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Nant Ffrancon retaining walls, Snowdonia.

The retaining masonry walls at Nant Ffrancon were designed between 1815 and 1830 by Sir Thomas Telford, as part of the A5 between Shrewsbury and Holyhead.

At an altitude of 300m, along a steep mountainside, the retaining walls along the U shaped glaciated valley were constructed so that the A5 could maintain a gradient of 5%. At the time of its completion, the A5 was described by Sir Henry Parnell as 'a model of the most perfect road making that has ever been attempted in any country'.

Assessment revealed that the walls were suffering from major bulging and cracks. Glass fibre reinforced plastic nails were stitched through the walls to secure them to the rock face. 'You can just about make out corks on the face of the wall which anchor the nails, but apart from that there is very little evidence of stitching,' said Paxton.

Local contractor Colin Jones Rock Engineering carried out the work for 1.1M. Reconstructing the retaining wall would have cost three times as much. Schemes using innovative but cheap techniques were an important criteria for the award. Local authority resources for bridge renovation are forecast to remain very low, said Paxton.

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