Patrick Selvadurai

Abstract:

Polyvinyl chloride (PVC) membranes are used in geoenvironmental endeavours to prevent groundwater contamination due to leakage of leachates from landfill and other hazardous waste sites. PVC membranes constitute an important component of multi-barrier containment systems that also include layers of impermeable clay and PVC leachate collection systems. Geosynthetic membranes used as landfill liners can be exposed to adverse environments, including heat, exposure to ultra-violet light during construction, bacteria, and chemicals [1]. Despite their widespread use, their long-term effectiveness under exposure to chemicals, such as ultra-violet light, radiation, etc., are poorly understood. A primary requirement of a geosynthetic membrane relates to its ability to undergo large deformations and maintain its integrity, thereby impeding the migration of hazardous chemicals and contaminants to the environment. Experiments conducted in connection with this research indicate that the interaction of the geosynthetics with chemicals such as acetone and ethanol leads to loss of plasticizers that are necessary to maintain the hyperelasticity of geosynthetics [2, 3]. The longevity of the containment provided by PVC geosynthetics can be influenced by these factors, specifically in situations involving the thermal desiccation of clay. Desiccation cracking can be caused by moisture depletion in the clay barrier following exothermic processes associated with the decay of organic matter in a landfill. A cracked clay barrier provides a pathway for contaminants to come into direct contact with a geosynthetic barrier.
In contrast to rubber-like elastic materials [4-7], glassy polymeric materials exhibit appreciable irreversible effects, including development of permanent strains during loading-unloading cycles and strain-rate effects. This paper presents constitutive models that first describe the hyperelastic behaviour of a geosynthetic material in its untreated condition. The modelling accounts for both reversible and irreversible components of hyperelastic behaviour and incorporates strain-rate dependency in the constitutive response. The constitutive modelling is then extended to include the long-term loss of hyperelasticity because of exposure to pure ethanol. The constitutive parameters were determined from uniaxial tests and constrained tests conducted at different strain rates. The constitutive models were implemented in a general-purpose finite element code to examine the mechanics of a membrane fixed along a circular boundary and loaded by a hemi-spherical indenter. The comparison between the experimental results and the computational estimates were used for the purposes of validating the modelling approach.

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