Effect of electrokinetic method on improvement of loose sand by colloidal silica

Abstract

Improvement of saturated loose sand in developed sites which are susceptible to liquefaction phenomena requires passive stabilization. Colloidal silica, whose nanoparticles have a superficial charge and could be mobile by a small driving force, has been used for this kind of soil improvement. This study investigated the effect of an electric field in colloidal silica injection in Firouzkooh sandy soil by creating coupled electric and hydraulic flow. With establishing a direct electrical field in a soil sample, the influence of electrophoretic on introducing nanosilica particles in the sand sample was evaluated against the hydraulic flow. The unconfined compression strength of the injected specimens was evaluated. The experiments were carried out on two different grain size distributions of sand. The silica grouts with 10% and 30% of colloidal silica by weight were injected under the electric gradients of $1.5{~}^{v}\!\left/ \!\!{~}_{cm}\right.$ and $2{~}^{v}\!\left/ \!\!{~}_{cm}\right.$. In addition, two other types of grouts with ionic strength of 0.1 was also investigated, and all the grouts pH was adjusted at 9. The results show that the samples with salination and higher ionic strength did not meet stabilization. In contrast, the strength of other specimens increased, making the electrophoretic mobility much more dominant than the hydraulic regime. Also, a comparison between two different grain size distributions shows that the smaller the soil grain size, the greater the unconfined compressive strength of the soil.