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Abstract
Landfills are different to dumps or tips, which are what most people
think of when they hear about landfills, because they are carefully
constructed with special lining and covering systems to contain the waste.
The aim is to avoid any hydraulic [water-related] connection between the
wastes and the surrounding environment, particularly groundwater.
Traditionally, these liner systems are composite of compacted clayey soil
and a synthetic membrane. However, In Egypt most of the engineered
landfills are having a single liner system consisting from geomembrane
(HDPE) sheets. For that purpose, part of this study investigates the effect of
imperfections of the HDPE sheets on the overall permeability of the
composite liner to emphasize the importance of the secondary liner in the
prevention of the ground water table contamination.
Engineering specifications for a compacted clay liner are based
mainly in a permeability coefficient less than 10-7cm/s and the need for
stability during construction and operation of the landfill.
Sand-bentonite mixtures are often used as a barrier material when
there is a lack of naturally occurring clayey soils at the landfill site. The
addition of relatively small amounts of bentonite (5-15%) can improve the
performance of a granular material providing both a low permeability and
an enhanced mechanical stability. In addition, bentonites, obtained in dry,