Sealing the Slope: Rochedale Landfill’s Capping Project
The Project
Spanning 4.7 hectares across Cells 6B, 7, and 8, the western slope of Brisbane Landfill in Rochedale, reached capacity in 2026, necessitating a capping project to contain landfill gas in line with Queensland EPA DETSI requirements.
Capping landfills protects groundwater from contamination and prevents methane from escaping into the surrounding environment, making it an essential component of responsible waste management. For the western slope capping project, waste management and resource recovery company Cleanaway Solid Waste Pty Ltdy was engaged to deliver the works. Global Synthetics was proud to also be engaged as a supplier for this project.
The Challenge
The landfill would still be active during the capping process, with gas extraction infrastructure across the site operating. Therefore, health and safety had to be front of mind throughout construction. Adding to this, the waste beneath the cap was still fresh, so ongoing settlement of both the waste and the capping system had to be considered in the approach.
The Solution
The solution presented was to build a total capping solution from a combination of geosynthetics, with the installation works split into four separate sections, each needing its own sequencing and staging. Each section would be constructed separately as to maintain gas infrastructure throughout, with pipe disconnection, sealing, and reconnection.
To help speed up construction, Naue Bentofix® X10F NSP4900 Coated GCL was used for the barrier layer. This Geosynthetic Clay Liner (GCL) has a thick, 1mm surface polyethylene coating, which increases the pull-out resistance as well as the internal shear strength. This negated the need for a separate LLDPE geomembrane, avoiding a two-layer system which could have posed a risk of interface slippage between layers. In addition, the use of a GCL reduced the layers of fill required to perform the confining layer.
A geonet composite was installed above the GCL layer to manage surface water, controlling run off and preventing the risk of ponding that could cause undue strain on the system.
As a final element of capping, the western slope surface had to be covered in a veneer of cover soil and then resurfaced with turf. To support the stability of the cover soil over the steep slopes, AceGrid® Uniaxial Geogrid was installed. ACEGrid® is an engineered woven geogrid that has exceptionally high strength characteristics at low levels of strain, for long term soil reinforcement. This will ensure the ground stays covered, protected, and will support the new vegetation growth.
Around the perimeter of the cap, at the halfway bench and along the base, Global Synthetics Link® Rock Mattresses were also utilised to capture water discharged from the geonet, and to direct surface water run-off to controlled discharge points. Link® Mattresses provide a highly versatile solution of earth retention and erosion protection.
Their flexible and porous nature allows them to provide high flow and shear resistance to scour, which is essential to reduce erosion risks.
The Result
Installed as a complete system, this entire solution was quick and efficient to construct, delivering cost savings while maintaining worker safety from gas exposure and safeguarding the surrounding environment.
The Bentofix coated GCL’s high shear strength eliminated the need for a separate geotextile layer, simplifying installation on fresh, still-settling waste. On an active site where staged sequencing and gas infrastructure reconnection were required throughout, this efficiency was critical to keeping the works on programme and cost-effective.
To ensure long-term performance, AceGrid® reinforced the cover soil on the steep slopes to support long-term vegetation growth, while the Link® Rock Mattresses deliver durable, low-maintenance erosion protection along the cap’s perimeter and benches, safeguarding the system’s long-term integrity against surface water discharge.
Need help with your next landfill capping or environmental containment project? Contact Global Synthetics today.
