Kaymac Marine & Civil Engineering Ltd were commissioned by Birse Rail to install scour protection to protect the structure from further deterioration. The structure is a 7-span viaduct located on WCM1 at 1m 450yds to 1m 560yds and carries the DF and UF lines of WCML over the river Eden. It is constructed of pre-stressed concrete deck beams on sandstone masonry piers.
An underwater inspection of the submerged elements of Eden Viaduct’s pier faces revealed the structure had a number of significant defects that would have affected its stability and integrity. There was evidence of severe river bed scour which had affected the upstream cutwaters and pier ends of the central piers. This had resulted in undercutting of the bedrock and subsequent loss of the masonry foundation blocks from the piers. In addition, the foundation masonry to the upstream south faces were in danger of collapse due to undercutting of the supporting bedrock and at least one of the blocks appeared to have moved out of alignment.
The piers had suffered from loss of masonry to the north cutwater face and part of the upstream north pier face, probably due to a combination of open jointing and bed scour. An attempt to elevate further damage in this area carried out by others had proved futile, as the Gabion baskets installed had been severely damaged and the fill was spilled over the river bed.
To gain access to the piers, Kaymac installed a temporary rock armour access track. An excavator working from the track then cleared the voids around the piers of any loose debris and masonry. The Kaymac dive team surveyed the piers to confirm the damage and determine the required formwork.
Formwork was then installed to the structure by the Kaymac dive team. Once securely fixed, concrete (with an underwater additive) was pumped into the voids of the piers. Kaymac also carried out various masonry repairs to the structure. Upon completion, the temporary access track was removed from the watercourse. The works were completed with the WCML lines kept open with no delays or stoppages to the rail traffic.