Simulation of Colloidal Silica Grout Injection Using Shear Effects

Abstract

The colloidal silica grout systems are being investigated for environmental containment barriers and ground improvement. Colloidal silica (CS) grout system behaves as a fluid but reacts after a predetermined time to form a solid, semi-solid or gel. These solid or semi-solid gels offer several orders of magnitude reduction in hydraulic conductivity in the porous media. A numerical model is developed to simulate chemical grouting into porous media by combining a groundwater flow simulation model (MODFLOW) and a 3D multi-species reactive transport model (RT3D). The methods to estimate the grout gel viscosity as a function of gel cure time (gel age), shear rate, and grout concentration are incorporated. The non-uniform gel viscosity is indirectly incorporated into MODFLOW by changing the effective hydraulic conductivity in each cell. The present model is used to analyse the experimental observations on colloidal silica grout injection into a sand column. The model was able to reproduce the observed injection pressures to a large extent. It has been shown that the shear effect needs to be incorporated in the grout gelation model. The model will help in better understanding the physics of grouting, the processes taking place and identifying the parameters.