Sodium Silicate Grouting: Mechanisms, Environmental Impacts, and Research Directions

Sodium silicate grouting is a widely used technique for reducing soil permeability and reinforcing unconsolidated soils. Despite decades of use, its field performance remains inconsistent, with efficiency strongly influenced by soil heterogeneity, groundwater composition, and contaminant interactions. In addition, the environmental risks associated with silica gels, such as leaching of diluted grout into groundwater and long-term degradation, are not fully understood. This review, the first comprehensive synthesis since the 1990s, integrates insights from scientific studies, field applications, and industry practice. We examine the coupled processes governing injection, gelation, and post-gelation evolution across micro-, pore-, and field scales, and identify the key hydraulic, chemical, thermal, and environmental parameters controlling grouting performance. Particular attention is given to sand–gel interactions, microstructural development, permeability reduction mechanisms, and factors governing strength enhancement. The review also evaluates environmental impact and discusses the potential of Electrical Resistivity Tomography (ERT) for monitoring grout continuity. Finally, we outline critical research directions needed to develop constitutive relationships for grout properties, improve predictive modelling, and enable more reliable, sustainable, and environmentally compatible applications of silicate grouting.