N17 / N18 River Nanny Bridge, Galway
The N17/N18 Gort to Tuam PPP Scheme forms a 57km section of the Atlantic Road Corridor. We were engaged by DirectRoute PPP Co. as Designer of the scheme including the River Nanny Bridge.
The bridge carries the N17 Tuam Bypass carriageway over a new access track and the Nanny River. The bridge has a clear span of 17.2 m and is set at a skew angle of 17.6°. Overall (skew) span is 20.775m.
The Nanny River presented challenges in addressing the environmental sensitivity and the particular geotechnical risks present at the site. The Nanny River is a Special Area of Conservation (SAC). The design ensured, even in the most difficult ground conditions, that the river was maintained undisturbed during construction of the bridge crossing.
It was decided to incorporate temporary sheet pile wall into the permanent works. For the temporary works the sheet piles were tied across the river to retain the river and its channel and banks.
In the permanent situation the 10m high road embankment would result in higher earth pressure on the embankment side which could not be retained by the sheet piles. The solution devised was to tie the sheet piles back under the embankment with friction ground anchors encased in concrete cast directly against the 6N fill to maximise their pull-out resistance. The concrete surround also acted as a protection layer.
Client: | Direct Route PPP Co. |
Location: | Co. Galway |