Design and construction of a compacted clay liner in the cover system of a MSW landfill using not standard procedures

Design and construction of a mineral barrier layer involve many experimental and technological aspects. A specific soil water content and laboratory compaction energy, which are required to obtain permeability values according to the national regulation in force, must be determined. It is also necessary to control water content, compaction energy, and permeability of the liner actually compacted in situ. This paper shows how a compacted mineral barrier mainly composed of silty clay soil (the excavated soil is a natural but potentially re-usable waste product) was put in place to cover a large municipal solid waste (MSW) landfill and compacted using a heavy dumper, capable of achieving an adequate compaction degree. The in situ hydraulic properties of the liner were compared with those obtained by laboratory testing and to the limits imposed by the Italian regulation. The actual compaction degree was checked by in situ tests. Hydraulic conductivity tests were carried out in situ, using Boutwell and Guelph permeameters, and in the laboratory using rigid wall and flexible wall permeameters. In situ testing provided more realistic permeability values than laboratory ones and demonstrated that the actual construction procedure used was effective to obtain the design targets.