River Leri Viaduct (Underbridge No. 210) carries the SB A2 railway line across the River Leri at Ynyslas, near Borth in North Wales. The structure is a seven span timber viaduct 42.75m in length and is 4.31m wide. Several of the main pitch piles and main cross head timbers required replacement due to decay and attack by marine boring worms (gribble).
Following a structural survey being carried out on the bridge, it was found that several of the structural timber members (including groins, crossheads, piles, corbels and cross bracings) were in urgent need of replacing.
Kaymac were commissioned by McApline Rail to complete these works. To enable the works to be carried out, a complete blockade was placed on the railway line for 9 days.
Prior to the commencement of the works, Kaymac carried out enabling works which included constructing 2 Nr piled crane platforms on the marshland either side of the river for 70 and 90 tonne crawler cranes and also systematically loosening and replacing the worst of the corroded bolts adjoining the members.
At the start of the possession, the deck was then jacked up off the pier trestles on a temporary support system installed by Kaymac, to allow the systematic dismantling of the affected structural elements. The jacking system was founded on concrete blocks placed on the river bed using Kaymac dive teams.
Modular pontoons were used to access the structural elements from the tidal river. The bolts were removed from each section as required and the new greenheart members lifted into place using the cranes.
Once all the members had been installed, the bolts were integrity tested, with any failures being replaced with new. The track was reinstated and the structure handed back to the client before the end of the planned possession.