 |
Realignment of the popular A7 trunk road was required to improve the safety, comfort and reliability of journey times on the A7. This involved eliminating several dangerous bends at Auchenrivock, Dumfries and Galloway. Adoption of Tensar International’s low impact Tensartech slope and wall systems avoided potential possible environmental problems with the River Esk.
The A7 is a popular route for tourists as well as a busy road to Edinburgh. At Auchenrivock, south of Langholm, the road runs alongside the river Esk and over several culverted feeder streams which contain important spawning gravels for migratory fish.
The Issue
Embankments up to 20 metres in height were required to maintain acceptable road gradients on the new road sections. However, conventional shallow slope designs for new unreinforced soil embankments and retaining walls would have required long culvert lengths. In addition, where the carriageway was being widened, an existing culvert would have to be lengthened significantly.
Over-long culverts would have deterred any migratory fish from entering in search of the upstream spawning gravels. They would also discourage fry from venturing downstream on their way to the sea to feed and, so, the integrity of the river as an amenity and environmental asset would have been put at risk.
Mammals, particularly otters, would also be disinclined to enter long dark tunnels and would seek to go over ground with the likelihood of becoming road kill.
Problem Solved
When asked for a solution, Tensar engineers proposed a combination of Tensartech wall and slope systems. By steepening slopes, culvert lengths could be reduced by around 40 percent, thus assisting fish migration. In addition, this solution enabled the use of locally won fill composed of sands, gravels and glacial till rather than high grade aggregates. As well as less materials cost, by reducing vehicle transport movements on and off-site for the fill, the impact and CO2 footprint of the project were minimised.
For slopes with less than 1:1 gradient, the Tensartech NaturalGreen system uses Tensar RE uniaxial geogrids to reinforce the soil for internal and global stability. Tensar Mat anti-erosion matting was then installed on the topsoil surface to provide protection and assist the establishment of natural vegetation.
By exploiting the versatility of the Tensartech systems, local design variations could be accommodated. An example occurred where new concrete bridge abutments resulted in small areas of slope greater than 1:1; here a Tensartech TR2 wall reinforced soil structure, with a steel mesh facing, was quickly designed and installed.
In addition, to accommodate the widening of the road where required, a Tensartech TW3 modular concrete block facing wall was built in front of the existing wall. The RE uniaxial geogrids were then attached to the existing wall and the new facing wall, to create a reinforced soil mass anchored into the original construction. Above this, a vegetated slope was created with NaturalGreen, to finish the installation.
DETAILS
Contractor: Morrison Construction
Client: Transport Scotland
Designer: Dumfries and Galloway Council, DGDesign
Slope and Wall Design: Tensar International
ABOUT TENSAR INTERNATIONAL
Tensar International is part of Tensar Corporation, a leading global developer and manufacturer of proprietary, highly engineered, non-traditional site-development solutions for infrastructure end-markets, including transportation, commercial and industrial construction. Tensar provides its customers with an integrated suite of innovative products, technologies and application expertise for a wide variety of end uses, including high performance roadways, earth retention structures, building foundations and erosion and sediment control.
In 2007, Tensar launched TriAx™ a new geogrid which Tensar believes offers superior performance in multi-directional stiffness and aggregate confinement, which enables better radial load resistance, resulting in a reduction in aggregate base thickness and improved resistance to rutting. The company also offers a comprehensive design service, technical seminars and on-site support, as part of a range of support services. Tensar International, formerly The Netlon Group, was founded in Blackburn, Lancashire, in 1952.
PRESS CONTACT
Chris Sanders
IAS B2B Marketing
+44 01625 578 578
Fax: +44 01625 578579
chris.sanders@iasb2b.com
