Whytes Gully New Landfill Cell Construction
Wollongong City Council owns and operates Whytes Gully Resource Recovery Park, which currently receives all of the municipal solid waste within the Wollongong local government area. With existing landfill airspace at Whytes Gully Resource Recovery Park projected to expire in late 2013, Wollongong City Council proposed the construction of several new landfill cells on the occupied site, on top of and adjacent to existing landfill locations. Once completed, the 4 stages of the project would extend the capacity of the Whytes Gully site by a further 6 million m³.
Select Civil engaged in a $10.5 million contract with designer and superintendent Golder & Associates to construct the first stage of the new landfill cell construction; packages 1A and 1B, both piggyback cells built directly above compacted, putrescible waste.
The high specification cell construction consisted of coalwash and clay earthworks, polymer liner placement and welding, geosynthetics deployment, subgrade and surface pipe installation, gravel placement and surface drainage works.
The project also consisted of ancillary works including the construction of 3 asphalt roads, diversion drains, gabion drainage structures, culvert installation, subgrade gas pipe network installation, minor earthworks and buildings demolition.
The installation of subgrade perforated gas pipework involved trenching and backfilling with nominated single-size aggregate beneath the compacted clay liner and synthetic works. The subgrade gas pipework is crucial to the success of the landfill cell, collecting any generated methane or other gas from existing waste below the liner, preventing build-ups creating unstable surfaces, and possible explosions. Collected gas was redirected to an onsite flare for ignition, and potential future use as an energy source.
Due to the piggyback and unstable subgrade nature of the project, special consideration needed to be adopted during design and construction of the synthetic lining portion of the works. The synthetic liner consisted of a geocomposite clay liner, low/high density polyethylene plastic liner and bi-planar geocomposite drainage net. Plastic lining weld seams were rigorously tested to project specifications, with only a small portion not achieving strength or air pressure requirements and demanding repairs or replacement. The synthetic lining works covered an area of over 50,000 m².
A major component of the secondary works scope of the Whytes Gully project was the construction of the Western Gully Haul Road, a 470m asphalt road construction on an existing waste cell. The finished road would link existing routes with the active tip face, and provide access for the operations team to meet requirements of the sites EPA approved fill plan.
The finished product was line marked, signposted and finished with trie-beam barrier rail to the requirements and satisfaction of the client.