Influence of geomembrane on the deformation behaviour of clay-based landfill covers

Clay-based landfill covers often have a geomembrane (GM) layer sandwiching between the clay barrier and the cover soil. The knowledge pertaining to the deformation behaviour of a clay barrier along with geomembrane subjected to differential settlements is very limited. Hence, the main objective of this paper is to examine the influence of GM on the integrity of clay-based landfill covers subjected to differential settlements in a geotechnical centrifuge. First, scaling considerations required for modelling geomembrane in a centrifuge are presented. A series of centrifuge tests were performed at 40 gravities using a 4.5 m radius beam centrifuge having a capacity of 2500 g-kN available at IIT Bombay on model clay-based landfill covers with and without GM. By maintaining type moist-compacted conditions of the clay barrier as constant, the thickness of the clay barrier was varied as 0.6 m and 1 m. The performance of the clay barrier with and without GM was monitored by measuring water breakthrough at the onset of differential settlements. The analysis and interpretation of centrifuge test results reveal that with the provision of a GM and an overburden pressure equivalent to that of a landfill cover, the sealing efficiency of the cover system was found to be maintained even after the formation of full-depth cracks within 0.6 m and 1 m thick clay barriers subjected to a maximum distortion level of 0.125. This observed behaviour is attributed to the downward thrust exerted by the deformed geomembrane at the zone of maximum curvature which hinders the infiltration of water through cracks. This indicates the significant influence of GM in maintaining the sealing efficiency of a landfill cover system.