Landfills, when decommissioned / closed, shall be encapsulated / capped by a combination of drainage systems and contamination barriers to minimise adverse effects on the environment to an ac-ceptable level. Capping systems should permanently restrict the uncontrolled release of landfill gas and leachate, as well as the infiltration of precipitation into the waste by effective management of the storm-water runoff from the capped surface of the final landform.
The core elements of the sealing systems were earthen components such as clay as the classic sealing layer and gravel / sand as the drainage layer for water / leachate and gas. These have been known as ‘earthen capping’ solutions. The earthen components shall be compliant with the installation criteria and constructed to a high standard; however, their long-term effectiveness is often susceptible to factors such as: desiccation cracking, erosion, differential settlement, displacements (especially on slopes and above compressible waste), material availability, interface shear strength, and construction quality control. To overcome some of these issues, various geosynthetic materials have also been developed and utilised in landfill sealing and drainage systems, commonly known as ‘Geosynthetic’ capping solutions.
In this paper, an innovative engineering approach to select a landfill capping profile has been introduced which utilises the concept of multi-criteria assessment for the capping profile alternatives considering the international standards, Australian landfill design guidelines, local factors and site specific parameters that affect the short-term and long-term performance of the final landform.
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