PERFORMANCE OF PROTECTIVE COVER SYSTEMS FOR LANDFILL GEOMEMBRANE LINERS UNDER LONG-TERM MSW LOADING

This paper presents the results of large-scale laboratory simulation t ests conducted to evaluate the relative performance of different cover systems, consisting of a granular soil layer (i.e. a drainage layer) both with and without the presence of a needle-punched nonwoven geotex tile, to protect a 1.5 mm thick smooth HDPE geomembrane liner under lo ng-term municipal solid waste (MSW) loading conditions. Five different granular soils that range from a coarse gravel to a medium sand were used in the testing program. The protective cover system and the geome mbrane liner were subjected to incremental loading to a maximum pressu re of 1.4 MPa. The effect of long-term loading on the characteristics of the cover soils was assessed by performing particle size analyses, and the physical damage that occurred to the geomembrane liner was vis ually assessed in addition to performing multi-axial tension, wide str ip tension, and water vapor transmission tests. The test results revea led that the degree of geomembrane liner protection decreases as the s oil mean particle size increases and as the soil particle sphericity d ecreases. This study demonstrates that a 300 mm thick granular soil la yer consisting of particles with a mean size less than 30 mm and a sph ericity greater than 0.8, combined with a 270 g/m(2) nonwoven geotexti le provides adequate protection for a 1.5 mm thick HDPE geomembrane li ner from MSW loading.