Creating stable ground for onshore windfarms

A major challenge for many onshore wind farm projects is how to support the massive cranes needed to lift turbine sections into place. Geosynthetic cellular foundation mattresses can be the answer.

As I discussed last week geosynthetic cellular foundation mattresses are a proven solution to meeting the challenge of providing stable temporary working platforms capable of supporting heavy loads over weak ground.

Onshore wind farms are a case in point. Typically built in remote areas (and often on weak and variable ground), with little or no existing infrastructure, getting plant, equipment and the heavy turbine sections to site is a major obstacle. Once a wind farm is operational, access continues to be required for regular maintenance and, in some instances, installing newer, larger turbines in the future.

Unsealed temporary access roads, compounds and working platforms are therefore a critical aspect of enabling works. Solutions need to mitigate settlement, be quick and easy to install and must also minimise the amount of soil needing to be excavated (and removed from site) and minimise the amount of imported engineering fill required.

These temporary structures also need to carry huge loads. Construction of modern wind turbines often requires cranes weighing more than 500t to lift turbine sections into place.

Along with mechanically stabilised layers, geosynthetic cellular foundation mattresses offer a range of benefits over traditional ground improvement solutions, such as ‘dig and replace’, soil mixing and piling. Not only do they improve bearing capacity and increase stability, but also reduce both platform settlement, by allowing for even and controlled settlement under the heavy loads.

The geogrid formwork that later gets filled with aggregate can be installed by hand, in all weathers, directly on the ground, saving time and money.

Excavation of unsuitable soils is minimised and less engineering fill has to be imported. Additionally, cellular mattresses can be filled with a wide range of granular materials, including those sourced from on-site borrow pits, which avoids having to import expensive fill over long distances or the use of recycled aggregate. And of course, fewer (and shorter) lorry movements means lower CO₂ emissions, helping reduce the carbon footprint of a project.

Stratum delivers versatile working platforms for Ostercappeln wind farm

A Tensar Stratum cellular foundation mattress provided stable, and versatile, working platforms for the Ostercappeln wind farm in Northern Germany, after piled foundations were ruled out for being too expensive. And, as piles had to be installed in positions specific to the heavy cranes lifting the turbine sections into place, the use of other crane types in the future – for maintenance and upgrades – would be limited.

Installing a Stratum cellular foundation mattress, on the other hand, meant that bearing capacity of the platform installed on the underlying weak and saturated soils was improved across the whole area, allowing cranes to be positioned anywhere on the platforms. Plus, Stratum was much easier and faster to install than piles, with only minimal ground preparation and no need for heavy piling equipment, which made it more economical too.

The full case study can be downloaded here.