Simulating Water Balance of Road Embankment Lysimeters

Abstract

An alternative to dumping mineral materials containing moderate amounts of contaminants into landfills is to reuse them in road embankments and noise protection barriers. To ensure groundwater protection, seepage of precipitation water through these materials must be omitted or reduced to a minimum. Embankments consisting of both cohesive and coarse-grained soil materials under various designs of cover layers were investigated within six field lysimeters. To gain the understanding of the water balance, quantities of seepage water, as well as runoff in the cover layers and on the surface were monitored. When using moderately contaminated materials in earthworks, reliable prediction of the water balance is crucial. Thus, in this study 2.5 years of the lysimeter experiments were modeled using the finite element software Vadose/W. Results were compared to the experimental data. The unsaturated hydraulic characteristics of the core materials were known from experimental investigations. Those of the topsoil and the shoulder material were estimated from databases of similar soils. A climate boundary condition represented the daily mean of the actual climate data on-site including road runoff. The modeled water balances were in good agreement with the field data for the cohesive core material of low permeability. However, a tendency to overestimate of seepage water was observed, which was even higher in the lysimeters with coarse-grained materials. This is linked to the water-permeability of the shoulder material and demonstrates that the cover layers have a major influence on the water balance of the whole embankment.