Operated by Hanson, Wollert Landfill is a Waste Management Association of Australia (WMAA) Gold Excellence Award winning landfill. Since its opening in 2000, Wollert Landfill has been providing the safe disposal of waste for households, as well as commercial, industrial and demolition businesses across the state of Victoria. The landfill is constructed in cells that hold about 500,000 tonnes of waste and take 18 months to fill. Golder Associates were approached to design a cost effective final capping system to meet the high environmental standards operated by the site.
The filled landfill cell needed to be safely capped with a permanent cover system which prevented the infiltration of water and the escape of gas which is converted to electricity. The proposed final capping comprised a three layered geosynthetic, permanent capping treatment: a geosynthetic clay liner (GCL), a 1.5 mm LLDPE liner and a geocomposite drainage layer. A suitable geocomposite was required to provide adequate drainage underneath the 1m non-descript crush rock (NDCR) overburden.
Designer Golder Associates established that the pressure of the NDCR overburden would necessitate the selection of a suitable geocomposite. Working with ABG, it was determined that in-plane water flow values from tests obtained using soft foam platens should be used in the calculation of the required drainage (see diagram below).
Site simulation testing showing the superior void spanning ability of ABG Pozidrain over a typical geonet core drainage composite
Testing with soft foam platens simulated the soil overburden and the resulting intrusion of the geotextile into the drainage core under a given pressure. Pozidrain 7S250/NW8 was chosen to meet the necessary water flow. In addition to the benefit of a more competent flow, Pozidrain with one geotextile and a virtually impermeable core, provides a cost saving compared to a geonet with two textiles. Pozidrain’s unique drainage core also served to provide the lining system with an additional measure of protection. Pozidrain was delivered to site and successfully passed the rigorous conformance testing.
The ABG Service
ABG provided flow testing and design advice from chartered civil engineers, drawing on over 25 years of landfill experience.
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