initial shear modulus significantly increased for treated samples with increasing curing time. Salvatore et al [49] showed that the shear wave velocity was greater for treated than for untreated sand and observed an increase over time of the shear wave velocity measured by bender element tests on treated sand. This agrees with the increase in gel strength as curing time increases.…”

“…A colloidal silica grout is a low-viscosity and harmless solution which increases its viscosity over time forming a colloidal silica gel [44][45][46]. The resulting colloidal silica gel act as a filler/binder among soil particles, stabilizing the material [14,24,[47][48][49][50]. Initially and for some time, depending on a rheological behavior that can be controlled and designed, the CS grout can be moved through highly permeable media, like sands, just by natural or groundwater flow supplied without the need of high injection pressures, allowing minimization of negative side-effects on the surrounding environment [23,51,52].…”

“…Published data generally agree that the liquefaction resistance of grouted soil improves due to soil grouting, and that the level of improvement is directly related: (i) to the amount of silica particles diluted in the stabilizing grout; (ii) to the time between the end of the gelation process and the beginning of testing (known as curing time), increasing as both these factors increase [14,[23][24][25][37][38][39][47][48][49][50][60][61][62][63][64][65][66][67][68][69][70]. The same findings apply for grouted material subjected to static loading conditions [14,37,[48][49][50]60,61,[63][64][65]67,[69][70][71][72][73][74][75][76]. The behavior of grouted soil under dynamic loading at low-medium strain levels has been much less analyzed [77][78][79].…”

“…Salvatore et al [49] performed cyclic triaxial tests on silica sand (D 50 = 0.303 mm, C u = 1.6, G s = 2.65). Specimens were formed by dry sand deposition followed by grout permeation (no preliminary water saturation) (D r = 20.6-61.2%, 140/70 mm height/diameter; curing time 5 d; effective consolidation pressure 100, 200 kPa; CS content: 5, 10%).…”