Innovative Aspects in Landfill Design
Abstract
A solid waste landfill facility is being developed within an existing limestone quarry, located approximately 4 kms east of Winton in Southland, New Zealand. Sinclair Knight Merz (SKM) has been involved in the consenting, design of the landfill and project management of the construction of the landfill. This paper describes the innovative design approach adopted to address various environmental and geotechnical issues associated with the development of the landfill.
The quarry floor and part of the sidewalls are in karst limestone with inflow and outflow features. The landfill base and sidewall liners were designed to dissipatete artesian pressures from outflow features by designing suitable drainage layers. The underdrainage for the concrete Leachate tank was designed to maintain a minimum head of water to retard any potential leaks from the tank through cracks in the concrete. Under normal landfill operating conditions, the inflow gradient into the tank was greater than the outflow head. Testing of locally available residual clays indicated abnormal index properties and moisture contents. Petrographic analysis and further tests indicated the presence of pockets of calcium smectites and chlorites in the clay. The earthworks specification and clay liner design was specifically aimed at addressing this issue during construction. An unique design was adopted for the leachate collection layer by using coarse rounded gravel with a layer of biaxial geogrid on top to provide confinement during placing of subsequent layers above. This design was aimed at increasing the life of the leachate collection layer and to address problems caused by the formation of biofilms.