Ramboll engineering has enabled a piece of classic bridge design to be realised at a secluded Dartmoor National Park valley, in the form of the Gem Bridge. This unimposing cycling and pedestrian bridge, with its elegant arches and concrete latticework, draws inspiration from the original Walkham Viaduct, designed by Brunel for the South Devon Railway.
The £2.1m Gem bridge is 200 metres in length, and sits on the 440km cross-Channel Cycle West Vélodyssée route, which will eventually reach from Redon in Southern Brittany to Ilfracombe in Devon. Reaching the two sides of Walkham Valley at different heights, the Gem Bridge required a maximum gradient of 1 in 20.
The site’s steep embankment sides posed a challenge for Ramboll, as well as the mine-shafts that are dotted around the site, which reach depths of 50m. As the bridge is part of a cycle and pedestrian route it connects the two sides of the valley at different heights, so the design had to be managed to ensure a maximum gradient of 1 in 20.
15, 15m long sections of steel truss make up the bridge’s five spans, which measure in at 30m, 40m, 60m, 40m and 30m, and boast a total weight of 150 tonnes. The EDG has worked closely with main contractor Dawnus, as well as TEMA Engineering Ltd. 20 tonnes of scaffolding was installed by Dawnus over a tennis court-sized area in order to support a 250 tonne crane for the job. TEMA Engineering Ltd was then responsible for the high-precision installation the bridge’s sections.
Project Supervisor Ben Naylor said “it was important that in designing the different elements we tried to keep the same ethos that was behind Brunel’s structure. You look for influence wherever you can find it. One thing it always comes back to is the original Brunel structure and trying to tie ours back to that historic one”.