A numerical study on column experiments of silicate grouting

Abstract

In civil engineering, soil improvements by silicate grout are often used to reduce soil permeability or to increase soil strength. Silicate grout is injected into the soil via pre-installed tubes, acting as a point source. After injection, the silicate grout will harden, forming a gel in the pore space of the soil. Silicate grout has been extensively in experimental studies on grout itself or in column experiments. In previous studies on column experiments studied in other literature, ground and sand are often mixed a priori to packing the column, rendering perfect laboratory conditions, which are often unrepresentative for processes of grout injection into the subsurface, at the field scale. Therefore, this research investigates how column experiments on grouting should be prepared in order to mimic field conditions as much ass possible, while keeping the experimental setup practical. This investigates column experiments by numerical modelling of these experiments. Dilution of grout is mimicked using an equation to change the hydraulic conductivity based on the concentration of grout present. First, different injection scenario are tested, to study grout distributions depending on location of injection. Then, a sensitivity analysis is performed for hydraulic parameters, such as injection volume, dispersivity and hydraulic conductivity. Results indicate that injecting grout in the center of the column or at the boundary give realistic grout distributions as opposed to a prior mixing. Discharge throughout the column is skewed, with more discharge flowing through the edges of the column. Sensitivity analysis showed that parameters like dispersivity, starting hydraulic conductivity value and the porosity have a minor influence on concentration distribution and discharge. Looking at fluxes through the column for both injections gives similar results. Based on this research, we recommend to conduct column experiments using center injections, based on an injection volume of 54% the pore volume. This will minimize both boundary effects and flow around the edge of the grout.