The Problem
In late 2019 following a torrential rainstorm, the retaining wall at the rear of the risk property suffered a serious collapse. The retaining wall formed the boundary between a housing development and a disused stone quarry, with a difference in ground levels between the quarry and the rear gardens of up to 12m. Access was extremely limited and the unstable ground, coupled with the potential for falls from height or further collapse of the ground or wall, made this project a challenging undertaking.

The Optera Solution
Optera surveyed the site and established the geology before designing a remediation scheme. Our solution involved stabilising the failed slope using ground anchors and reinforced geotextiles and building a laterally restrained, reinforced-concrete retaining wall, faced with natural, local stone. Working from the upper level was virtually impossible, so access was negotiated with the quarry owner. Before works could start, we needed to undertake significant clearance of trees and vegetation and to form a ramp up to the base of the wall to facilitate machine access.

The ground anchors were installed by our skilled operatives using a Marini drilling mast, mounted on a 14-tonne long-reach excavator. The anchors were drilled and grouted into the bedrock before reinforced geotextiles were secured to the face of the failed slope to stabilise the ground and ensure the safety of the operatives working below.

A reinforced-concrete ground beam was formed on a suitable rock-step part way up the face and again, this was laterally restrained using anchors grouted into the bedrock. A reinforced-concrete wall was then built off the ground beam, incorporating suitable drainage points to prevent the build-up of water behind the wall. The space between the retained slope and the new structural wall was filled using lightweight fill to minimise the lateral loads imposed. The wall was then faced with local stone – you may notice that the stone we have used is a lighter colour than the rest of the original wall, this is because our stone is newly quarried. It will darken over time to blend in. Once the wall was finished, the garden was reinstated, with a drainage layer on top of the lightweight fill and topsoil.

Project Conclusion
Optera’s highly trained and skilled operatives were able to complete this complex project to the insurer’s and homeowner’s satisfaction. The bespoke remediation scheme included elements to minimise the risk of future slope failures.

“Optera’s highly trained and skilled operatives were able to complete this complex project to the insurer’s and homeowner’s satisfaction.”

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