Motorways are the main road network for transporting goods, services and people. At 374 km long, the M6 is the longest and one of the busiest motorways in the UK. Beginning in Coventry, it links Birmingham, Chester and Manchester to Carlisle and the Scottish border.
Highways England’s £7-billion smart motorway programme aims to overhaul the motorway infrastructure. One of the schemes is to widen the M6 at junction 14 to accommodate more traffic by converting the hard shoulder to create a fourth lane.
RSK applied its experience to the section that negotiates a low-lying flood plain, a river and a railway line by a series of three viaducts known as the Creswell Viaducts. Engineers will widen two viaducts by about 6 m and their associated embankments to accommodate a change in layout.
RSK’s engineers transported specialist equipment, including a long-reach excavator that enabled digging on steep slopes, and completed dozens of investigations and ground work, including
• drilling cable percussion boreholes, down to 50 m, and extending them by rotary coring
• pavement coring in the hard shoulder
• conventional machine-excavated trial pits plus embankment slit trenches using a long-reach excavator
• in-situ testing and static cone penetrometer testing
• constructing sheet-pile-shored trial pits, excavating beneath pile caps in header boxes and testing piles using acoustic techniques
• geotechnical and geoenvironmental laboratory analysis.
RSK then completed specialist investigations of the embankment and pile foundation structures through dynamic probe penetrometer testing around the viaduct foundations and testing through the embankment slopes to ascertain the extent of the underlying piled concrete slab. Using the long-reach excavator, engineers were able to drill boreholes at steep and unconventional angles (18.9–43°). The inventive solution negated stability risks and anchoring needs inherent to slope-climbing drilling rigs, and the need to access the work areas from the motorway carriageway. RSK delivered its remit safely and without incident.