Finding the missing link

Carillion was awarded the contract to improve the section of highway between Carlisle and Guards Mill, UK, and to bridge the gap between the M6 and the Scottish border. Upgrading the A74 dual carriageway south of Mossband to a three-lane motorway involved a simple method of digging out and replacing weak material to a depth of 1m along the existing road profile. Variable ground conditions at Mossband were more challenging. A complex geotechnical system was devised using band drains, vibro concrete columns, sectional flight auger piles and geogrids for an embankment to support the new viaduct over the River Esk. A new prototype rig from Bauer is being used to install sectional flight auger piles under each embankment in the areas closest to the West Coast Main Line. Stratcaster rigs are being used to install vibro concrete columns further away from the railway. Piles and geogrids will work in tandem to create a load transfer platform beneath the road. The soft ground is expected to consolidate under increased pressure. The process is being accelerated by the installation of Mebra-drain 7007 band drains. Inside the embankment will be Fortrac geogrids separated by imported fill.