Our work on a high embankment, rather than a viaduct, helped save millions of pounds
When the Highways Agency needed to improve an 11.5-kilometre segment of the A30, Cornwall’s main road link to the rest of the UK, we were brought in to provide detailed design. The project area is at the head of the Camel Valley, a recognised area of high ecological sensitivity. That meant, to protect the local ecology, the road had to cross the valley around 20 metres above the valley floor. The solution? A high embankment.
In the preliminary design phase, the option of strengthened earthwork—using geogrid reinforcement and incorporating imported selected granular fill—was tackled by our partners. In addition, the complex shape of the embankment, with sweeping curves along its width, gave us a particular challenge. Our design used a technique of wrapping the geogrid back over the top of the lift of compacted fill which was then buried by the next lift.
The final structure, at 22 metres high, uses one of the highest reinforced slopes in the UK. With its stream culvert, wildlife underpass, and height from the valley floor, the new A30 embankment keeps Cornwall connected and doesn’t encroach on protected natural habitats.
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