This design and build bridge spans 200 metres of the Walkham Valley over the River Walkham at a height of 24 meters. It replaces the original Gem Bridge, which was built by Brunel in c.1891 and demolished in the 1950s.
The new bridge was designed to echo the original Brunel design and has a concrete deck with steel lattice girder arrangement, supported on slender concrete columns. The bridge was constructed using Odex piled pier bases with four in-situ concrete piers, which vary from 10m to 20m in height. The abutments are formed from reinforced earth using keystone blocks with geogrid straps, with the bankseats constructed out of reinforced concrete. The superstructure is formed from box section steelwork, which was fabricated off-site (apart from on-site bolted splices) with the deck being constructed from precast deck unit with an in-situ stitch pour after installation.
The site was within Dartmoor National Park, adjacent to an SSSI; we prepared an environmental strategy for the project to ensure the ecological and heritage requirements of the site were met. This included carrying out bat surveys and providing protection for trees.
The site was also under an archaeological watching brief due to the historic original bridge; an archaeologist monitored the excavations and a Devon CC representative monitored the site.
To enable the construction methodology/sequencing to work while protecting the river we installed a Temporary Haul bridge over the river which allowed an 80te Crawler crane to access the south bank.
The Gem Bridge was named 2013 British Construction Industry Civil Engineering Project of the Year (up to £3m).
Devon County Council