THE PROBLEM
Construction of embankments up to 15m high over culverted burns for a realignment of the A7 trunk road south of Langholm. The location of the site meant that the import and export of large quantities of fill and spoil was not practically feasible.
THE SOLUTION
Three different types of Tensartech Earth Retaining Structure were utilised. Tensartech NaturalGreen was used on the embankments with small areas of Tensartech TR2 on locally steepened sections adjacent to structures. A Tensartech TW3 wall was also used to reface widened existing culverts.
PROJECT DESCRIPTION
Road realignment of the A7 to the south of Langholm to eliminate a number of dangerous bends on this important tourist route. Two culverts crossing the deeply incised Docken Beck and Irvine Burns, required high embankments to maintain the road level at acceptable gradients. An existing culvert over Gaber Gill required widening to accommodate the widened carriageway.
During late 2007 and into 2009, Tensar designed and supplied Tensartech NaturalGreen reinforced soil slopes with Tensar uniaxial geogrids and Tensar Mat anti-erosion geotextiles. These new slopes to embankments allowed the desired gradients and falls to be maintained along the trunk road. The Tensartech NaturalGreen slopes were designed using UK highways agency advice note HA68/94 with a 120 year design life for the geogrids which is verified by independent BBA certification. Small areas of reinforced soil with steel mesh facings (Tensartech TR2) were used at a minor road overbridge within the Docken Beck embankment due to local over-steepening of the slopes adjacent to the concrete bridge abutments. This was one of a number of small re-designs necessary to deal with local site conditions.
In addition, a small Tensartech TW3 modular concrete block wall was constructed to accommodate a widening on an existing culvert over Gaber Gill in the north of the site on the original road line. This was constructed in front of the existing road retaining wall with the reinforcement grids extending to the existing wall face.
The fill used for the reinforced soil was mainly locally derived sands and gravels together with some glacial till. This reduced the number of vehicle movements in and out of the site to much lower levels than would have been required using imported fill.
