A new cell at the McRobies Gully landfill required a lining system that could handle Hobart's 600 mm annual rainfall and the steep slopes of the site. The engineering team needed a geomembrane specification that addressed both the chemical composition of the leachate and the differential settlement expected over the underlying waste mass. We developed a 1.5 mm HDPE textured geomembrane spec, referencing GRI-GM13 for tensile properties and AS 3706.3 for seam strength. The specification included a dual-track wedge welding protocol and pressure testing at 200 kPa. This level of detail prevents liner failure before it starts. For sites with variable subgrade conditions, we often combine the geomembrane spec with a geotextile cushion layer assessment to prevent puncture, and verify the bearing capacity through plate load testing on the prepared surface.
A textured geomembrane on a 2H:1V slope in Hobart requires a minimum interface friction angle of 18 degrees to prevent sliding failure.
Methodology and scope
- Thickness: 1.0 mm to 2.0 mm depending on exposure and chemical resistance needs
- Seam strength: minimum 80% of parent material shear strength per AS 1289.5.7.1
- UV resistance: minimum 500 hours of accelerated weathering per AS 1289
Local considerations
The difference between a lining project in Sandy Bay and one in Glenorchy is stark. Sandy Bay's dolerite-derived soils offer a stable, well-draining subgrade with low settlement potential. Glenorchy's sites near the Derwent often sit on deep alluvial silts and estuarine clays. A geomembrane specification that works on the former can fail catastrophically on the latter. The risk is differential settlement creating a ponding effect that overstresses the seams. In Hobart, we always require a subgrade modulus of at least 30 MPa/m, verified by a plate load test on a 600 mm grid. Without it, a 2.0 mm HDPE liner can experience localized strains exceeding 5% in the first year alone.
Applicable standards
GRI-GM13 (Geomembrane Standard Specification), AS 1289 (UV Resistance Testing), AS 3706.3 (Geotextiles - Seam Strength), AS 1289.5.7.1 (Seam Shear and Peel Testing)
Associated technical services
Landfill Liner Specification
We define the complete barrier system for municipal and industrial waste cells in Hobart. This includes selecting the geomembrane thickness (typically 1.5 mm to 2.0 mm HDPE), specifying the geotextile cushion, and writing the seam testing protocol per AS 1289.5.7.1. We also review the leachate chemistry to ensure chemical resistance.
Pond and Reservoir Lining Design
For water storage and evaporation ponds in Hobart's agricultural and mining sectors, we specify geomembranes that resist UV exposure and thermal cycling. Our design includes anchor trench details, ballast calculations, and a leak detection system specification. We reference GRI-GM13 and AS 3706.3 to ensure long-term performance.
Typical parameters
Frequently asked questions
What is the difference between a smooth and textured geomembrane specification for Hobart's terrain?
A smooth geomembrane has a low coefficient of friction and is only suitable for flat areas or where a geotextile interface is used. A textured geomembrane, with asperities of at least 0.25 mm height, provides the interface friction needed for slopes steeper than 3H:1V. In Hobart's Derwent valley sites with silty subgrades, textured liners are the standard for slopes exceeding 10 degrees.
How much does a geomembrane specification service cost in Hobart?
The typical cost for a full geomembrane specification package including material selection, installation QA/QC plan, and subgrade assessment ranges from AU$1,050 to AU$2,510. This depends on the site area, number of liner zones, and complexity of the leachate or water chemistry. A basic specification for a small pond starts around AU$1,050.
What testing is required to verify a geomembrane installation in Hobart?
We require destructive seam testing per AS 1289.5.7.1 (shear and peel) at a frequency of one test per 150 m of seam. Non-destructive testing via vacuum box or spark testing is performed on 100% of seams. The subgrade must pass a plate load test to confirm a modulus of at least 30 MPa/m. The geomembrane itself must have a certified carbon black content of 2.0-3.0% per AS 1289.
How long does a geomembrane lining system last in Tasmania's climate?
With a proper specification including UV-stabilized HDPE (minimum 2% carbon black) and adequate cover, a geomembrane liner in Hobart can last 20 to 30 years. The key factors are UV exposure, chemical resistance to the contained material, and protection from subgrade puncture. We specify a 1.5 mm minimum thickness for uncovered applications and require a geotextile cushion where the subgrade has angular particles.