Geotechnical condition surveys had highlighted the need to repair a failing slope adjacent to a major trunk road. Falling rocks and masonry, caused by erosion and lack of adequate drainage systems posed a serious danger to traffic without immediate action to remediate the issues.

Following the descaling of the face, remediation options included installation of rock bolts and reinforcing mesh, a geotechnical drainage system to prevent further erosion, with either a masonry facing with concrete infilling of the void, or a structural sprayed concrete facing, with a final layer to be coloured and carved to match the existing random course stone wall. The client chose to go with the sprayed concrete option.

Our previous experience in the construction of climbing walls, urban regeneration and natural rock formations within zoo enclosures meant that we could offer the structural sprayed concrete element of the design together with an aesthetically pleasing finish at the same time. 

This would shorten the works programme, reduce the need for lengthy traffic management, with all the associated delays, and potentially offer a longer design life to the slope facing.

One major issue was the height of the slope at the north end which was over 9.00 metres high, and would be difficult to spray safely using a traditional access system such as a MEWP due to the weight of concrete in the delivery hoses, which would exceed the capacity of the basket weight limit. GSSL opted to use a robotic spray system to overcome these issues, with the additional benefit of further reducing the anticipated works programme.

The final colouring and carving works were completed using the dry spray method (Gunite) which was carved and coloured using proprietary concrete colour dyes to match the original stone coursework found on other sections of the rock face.