Groundwater flow below construction pits and erosion of temporary horizontal layers of silicate grouting

Injection of silicate grouting materials is widely used to create temporary horizontal layers for reducing inflow of groundwater at construction sites, in regions with shallow water tables. The erosion of a grouting layer was investigated by means of analytical solutions for groundwater flow and transport within a pit after construction finished. Erosion is assumed to occur by dissolution of the temporary injection layer and subsequent advective transport. Thereby, the hydraulic conductivity changes with time. This paper presents novel analytical solutions and approximate solutions for the major fluxes in the construction pit as a function of the domain settings, aquifer gradient and hydraulic conductivity. In addition, the mass flux and the dilution ratio of erosion-related components leaving the construction pit and entering the aquifer are quantified. Derived solutions are verified against numerical simulations. A sensitivity study shows the impact of domain settings on fluxes and dilution ratio. The results confirm that mass flux of grout components increases with ongoing erosion. Thus, its effect on groundwater quality increases with time after construction ceased.