Microscopic modeling of colloidal silica stabilized granular contaminated soils

The low-viscosity stabilizer, colloidal silica (CS), is extensively used as a grouting material in the construction of grout curtains to prevent fluid movements. It is a low viscosity and nontoxic material, which is suitable for injection to stabilize/solidify fine grained soils. It is also used in the in situ treatment of hazardous waste as a stabilizer/ solidifier. Once the CS solution is injected into contaminated soil, it moves through the pores inside the soil matrix and initiates the stabilization/solidification process. The viscosity of the CS mixture increases while it moves until complete solidification occurs. In this paper, the transport of CS during injection was simulated at the microscopic level to understand the stabilization/solidification process. The microscopic behavior/movement of CS stabilizer inside anisotropic granular soil during grouting was simulated by numerically solving the Navier-Stokes equation. The change in gel viscosity with time was used to model the movement of CS during injection. A model parameter vmin, the minimum velocity for CS to become a solid, was introduced. The simulation showed that during the grouting of fine sands, solidification starts at the soil surface and expands to fill the majority of voids within 1.2h. The simulation of CS grouting of different soil types, soil compaction levels, and soil anisotropies showed the impact of soil parameters such as grain size distribution, void ratio and anisotropy on velocity contours and the final solidification. This microscopic model can be further improved to be used in the design of grout curtains, especially for the determination of the ability to grout soils and the size of stabilizer plume in such stabilization projects.