Surface mining: Agricultural road

Against the backdrop of conventional (costly) constructions in a surface mining (backfillings with aggregate and recycling material) for so-called agricultural roads, a field test with Geoweb (GW30V8) has been carried out.

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Slope Reinforcement and Erosion Protection, Train Robbers Bridge, Ledburn, Buckinghamshire

In January 2004 work started on the West Coast Mainline Route Modernisation project. Part of the project was the reinforcing of the embankment at the infamous Train Robbers Bridge, Ledburn. Network Rail and main contractor Balfour Beatty were looking for an economic and effective solution to the problems of burrowing animals undermining the embankment and potential soil erosion on the steepened slopes. The solution had to be effective and easily installed next to a high speed electrified rail line, robust to prevent burrowing animals and fire retardant in the event of sparks or vandals attempting to set fire to the fibres.

The answer was Greenfix F³ Rockmat a composite of fire retardant sea grass fibres woven into a thick blanket stitched to an anti-vermin galvanised wire mesh. The unique sea grass fibres of European origin are naturally fire retardant and 100% biodegradable within 36-60 months. The blanket is of sufficient density to prevent erosion of the underlying soils and promote the establishment of grasses for long term protection. The upper steel mesh layer provides a highly effective anti-vermin protection layer where rabbits and foxes etc are likely to create slope instability due to burrowing activities.

The slopes were re-graded as a result of the installation of new signalling posts and gantries. 75mm of top soil was placed on the embankment by sub-contractor Joywheel. Greenfix sourced a native grass seed mix which was sewn under the F³ Rockmat as it was installed.

The F³ Rockmat is easily manageable at 25Kg per 30sqm roll. An anchor trench sufficient to prevent burrowing under the blankets was dug at the top and bottom of the slope and Greenfix 300mm timber stakes used to pin the matting to the subsoil. In less than five weeks of installation the embankment was fully vegetated. The grasses grow through the fibres, enveloping the mesh to produce a protected grass embankment reinforced by the mesh but which is visually attractive.