Study of the hydric behaviour of double-layered columns of unsaturated soils - Analysis of water and suction profiles during infiltration tests

Abstract

Systems of sealing of containers or retention pounds are often associated to drainage layers for leachate recovery. The drainage layer can be installed either above the sealing layer or below it. In this paper, double layered columns of alluvia and clayey sand or of alluvia and clay are made up to run infiltration tests. A follow-up of the water content is implemented during the infiltration in multi-layer columns by using TDR probes. The values and changes in infiltration rate are different if the drainage layer is above or below the sealing layer. It is found that the drainage layer saturation is delayed when the sealing layer is above but the equilibrium water content remains the same for the both configuration. The electrical measurements in the drainage layers prove that the increase rate of the solute accumulation is the same for the both configuration and the same equilibrium solute concentration is reached. The measured coefficient of permeability of the double-layered becomes five times higher when the drainage layer is below the sealing layer. The position of the drainage layer influences the infiltration rate, the water and solute migration. The change in coefficient of permeability must be taken into account for the assessment of the flux of pollutant across a barrier system.