Roughan & O'Donovan-AECOM undertook the bridges/structures, road alignment, earthworks, drainage and pavement design for the non-tunnel elements of this scheme comprising:
- 10km of approach roads
- 4 interchanges
- 2 toll plazas
- 10 major bridges
- 3 creek crossings
- 500m long rockfill causeway built using “wet construction” in Bunlicky Lake
We also provided resident site staff to supervise the execution of those works, in accordance with the Design and the Works Requirements.
Structures design included retaining walls, culverts, steel gantries, precast and in-situ bridges.
We pioneered long span integral bridges and provided a pair of 200m long fully integral viaducts, namely, Structure B11 Limerick Southern Ring Road, which was awarded the ACEI President's Award for Innovation in Design in 2011.
Foundation design included significant piled foundation and pads on direct foundations.
We completed the arterial drainage, mainline drainage, flood risk studies and hydraulic analysis to size bridge openings over creeks and rivers and all culverts required by the scheme.
We undertook the detailed design of the approaches and accommodation structures including:
- Design of significant elements of roadworks and realignment of existing roads at tie-ins
- Pavement design and all street furniture
- 200m long rock cutting, including rock bolt strengthening below bankseat foundations for a 46m single span bridge
The necessity for high embankments (up to 10m) on significant depths of soft ground (up to 15m) required extensive ground improvement techniques, including:
- Multi-stage embankments on soft ground, with prefabricated vertical drains and geosynthetic basal reinforcements
- Temporary surcharge fill (2 to 2.5m typically) to reduce long-term secondary creep settlements
- Continuous monitoring of performance by means of piezometer, inclinometers, settlement plates and survey monuments