NEW WING WALLS for the Old Quarrington Bridge on the A688 Wheatley Hill to Bowburn Link Road in Co. Durham, required an aesthetic natural finish. Balfour Beatty Regional Civil Engineering used the Tensartech GreenSlope earth retaining system to ensure a highly attractive vegetated appearance, with sustainable construction, saving up to 20% in site time over alternative faced systems.
The new road runs parallel to the A1(M) crossing over the existing road leading to the hamlet of Old Quarrington to the east of Bowburn via the new bridge. The new road opened in October 2008 provides a strategic link between the A1(M) and the A19 avoiding Bowburn.
Design Engineers for Durham County Council were keen on using a vegetated slope solution for the bridge wing walls for aesthetic reasons as the walls are high and are prominent where the road rises up the gradient. Reinforced concrete would have been inappropriate as well as more expensive. Durham County Council prepared a reinforced earth design using a 65º vegetated wing wall slope, which was checked by Tensar. The design sought the optimum solution in terms of appearance and installation costs.
Having previously evaluated wrap-around systems, Balfour Beatty Regional Civil Engineering had found that they were both labour intensive and that the vegetated surface took several weeks to achieve a satisfactory finish. As a result, the project engineers were keen to expand on their earlier experience with Tensartech earth retaining systems and asked Tensar to propose an alternative.
The Bowburn project used locally sourced crushed concrete fill to create slopes up to eight metres high reinforced with layers of Tensar uniaxial geogrid. The geogrids were rapidly fastened with a polymer bodkin joint to the steel mesh facing units which were lined with a composite biodegradeable mat and topsoil layer.
Colin Thompson, Key Accounts Manager for Tensar International concludes: “Tensar has worked closely with Balfour Beatty Regional Civil Engineering and Durham County Council engineers to demonstrate the value of its solutions in performance, cost savings and reducing the ecological impact of this major construction project”.
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