Case study Horsley Hill Slip

The Bison Precast team at Somercotes supplied bespoke precast concrete retaining walls for an award-winning engineering project to reinstate and improve a key section of road in south Gloucestershire that had been damaged by a landslip. Work began in July 2017 to repair the landslip, which had struck four years previously and reduced the B4058 to a single lane of traffic between the village of Horsley and the town of Nailsworth.

The £550,000 project, led by Gloucestershire County Council, which took more than four months to complete, was crucial to make the road fully usable for motorists, ease congestion and prevent future landslips. Due to the extent of the work, the route was closed to public traffic and the remaining road at the site was completely removed. The existing highway surface was excavated approximately two metres before Forterra’s 94 precast concrete retaining walls were secured to the underlying rock.

Robert Nesbitt, Contracts Manager for Graham Construction, said, “This was a team effort and we put in a lot of work to make sure it went according to plan. I came up with a method of laying precast concrete units onto a rail system, with grouting underneath the concrete to secure them and ensure that once they were in place they didn’t need to be moved again. This saved a lot of time.

“Amey designed the final system based on this idea, and Bison Precast manufactured the concrete precast units to the exact specifications. At peak performance, we managed to lay 40 precast units on the site in just one day, because the system we’d planned together worked so well in practice.”

Mark Shepherd, Major Projects Manager for Bison Precast, said, “We had to adapt our existing moulds for this job, which featured a unique use for the L-shaped retaining wall units. Effectively, the foot was used as the wall of the system, and vice-versa, creating a wide trench for run-off at the site.

“Time was of the essence for this project, as it was vital to cause minimum disruption for local people for whom this route is essential.

“Good communication between designers, manufacturers, the local authority and the site team ensured the project went as well as possible given the quite difficult circumstances.”

David Cain, contractor on the project, said, “The L-shaped precast concrete units supplied by Forterra had to fit securely and precisely to ensure the drainage system was 100% effective, and when it came to lower the units in place at the site they came together perfectly with no issues.

“Due to its location and the conditions, this was a very challenging and interesting project, and it was satisfying to get it completed to plan. The local response has been very appreciative, and I’ve even had some messages of thanks and presents from local people thanking us for the good work we put in to fix this road, which is so important to them.”

Local residents were consulted fully on the project before and during the work, with regular updates and the chance to give feedback via the local authority.

The road was reopened in December 2017. The Horsley Hill project went on to win the 2018 Ground Engineering Awards’ category of UK Project with a Geotechnical Value of up to £1m.

The Awards’ judges crowned the project as the “clear winner”, due to “excellence in every aspect of the project”, “a robust solution with good collaboration throughout,” and “excellent value for money delivered on this scheme.”