A transport model for the permeation of colloidal silica

Colloidal silica grout is a relatively new grouting material and as such, it does not fit any current design standard and is missing the empirical knowledge that accompanies conventional grouting materials. Industry uptake seems slowed by (i) the lack of a grout penetration model to inform engineering design, (ii) the lack of laboratory or field data to understand grout penetration in the natural environment, specifically where there are heterogeneous soils or in the presence of in situ cations and (iii) the lack of in-situ validation methods that can demonstrate grout barrier integrity at a commercial scale. This paper presents a transport model to predict the spatio-temporal evolution of in situ colloidal silica grout permeation, accounting for the interaction between the grout and the porewater chemistry during injection. The newly developed viscosity relationship is implemented within a flow and transport model to predict grout permeation. The model’s predictive accuracy is validated against a series of metre-scale, tank-based experiments involving varying soil permeabilities and saline groundwater conditions. Furthermore, this research evaluates the efficacy of Electrical Resistivity Tomography (ERT) as a commercial-scale monitoring tool. Results demonstrate that differential ERT analysis (comparing pre- and post-injection states) successfully delineates the grouted soil volume and barrier integrity. The findings provide a dual-track solution for geotechnical engineering: a numerical framework for design optimisation and a geophysical methodology for field-scale validation.