Widening the M6
Motorways provide 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 near 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 this section, which negotiates a low-lying flood plain, a river and a railway line via a series of three bridges known as the Creswell Viaducts. Engineers will widen two of the viaducts by about 6 m and modify their embankments to accommodate a change in layout.
RSK’s ground engineers mobilised specialist equipment, including a long-reach excavator that enabled digging on steep slopes, and completed investigations at multiple locations, including: drilling cable percussion boreholes down to a maximum depth of 50 m, extending many by rotary coring; pavement coring on the hard shoulder; machine excavating conventional 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; and geotechnical and geoenvironmental laboratory analysis of soil, rock and water.
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 specialist drilling and probing apparatus fitted to the boom of the long-reach excavator, RSK was able to drill boreholes at steep and unconventional angles (19–43°). The inventive solution eliminated the need to employ slope-climbing drilling rigs with their inherent stability risks and anchoring needs, and to access the work areas from the motorway carriageway. RSK delivered its remit safely and without incident.