Effects of Temperature on the Service-Life of Landfill Liners and Potential Temperature Control Strategies
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Landfill facilities are required to have a barrier system that will limit escape of contaminants to groundwater and surface water for the contaminating lifespan of landfill. Heat generated by the biodegradation of waste and chemical reactions in landfills reduces the service-life of geomembranes by accelerating the ageing process of high-density polyethylene. It may also lead to the desiccation of clay components of the liners. Four considerations with respect to the evaluation of the potential effects of liner temperature on the service-life of liners and the potential control of liner temperature are examined. For the first time, the likely temperature and service-life of a secondary geomembrane in a double composite lining system is predicted. It is shown that, in some cases, the temperature is likely to be high enough to substantially reduce the service-life of the secondary geomembrane. The possible effectiveness of using tire chips as passive thermal insulation between the primary and secondary liners, as well as traditional soil materials, is then explored. For the barrier system and contaminant examined, the results show that tire chips could potentially lower the temperature of the secondary geomembrane sufficiently to significantly extend its service-life. However, the use of tire chips brings about other practical issues, which are also discussed in this study. An active alternative method of controlling the increase in the landfill liner temperature is then examined. This approach, which is inspired by geothermal heat pumps, involves an array of cooling pipes beneath the waste. Numerical modelling showed that the hypotetical introduction of the cooling pipes resulted in a reasonable decrease in liner temperature. It is suggested that the proposed technique warrants further consideration. Finally the conditions that may lead to the desiccation of geosynthetic clay liners used in composite liners due to waste generated heat are examined and recommendations regarding possible means of mitigating the effects of heat on the performance of GCLs are presented. For example, numerical modelling shows that the hydration of GCL prior to waste placement, liner temperature, overburden stress, depth to aquifer and moisture content and grain size of subsoil affect desiccation.