The ongoing Highways Agency A66 Carkin Moor to Scotch Corner project involves upgrading the original single carriageway to address safety concerns, particularly at junctions and crossings.
Where differential settlement is threatening a remodelled junction, Tensar’s revolutionary new TriAx™ geogrid provides an additional dimension of stability, saving design and build contractors Balfour Beatty Regional Civil Engineering Limited (BBRCEL) the heavy time and costs inherent in conventional remedial solutions, and meeting the Highways Agency’s (HA) key performance indicators.
The widened junction incorporates radiused corners on ‘turn in’ and ‘turn out’, and overlies part of a 7m deep old quarry variably infilled with very-poor quality mixed domestic waste. The original proposals by BBRCEL’s design partner Atkins included excavation, disposal and replacing it with high-quality imported fill, which would have cost hundreds of thousands of pounds and been environmentally undesirable.
With the encouragement of the HA to look at innovative solutions to manage costs more effectively and reduce environmental impact, BBCREL and Atkins consulted Tensar about geogrid solutions. A specific concern of the project was that one leg of the junction runs over the irregular edge of the quarry, with very variable direction of potential instability, while, at the same point, vehicle wheel loadings are also going to be variable in direction.
To meet this problem, Tensar proposed use of its new TriAx geogrid, as a composite structure including granular fill and heavy duty bi-axial geogrid at the base to create a reinforced granular mattress.
Sean McCready, site project manager for BBRCEL, said: "The innovative TriAx solution offers excellent cost benefits of at least 75% savings to the project against very acceptable risk levels. This approach also fulfilled the HA’s objective of looking at innovative proven solutions to drive down cost. We talked this through with Mouchel Parkman – who are charged with the HA’s supervision of the works – as well as Atkins, to come to a joint decision."
The TriAx structural solution not only eliminates the cost, time and excessive transportation required for the excavation proposals but also minimises the undesirable environmental impact of large quantities of landfill disposal, high-quality aggregate extraction and vehicle journeys.