Construction of 3.2km of dual carriageway on the A9 Perth to Inverness trunk road network, including realignment of 1km of the National Cycle Route NCN7 through a narrow site corridor within the Cairngorms National Park and Lough Etteridge SSSI, all whilst maintaining 24-hour two-way traffic on the A9 trunk road.
Work comprised the adaptation of 3.5km of single carriageway to a dual carriageway standard involving both on and offline working. The works also involved the construction of a cycleway with steepened earth retention along the extent of the route immediately adjacent to the Perth to Inverness Network Rail line, along with hard and soft landscaping works including 120,000m² of top soiling. All works were undertaken within the Cairngorms National Park, a Site of Special Scientific Interest.
The project team successfully delivered the works by adopting a number of innovative design and construction solutions, in particular the approach taken to maintain two-way traffic at all times through the works, which was a key requirement under the contract. The new dual carriageway horizontal and vertical alignment posed significant buildability issues over part of the works in this regard. To overcome this challenge, we developed a temporary traffic management (TTM) phasing strategy where northbound traffic was diverted onto an existing cycleway upgraded to take single lane traffic. This allowed northbound traffic to be diverted over two kilometres of the scheme, whilst southbound traffic was accommodated within the new dual carriageway corridor. This temporary works solution led to the safe delivery of the project with respect to both road users and workers on site, while managing the challenges posed to maintain two-way traffic.
A ‘zero offsite disposal’ strategy was implemented with maximum re-use of existing pavement and surplus Class 1 material through on-site screening, processing and washing (drainage stone) . A total of 50,000m³ of disposal to landfill and a reduction of imported aggregate of 35,000m³ was achieved, equating to a carbon reduction of 2,224t of CO2 in transport emissions.
- 65,000m² of a flexible composite pavement
- Major cut/fill earthworks 65,000m³
- 8km carrier drainage up to 600mmØ
- Eight pre-cast culverts (up to 1500mmØ)
- 1.2km of BT Open reach fibre optics ducting
- 850m of pre-cast concrete “Enviro” kerbs
- Soil nailing and rock bolting adjacent to a railway line and overhead electricity pylons
- Trenchless underground duct installation
- Realignment of 3.6km of cycle track adjacent to a live railway line
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