A major new interchange on the A90 trunk road south of Aberdeen has been completed using an innovative slope stabilisation / erosion protection system from geotechnical specialists Maccaferri.
The £12m Portlethen Interchange has been constructed to provide road access to a new residential, commercial and retail development in the village of Portlethen, eight miles south of Aberdeen. Over 800 houses are being built there by Scottish developer Stewart Milne Group.
EROSION CONTROL MATTRESSES
Almost 800m² of Maccaferri Geomac erosion control mattresses were incorporated on the southbound off-slip embankment. Geomac mattresses are large flat wire cages, similar to gabions, 6m x 2m x 0.23m, lined with filter and filled with stone and soil. When installed and seeded, they create stable erosion protection panels of retained and encapsulated topsoil that promote rapid vegetative growth particularly on wet slopes and, in the case of the Portlethen Interchange, on steeply sloping dry embankments.
The Portlethen Interchange was constructed as a cut and cover project with the south-bound carriageway installed first, followed by the northbound, with live traffic movement throughout the operation. Extensive groundwater control measures were required in the 7m deep cutting due to the high water-table level in the area.
The proximity of nearby houses also meant that a steep, 65° embankment was required on the southbound off-slip. This was excavated in 1.5m deep stages to allow the Geomac mattresses to be fixed as work progressed. Dywidag soil nails 8m to 10m in length were drilled and fixed to the Geomac mattresses, creating an efficient, stable structure.
Explaining the selection of Geomac mattresses, Alan Blair, Technical Director of Consulting Engineers Fairhurst Partners, who designed the scheme, said: “Because of the importance of A90 Dundee to Aberdeen trunk road, we had to have Transport Scotland Approval through the Scottish Executive for all the elements of the design. The Maccaferri Geomac system is the only one of its type using products with BBA Roads and Bridges Accreditation. It has a 120-year design life so we were totally confident of its long-term performance capability.
“Transport Scotland also insisted on a green solution and the Geomac System gives us this. It really ticked all the boxes from a design, performance and appearance perspective,” concluded Mr Blair.
Morgan Est, one of the UK’s leading providers of infrastructure services, were the main contractors for the Portlethen Interchange with Maccaferri Construction undertaking the Geomac installation.