Combigrid® – Construction of Floating Forest Access Road, UK

Foswell Woodland Creation, in the Northern Ochil Hills near Auchterarder, Perthshire, supports Scotland’s effort to expand forest cover. The 125-hectare site requires about 4 km of permanent forest tracks to enable maintenance and, later, harvesting. These must provide dependable access for heavy machinery while respecting sensitive environmental conditions.

Protecting peatlands while crossing ultra-soft ground

Large sections of the route cross peatland –  an irreplaceable carbon store formed over millennia. Conventional road building would excavate peat and import aggregate, disturbing habitats and releasing locked-in carbon, undermining afforestation’s climate gains. Ground investigations by Campbell of Doune showed very weak, variable soils (CBR 1 – 3%), compounding the challenge. The solution therefore had to:

• minimise disturbance to peat and adjacent habitats;
• avoid mass excavation and aggregate import;
• distribute loads over very soft subgrades;
• deliver a durable, low-maintenance track for decades of forestry traffic.

Thinner layers, fewer haul movements, greener outcomes

Working with Taiga Upland and Scottish Woodlands, the design adopted a floating road using Naue’s Combigrid® 40/40 Q1. Instead of peat excavation, the geocomposite is rolled out along the alignment and site-won stone placed directly on top. The track “floats” over weak ground, reducing settlement and surface deformation while protecting the peat beneath.

Naue Combigrid® combines a high-strength geogrid of stretched, monolithic PP flat bars with welded junctions and an integrated, mechanically bonded filter geotextile. The composite action prevents soil-aggregate intermixing, enhances load distribution and enables required compaction on very low CBR subgrades. By improving bearing capacity at the interface, the system permits thinner aggregate layers and fewer haul movements – cutting time, cost and environmental disturbance.

Around 17,000 m² of Combigrid® were supplied in lightweight rolls for rapid installation with a loader and spreader bar. Overlaps are straightforward, and cuts are easily made to suit curves and transitions. Aggregate depths were varied according to measured CBR, optimising material use while maintaining performance.

More value, less impact: Naue Combigrid® reduces material use, accelerates construction, and safeguards peatlands

• Environmental protection: no peat excavation, markedly reduced carbon release and minimal habitat disturbance.
• Geotechnical performance: effective reinforcement over soft ground, improved stability and reduced rutting.
• Resource efficiency: thinner stone layers using site-won material, fewer imports and lower embodied impacts.
• Long-term reliability: a durable access network ready for future forestry operations.

Feedback from site has been strongly positive, recognising a low-impact, high-performance solution that aligns with Scotland’s climate and forestry goals.

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