Magnitude and significance of tensile strains in geomembrane landfill liners

The implications of the tensile stress/strain developed in high density polyethylene (HDPE) geomembranes (GMB) is explored in the context of a reduction in stress crack resistance due to ageing in contact with leachate in a municipal solid waste (MSW) landfill. The experimental evidence of GMB cracking and ultimately failure when subject to excessive tensile strains is discussed to highlight the need to limit the maximum tensile strain sustained by an HDPE GMB to an acceptable level if good long-term performance is to be ensured. The effect of both local GMB indentations induced by gravel in an overlying drainage layer or an underlying clay liner on tensile strain is reviewed. In addition, the tensile strains caused by down-drag in the GMB on side slopes with settlement of the waste is examined. The key research related to tensile strains developed in GMBs from these sources is reviewed and new data presented. It is shown that an appropriate protection layer over the GMB can limit local GMB tensile strains to less than 3% and that the selection of a suitable slope inclination and stiffness of a geotextile reinforcement layer can limit the GMB strains due to down-drag to less than 2% and geotextile strains to less than 4% after long-term waste settlement.