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Abstract
Landfills are different to dumps or tips, which are what most peope
think of when they hear about landfills, because tbey 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 tbe surrounding environment, particularly groundwater.
Traditionally, these liner systems are composite of compacted clayey soil
and a synthetic membrane. However, 10 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 HQPE 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 1O-7crn/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 landfi II 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, owdered forms, are much easier to blend with onsite sandy soils and to be
compacted than wet, sticky clods of clay.
The central part of the experimental program focused on the detailed
investigation of the permeability coefficient of the sand-bentonite mixtures.
The factors affecting it such as the bentonite content and the vertical stress
are studied. The impact of real municipal solid waste leachate on the Liner
permeability is also investigated.
Volume change after inundation IS also investigated taking into
consideration the effect of the bentonite content and the type of the
permeating fluid
The results are presented and analyzed. These results are
implemented to elaborate a frame work to the liner design procedure.
Recommendations for future researches are made.
Keywords: MSW Landfills, Sand-bentonite mixtures, Natural Clay liner,
Geomembrane, MSW Leachate, Coefficient of Permeability, Composite Liner.-