The bridge is located on the R335 in Delphi Co. Mayo and spans the Bundorragha River. The structure comprised a 9.7m span, 7.35m wide masonry arch bridge. The springing point was approximately 0.45m above riverbed level, and the crown of the arch is a further 2.74m above the springing point.
Stones from the voussoir on the downstream western side and upstream eastern side have come loose and are to be replaced. Some of the loosened stones were present on site but others had to be made. A large scour hole to the upstream eastern side of the bridge, in the riverbed, was infilled with large diameter rock (diameter to be 500mm min).
Drilling and grouting of the arch barrel was conducted and the scour aprons were drilled and grouted to both abutments. The existing grass verge were removed and 2 rubbing strips installed. The cracked parapet to the downstream western side also had to be repaired.
A large part of the planning and the success of this project was the temporary works. The provision of temporary works to control the flow of water at the bridge was paramount to the success of the works. An upstream dam funnelled water into 4 no. 1m diameter pipes which bypassed the water to the downstream end of the bridge. 2 no. downstream dams were provided thus resulting in a dry working environment around the bridge. The lower of these was required to maintain water in the pipe to prevent irregular flow. MEIC Ltd kept the work area between the 2 upper dams pumped. This pumped water settled in a settling tank before discharge back into the river. The dams were constructed of large diameter stone and sand bags.
This bridge was located on a tourist route and was kept open at all times. MEIC Ltd. as part of the contract prepared a detailed Traffic Management Plan and implemented it in order to keep the bridge open.
The obvious constraint was that the work had to be carried out in a River. The method of construction using temporary works is discussed above. A major environmental constraint was also present on the project. It was of paramount importance in carrying out these works that silt was eliminated from discharge into the river. The most important fresh water pearl mussel colony in Europe lay downstream of the bridge. Any silt discharge or disruption to the river bed would kill this colony.
Malachy Walsh and Partners
November 2008 – November 2009
? 88 000
Delphi, Co. Mayo
January 19, 2021