Landfill Treatment For Westlink M7

Westlink M7 is one of Australia’s largest urban road projects and was a key missing link in Sydney’s orbital road network of motorways. A section of an onload/offload ramp of an interchange was constructed over an existing landfill comprising municipal solid waste with a depth up to 12-13 m. To control settlement of the road built over the landfill, a series of stone columns were installed in the landfill, known as dynamic compaction (DC) and dynamic replacement (DR). The stone columns were extended to about 5-6 m depth founding on compacted waste material. Due to the complex composition and variability of the waste material, it is difficult to predict the long-term performance of the landfill. Worldwide research in this area has continued for 30-40 years and some information has become available for the design of landfill treatment. Detailed 3-dimensional numerical modelling was carried out to simulate the expected settlement of the landfill and predict the impact of this settlement on the pavement. In situ tests were carried out in the landfill before and after the DC/DR treatment to demonstrate improvement of the landfill property. The treated landfill was also preloaded for a period of time and settlement monitored to confirm the effect of the treatment.