Two markedly different reinforced-soil, embankment solutions from geotechnical experts Maccaferri have been used in the construction of a new traffic relief road for the Port of Wicklow in Southern Ireland.
The solutions – one soft faced, the other hard, have allowed the engineers to solve complex challenges of building the road over poor underlying ground conditions in one area, and in another, through a heavily congested industrial zone where space was at a premium.
The first structure is 10.5m high and comprises Maccaferri Green Terramesh soil reinforcement system in combination with uni-axial geogrids and compacted back-fill. The 550m long embankment raises an existing road to a level which allows it to cross the Dublin to Wicklow rail line.
The Green Terramesh solution creates a crisp, 60 degree battered slope and allowed gradual build up of the embankment levels over some four months to accommodate anticipated settlement of the structure during construction.
The system was chosen in preference to a reinforced concrete or piled structure as it offered significant cost saving advantages in speed of construction, flexibility and its ability to utilise large volumes of materials claimed from other areas of the site.
The second embankment is at the eastern end of the Port Access Road and carries a link from the existing sea road to a bridge over the Broadlough Estuary and a railway line.
Here, Maccaferri designed the engineered retaining walls for the embankment. Because of the limited availability of space, a hard faced structure was chosen, comprising a geogrid reinforced compacted soil core with near vertical, dry built, masonry facing walls The masonry facing blocks – Macwall Landmark, were hand placed to line and level onto minimal concrete footings. Because of their size they could be laid to smooth curves and readily adjusted to achieve the required alignment.
During construction, the geogrid reinforcement tails were placed into a receiving channel on the top face of the block and held in place by means of a polymer locking bar. Corresponding tongues on the underside of subsequent blocks hold the locking bar in position creating positive connectivity, preventing pullout of the geogrid under load and giving the system immense strength.
According to Maccaferri, Macwall Landmark is one of only a handful of retaining wall systems that carry British Board of Agrement [BBA], Roads and Bridges Accreditation, with a design life of 120 years.
The £28m project was designed and project managed by Consulting Engineers Arup for Wicklow County Council and was built by a joint venture partnership between SM Morris Ltd and Coffey Construction.