Abstract
The multilayer system of a non-hazardous solid wastes landfill cover, required by most international regulations, includes a granular layer of adequate permeability and thickness for the collection and drainage of biogas. The choice of the most suitable material generally falls on granular soils, containing very low percentages of fines. The paper presents the possibility of replacing natural soils with cullet, obtained by the glass shredding, and widely available on the market. Its hydraulic conductivity with regard to biogas and its granulometric compatibility with the adjacent layers may be initially assessed by means of the usual filter design criteria. Then, its crushing strength, under static and cyclical loads, must be evaluated, since the capping systems are crossed by heavy earthmoving trucks, and consequently, there is the possibility of a change of the cullet granulometric distribution. As cullet is not a conventional material, the usual geotechnical laboratory tests cannot be directly applied to it. The paper suggests an innovative laboratory procedure, defined as a static and cyclical punching test, which allows to evaluate the crushing resistance of cullet by using the traditional apparatus for soil compaction.
Highlights
As regards the cover of non-hazardous municipal solid waste (MSW) landfills, the European Council Directive 1999/31/CE [1] imposes a biogas collection layer (BCL) thickness not less than 0.5 m and requires an adequate protection from clogging
The granular material composing of BCL firstly has to satisfy the following retention and permeability criteria: (1) a grain size compatibility with adjacent layers must be achieved on the basis of the usual filter design criteria; (2) the internal self-stability (ISS) of the layer must be guaranteed through the absence of cementing minerals and elongated grains and avoiding the migration of the finer particles; (3) the BCL must bear stresses induced by dynamic and static loads acting during the different phases of its life
After cyclic static punching (CSP) tests, the GSD curves of tested representative portions evolve as a consequence of particle breakage phenomena occurring during loading (Fig. 6a–d)
Summary
As regards the cover of non-hazardous municipal solid waste (MSW) landfills, the European Council Directive 1999/31/CE [1] imposes a biogas collection layer (BCL) thickness not less than 0.5 m and requires an adequate protection from clogging. This allows to avoid a geotechnical instability of capping, induced by the build-up of the biogas pressure below the mineral liner. The finer fraction increases and the average hydraulic conductivity of BCL decreases; this could make the granular material no more suitable for the design purpose. The above-mentioned Council Directive does not prescribe in detail the materials to be employed in the BCL of a non-hazardous MSW landfill
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