Permeation grouting of low-permeability silty sands with colloidal silica

Permeation grouting is used to fill the voids in soils with particulates for the purpose of improving soil strength. The technique has been predominatly used for cohesionless soils, however due to nanotechnological advancements in colloidal silica, its application to other soil types has more recently gained attention. Given sands with high silt fractions are a common geotechnical deposit, permeation grouting using colloidal silica is potentially an attractive improvement technique, yet has received limited attention. Therefore, this paper seeks to investigate the transport properties of colloidal silica in low-permeability silty sand, in terms of the effective grouting penetration range and peak strength. To this end, permeation injection is applied on low-permeability silty sand in a laboratory setting and then direct shear tests are undertaken. The results indicate colloidal silica concentrations should be greater than 10% to meet water resistance and strength requirements, while lower than 30% to ensure a uniform distribution of grout and adequate penetration. A low injection pressure of between 45 and 55 kPa, and between 65 and 75 kPa, is found to be suitable for permeating 20% and 30% concentrations of colloidal silica, respectively. After 7 days of curing time, silty sand at natural moisture content and treated with a 20% concentration of colloidal silica shows an increase in peak strength of between 58.1% and 78.4%, which increases further with curing time. A 20% concentration of colloidal silica is recommended for treating silty sand with a coefficient of permeability in the range 10−6 m/s, based on both injection range and peak strength after treatment. These findings may guide the practice of permeation grouting for low-permeability soils.