Case Study Huddersfield

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 serious undertaking.

The Optera Solution
Optera surveyed the site and established the geology before designing a remediation scheme.

The solution involved stabilising the failed slope, using ground-anchors and reinforced Geo-mat, with 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/vegetation and 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 through the overburden and into the bedrock, where the hollow-bar anchors were grouted into the rock. Reinforced Geo-mat was then secured to the face of the failed slope to stabilise the ground and ensure the safety of operatives working below.

A reinforced-concrete ground beam was then 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 EPS 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 EPS fill and topsoil.

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