Assessment of alternative protection layers for a geomembrane - geosynthetic clay liner (GM-GCL) composite liner

A protection layer is required above geomembrane (GM)-geosynthetic clay liner (GCL) landfill liners to limit physical damage (GM strains and GCL thinning) from an overlying granular drainage layer. A 150 mm thick layer of sand has been found to provide excellent protection at a vertical pressure of 250 kPa. However, the use of sand may not be practical in many cases. Experimental results are presented where the effectiveness of alternate protection systems above one particular GM-GCL liner were examined with 50 mm coarse gravel at an applied vertical pressure of 250 kPa. A 150 mm thick layer of compacted clay and a 150 mm thick layer of rubber tire shreds with a nonwoven needle-punched geotextile (570 g/m(2)) were found to limit the geomembrane strains and GCL extrusion to acceptable levels. Layered geotextiles performed much better than single layers of geotextiles. A layered geocomposite, with a thick nonwoven needle-punched geotextile in the middle to provide cushioning and stiffer woven geotextiles on the top and bottom to carry tensile force, was able to limit the short term strain to less than 3%, but it was not able to prevent local thinning of the GCL because of the deformation required to mobilize force in the geotextiles.