Highways Magazine – Denbighshire and Brett Landscaping complete high wire resilience act
Earlier this year, Brett Landscaping completed work for Denbighshire County Council (DCC) after two significant landslides destroyed part of an unclassified country road in a very precarious geographic location.
About 55 meters of the single lane road between Saron and Cyffylliog in the county had to be rebuilt quickly after it fell down a slope into the river.
There was a significant landslide in the region in November 2019, followed by another in February 2020.
The Welsh government granted Denbighshire £ 1.3 million to deal with the effects of the flooding and the council provided £ 450,000 for the landscaping work by Brett Landscaping.
The work to repair the damage was completed between September 2020 and January 2021.
Around one meter of the width of the road was lost in the landslide – to three meters. Although the depth of the landslide was relatively shallow, the damage was great, and trees and shrubs underneath were displaced due to the sheer mass of soil that moved.
The damaged road section required a new foundation and prefabricated retaining wall units with anchors to laterally stabilize the retaining wall and the soil nails on the steep dam below.
Denbighshire contacted Brett’s team to discuss options for installing a curb restraint system that could be used in conjunction with the structural and geotechnical design proposals to restore the road.
Council engineers and Rock Engineering specialists discussed the containment design options with Brett’s expert design team to agree on a working solution that could be implemented in this restricted location.
Brett recommended positioning the twisted Trief GST2A units in front of the prefabricated retaining wall. The wall would protect them and the parapet from impact damage, and would keep stray vehicles from driving off-road and down the steep slope.
An option to install guardrails was considered, but the council decided that retaining wall units in pre-formed sections would be a more workable and less expensive approach and would aid the speed of installation
The tread pattern is intended to pinch the tires of impacting vehicles and ensure that they do not leave the road.
Bretts Trief GST2A anchors were used to anchor the curbs to a new reinforced curb foundation that offered greater impact resistance.
The GST2A units were preferred to other pre-built units because of their size and profile, as they were effective in withstanding the impact of the large farm vehicles that regularly drive on the road, Brett said.
Jamie Gledhill, Technical Director at Brett Landscaping, said: ‘We were delighted to be able to provide design support and a solution for DCC and Rock Engineering.
“Brett’s Trief Containment curbs have been shown to protect structures, edges and pedestrians from vehicle intrusion, and Brett has found solutions for our customers in the past.”
Normally, trief would require a concrete underlay of at least 230mm, but the additional structural reinforcement meant this was not essential.
The trief curbs were poured against the reinforced concrete retaining wall units, each of which was reinforced by a ground anchor that provided lateral resistance.
Brett said the tight connection between the curb and the wall meant that any impact with the curb would divert the force into the wall and anchor. These forces would in turn be reduced by the dowel inserted in the curb.
Part of the work also included having Brett help ensure that the width of the carriageway was not affected too much once the installation was complete.