Water Balance of an Earth Fill Built of Compacted Clay: Field Data and Numerical Modeling

Abstract

With the aim of testing an alternative sealing system for noise protection embankments containing environmentally hazardous substances, a fill of compacted clay with organic and elevated arsenic content was tipped. The fill was extensively monitored to measure the water balance and seepage. Due to the low permeability of the soil, a simple capping, consisting of a geosynthetic drainage mat and a clayey top layer, was used. Measurements over a 10-year period demonstrate that the chosen capping system is very efficient in minimizing seepage from the core. The success is based on a high water retention capacity of the topsoil in combination with the capillary-breaking effect of the drainage mat. Numerical simulations of the water balance of the test fill indicated that the calculation results are very sensitive to the fineness of the finite-element mesh, the choice of the time steps, and the hydraulic properties of the drainage mat. After calibrating the hydraulic properties of the drainage mat using the measured data of the first 3 years, the measured water balance of the 10-year period could be reasonably predicted by the model. Differences between the measured and the calculated discharges from the drainage mat and the core material are attributed to heterogeneities of the materials in the field and to the hysteresis of the soil water retention curve not being considered in the model.