A regional renewable energy project had to be completed on a tight timeframe with minimal environmental impact. Partnering with geogrid manufacturer Tensar® helped the project’s team take on the challenge.
Under construction in the central west of New South Wales, 14 km from Wellington, is a new 69-turbine wind farm that will produce enough electricity to power 220,000 homes and allow the region to forgo more than 560,000 t of carbon emissions annually.
The Uungula Wind Farm project extends across 8500 ha of undulating terrain. Erecting the turbines requires energy infrastructure contractor NACAP to move 2.5 million cubic metres of material ranging from hard granite to low-quality soil, as well as construct 76 km of internal tracks through the site.
Just facilitating site access in this environment presents its own challenges. Stabilising the low-quality soil in the subgrade – the layer of material immediately below the road construction – would involve a mechanical or chemical approach that would provide an alternative to excavating and replacing the soil.
That would create its own problems, since material removed during construction must be taken away from the site. Meanwhile, wind farms such as this one required very large mobile cranes to be delivered and operated, all with reduced clearing limits, and development is confined to a small corridor.
“We’re following the environmental impact studies and the regulation from the Department of Primary Industries, and there are certain species of native vegetation that we’re not able to disturb, all of which keeps us within a narrow footprint,” said NACAP Project Manager Scott Sartori.
“So we have to be very mindful that, when we excavate material to find a stable substrate, that material has to go somewhere. The issue that we’re faced with, particularly in these types of developments, is that we simply don’t have anywhere for that material to go.”
Adding to Sartori’s challenge were the tight time pressures involved. Although NACAP’s original approach to constructing access roads on the site would have involved an excavate-and-replace process, followed by a chemical solution such as lime stabilisation, arranging for contractors to come in and do the work would have delayed the project excessively.
The lime would also have been potentially hazardous to the local environment, and sourcing the required materials for it would have introduced further project delays. Getting the lime to the site would have imposed a heavier traffic burden on the local community too, as trucks would need to run back and forward making deliveries.
“Reducing traffic and reducing the impact on the community is an important factor and is going to become a more prominent concern in the industry as time goes on,” Sartori said.
“Adopting a single layer solution while avoiding chemicals is very important for a green renewable project like this. It matters for these programs that we can get in and out of the community when we say we will.”
Partnering with the professionals
Sartori reached out to Petro Flokis, Regional Sales Manager NSW/ACT at Tensar, a division of CMC with his challenge. Tensar, a manufacturer and solution provider for geogrid applications, have more than 40 years’ experience working in the global market. Tensar provided technical input and trial support to help NACAP validate a mechanical stabilisation option early, before the road build scaled up.
By involving Tensar early in the development of the Uungula project, Sartori could draw upon the company’s engineering expertise and engage it as an extension of his project team.
“You can’t wait around for alternatives, which is why it was important to get the test trials done early in the process to satisfy the requirements and the construction schedule and to measure the environmental impact.”
Tensar’s proposed solution was its Tensar InterAx Geogrid product, a stabilisation geogrid used to improve the performance of granular layers over weaker subgrades by promoting aggregate interlock and confinement – reducing deformation under wheel loads and forming a mechanically stabilised layer.
In areas of low-quality subgrade, stabilised designs can significantly reduce the thickness of imported aggregate, which can mean fewer truck movements, lower cost and lower embodied carbon. Tensar says aggregate reductions of up to 70 per cent and carbon reductions of up to 65 per cent are achievable in some applications.
“Tensar InterAx Geogrid is our next-generation stabilisation geogrid,” said John Buckley, Area Engineer Manager ANZ at Tensar International.
Tensar InterAx Geogrid offers a high level of confinement for aggregate, resisting lateral spread under vertically applied wheel loads. That mechanically stabilised layer increases strength and stiffness compared to a non-stabilised aggregate.
During the testing phase, Sartori showed that the material was suitable for construction on the low-quality soil, and by being able to reduce the material that needed to be removed from the site, it accordingly reduced traffic, benefiting the environment and the local community.
While similar projects will often see unsuitable soil to a depth of 1.2 m removed, the mechanical approach offered by Tensar InterAx Geogrid meant Sartori would only have to go to a depth of 300 mm before laying down the geogrid material and introducing the substrate.
“It’s a much faster process,” Sartori said.
“The teams learn quickly how to get this material down, push on and then keep going. All this plant doesn’t sit around here cheaply, and I’m a much happier project manager when it’s moving.”
Software support
Tensar also offered full-lifecycle support for the project via its Tensar+ software, a free design platform that provides engineering rationale behind the methodology.
Tensar+ brings together decades of accumulated research and study into the design of geogrid-stabilised solutions, quantifying the benefits of stabilisation in terms of cost, time and carbon emissions based on a project’s specific characteristics. The platform’s road design and construction software module allows engineers to explore project parameters such as specifications for stabilised layers before construction has even begun.
“By working out the differences in volume, from thickness savings with the geogrid compared to a traditional option, you can clearly see those savings,” Buckley said.
“And for a lot of renewable projects, it’s also about community engagement; it also compares truck visits for dumping and importing aggregate, along with fuel and water.”
According to Charmaine Fogarty, Tensar’s Area Sales Director for ANZ, Tensar InterAx Geogrid and Tensar+ form a holistic, value-engineered proposition for projects such as Uungula.
“Utilising the application design in Tensar+ software, at the preliminary stage, provides reduced construction materials, time and carbon emissions where low value CBRs are inherent in the subgrade, and therefore we are able to offer on-site installations and support to the successful earthworks civil contractor,” she said.
“We offer a Test Drive Program, where we’ll provide rolls of Tensar InterAx at no charge as part of the overarching customer service. These trials act as a similar process as passing a proof roll, to ensure construction plant can access the site in the early phase of the road works.”
That’s why Fogarty believes Tensar’s work is not just about the product it supplies to its partners.
“It’s a whole-life project,” she said. “Because Tensar is involved early in project development, we can solve engineering problems alongside the relevant teams. We’re here to assist, to educate and to give back to the community.”
