Backfilled Quarry Development with Inbuilt Landfill Gas Solution

Backfilled Quarry Development with Inbuilt Landfill Gas SolutionA basalt quarry north east of Melbourne operated for over 30 years from the mid-1960s. Rock extraction occurred to a depth of approximately 28 m below ground level with dewatering. Since operations ceased in 1999, the quarry has been progressively backfilled with variably compacted ‘clean fill’ until 2017 and the groundwater level allowed to rebound close to its former level. Potential development of the land, for residential or mixed land use, triggered geotechnical and environmental investigations with the objective of identifying and managing below ground issues to support a planning rezoning process. Based on the investigation results, some of the key considerations for future development of the site were settlement of the backfilled quarry, foundation system options across the filled quarry extent and management of landfill gas. Development time, future ongoing management pressures and the need for large scale ground improvement, led to the consideration of a landfill gas control barrier integrated within the engineered fill ground solution, and an on-site trial. This paper provides the findings from the surcharge trial to date to combine the reduction in time to achieve an acceptable settlement of the fill and the management of entrapped landfill gas.