Infiltration through an Artificially Hydrophobized Silica Sand Barrier

Applying a layer of artificially hydrophobized soil barrier was proposed to minimize water infiltration in landfill covers and hence to reduce the formation of leachate. Existing research has focused on the hydrological behavior of hydrophobized soil, but its effectiveness in reducing or delaying infiltration to the underlying unsaturated soil has rarely been studied, especially under extreme wetting conditions. The objective of this study was to perform a series of parametric infiltration tests to quantify the water flow patterns within hydrophobized barriers and then evaluate their effects on the infiltration characteristics of loosely compacted silty underlying or overlying sand. The barrier was made of silica sand that was hydrophobized by 3% dimethyldichlorosilane (DMDCS; by weight). Constant-head ponding was applied on the soil surface. The test results revealed that the hydrophobized barrier could prevent the underlying soil from an increase in water content as long as the ponding head was less than the water-entry head (WEH) of the barrier. The barrier could become ineffective to prevent percolation when the mass portion of the hydrophobized sand was reduced or when the initial degree of saturation increased because of the reduction of WEH.