Leakage Through Clay Liners (Groundwater, Landfills, Soils).

Precipitation which enters a solid or hazardous waste landfill is a potential source of groundwater contamination. A cover liner is typically constructed over a completed waste landfill in an attempt to reduce the potential contamination. All too often, the design of such liners relies on critical simplifying assumptions rather than a sound theoretical and empirical base. The present investigation considers both the theoretical and experimental aspects of flow through clay liners. A sample of the clay soil used as a liner material at a field installation was procurred and subject to a series of experimental tests to characterize its unsaturated material properties. A numerical model was developed to simulate the variably saturated conditions of a three layered system: s and drain, clay liner and refuse material. The model was used to simulate the field conditions over a four year period for which precipitation information was available. The modeled leakage consistently underpredicted the observed field condition, suggesting the possible inadequacy of the laboratory investigations in field applications. The numerical model was applied to a more general l and fill liner problem, which includes lateral drainage in a slightly sloping cover layer of permeable soil. A series of model simulations were performed to assess the variations in leakage corresponding to different liner designs and liner material specifications. The refuse material properties were investigated to a lesser degree. Several climatic conditions were simulated to evaluate the nature of the relationship between precipitation and subsequent leakage. The temporal distribution of the precipitation was as critical to the leakage solution as the total volume of precipitation, indicating that simulations based on the average annual rainfall may not be sufficient. The contributions of the dissertation are two-fold. The limited data base for experimental investigations of unsaturated clay soils is enhanced. The inclusion of the unsaturated material characteristics in a numerical model of the liner problem has presented a more realistic approach to the calculation of leakage.PhDCivil engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/160385/1/8502892.pd