Experimental Acceptance Procedure for Using Cullet in the Gas Collection Layer of MSW Landfill

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.