Ground stabilisation for Heads of the Valleys road upgrade
A 106-km stretch of road known locally as the Heads of the Valleys links rural villages and towns to urban centres in Wales and beyond to the English Midlands. The Welsh government’s £800-million upgrading project is ambitious in scope: the three-lane road is being converted into a dual carriageway.
CAN, an RSK company, has worked as a subcontractor for Costain on the stretch of road from Brynmawr to Tredegar. To date, the geotechnical specialists have worked on more than 40 individual sites along the current phase of the road widening scheme and carried out an assortment of diverse ground stabilisation techniques. Because of the road’s steep topography and the area’s complex geology, the team of expert technicians had to use several different approaches to widening the road.
As the new road route required frequent cutting into the mountainside, the road boundaries needed to be significantly steepened, which created inherent instability and the requirement for reinforcement. Consequently, CAN installed soil nails, gabions, rock bolts, sprayed concrete and catch fences, carried out bulk grouting and erected erosion matting and rockfall netting. When the road needed to be built outwards into Clydach Gorge, CAN stabilised the newly formed slope to stabilise the roadside.
The extremely variable ground conditions meant that numerous drilling methods were necessary. Because the roadside is progressively cut downwards, engineers used hydraulic drill rigs mounted to excavators to do most of the drilling working from benches cut successively further down. Where access was obstructed or where drilling was required to be carried out on cliffs, bespoke, A-frame, face-mounted drilling rigs were suspended at height from wire cables.
Mindful that the site was active and the public needed to use the road, CAN installed several temporary works designs to ensure the safety of the workers and the public. This included a 230-m-long catch fence that prevented rockfall onto the live traffic lanes during part of the work. Wet weather produced small landslides frequently during the four years that CAN worked on-site, but the team acted quickly to stabilise the areas so that work could continue safely.
During the project, CAN pumped more than a million litres of grout and installed more than 36,000 m2 of rockfall netting and almost 11,000 soil nails and rock bolts, a total of 44 miles drilled.