Earlier this year, Brett Landscaping completed work for Denbighshire County Council (DCC) after two substantial landslips destroyed part of a rural unclassified road in a very precarious geography.
Approximately 55m of single carriageway road between Saron and Cyffylliog in the county needed to be rebuilt quickly after it had fallen away, down a slope into the river below.
There was a substantial landslip in the area in November 2019, followed by another in February 2020.
The Welsh government awarded Denbighshire £1.3m to deal with the impact of the floods and the council put £450,000 towards the landscape work from Brett Landscaping.
Work to repair the damage was completed from September 2020 to January 2021.
Around a metre of the width of the carriageway was lost in the landslip – reducing it to three metres. Although the depth of the landslide was relatively shallow, the damage was extensive and trees and shrubs below were displaced due to the sheer mass of soil that moved.
The damaged section of road required a new foundation, along with precast retaining wall units complete with anchors to provide lateral stabilisation to the retaining wall and soil nails on the steep embankment below.
Denbighshire contacted the team at Brett to discuss options for installing a kerb containment system, which could be used in conjunction with the structural and geotechnical design proposals to reinstate the road.
Engineers at the council and specialists at Rock Engineering discussed the containment design options with Brett’s expert design team to agree on a working solution that was feasible to implement in this restricted location.
Brett recommended dowelled Trief GST2A units to be positioned in front of the precast retaining wall. The wall would protect it and the parapet from impact damage and deflect any stray vehicles from going off-road and down the steep slope.
An option to install crash barriers was considered, but the council decided that retaining wall units in pre-formed sections was a more feasible and cost-effective approach and aided the speed of the installation
The Trief profile is designed to trap the tyre of impacting vehicles and ensure that they do not leave the carriageway.
Brett’s Trief GST2A dowelled kerbs were used to anchor the kerbs to a new reinforced kerb foundation, which provided a greater level of resistance to impact.
The GST2A units were chosen over other pre-cast units due to their size and profile being effective at resisting impact from the large farm vehicles that use the road regularly, Brett said.
Jamie Gledhill, engineering technical manager at Brett Landscaping, said: 'We were pleased to be able to provide design support and find a solution for DCC and Rock Engineering.
'Brett’s Trief Containment kerbs have a proven record in protecting structures, verges and pedestrians from vehicular incursion and Brett has a history of finding solutions for our customers.'
Usually Trief would require a minimum 230mm backing of concrete haunching but the extra structural reinforcement meant this was not essential.
The Trief kerbs were cast against the reinforced concrete retaining wall units – each one of which was strengthened by a ground anchor providing the lateral resistance.
Brett said that the solid connection between kerb and wall meant that any impact on the kerb would deflect the force into the wall and anchor. These forces, in turn, would be reduced by the dowel introduced into the kerb.
Part of the work also involved Brett helping to ensure that the width of the carriageway was not impaired too significantly once the installation was completed.