A 2.5km problem
A common issue for contractors is finding the best balance between cost and quality. As infrastructure specialists and designers, that’s one of our particular areas of expertise. Our contractor clients faced the extra pressure of enhancing the A465 trunk road through a World Heritage Site. Our critical eye brought significant, cost-saving benefits to the most challenging component: the Clydach Gorge. The solution for dualling the highway in this steep, narrow and heavily designated site – a split-level carriageway – achieved an environmentally beneficial neutral cut and fill balance. But the resulting retaining wall – up to 11m tall and nearly 2.5km long – could not be bare-faced concrete. The structure needed to blend. But the costs were prohibitive.
Identifying savings
Our approach was a compromise on cost without compromising on quality or aesthetic. If cladding the entirety of the wall would be too expensive, perhaps there was a design which would suit the dramatic setting while bringing down the costs.
By giving precast concrete panels a simple textured finish – one that’s legible to drivers at high speeds and which echoed the stone bedding planes – we could mirror the gradient of the gorge. Then we introduced feature sections of stone-faced cladding, identifying changes in the underlying rock strata. The design achieved the support of all three planning authorities and the Design Commission for Wales. It also improved safety during construction and resulted in a saving of more than £1m to the public purse.
Stakeholder scrutiny
The scheme’s sheer scale and its location inside Wales’ National Park guaranteed that any proposals would receive detailed scrutiny. It would also automatically be the subject of a public enquiry, with the quality of proposals led by the Design Commission for Wales and The Parks Authority.
The contractor-led team decided that, with our experience in presenting proposals, communicating concepts and interpreting feedback, we should lead all stakeholder presentations and discussions. By guiding the interaction, we were also best placed to ensure the design developed in the direction which would keep all parties happy.
Public inquiry
All of our significant stakeholders supported the scheme going through public inquiry with no significant objections presented. Commenting on Knight Architects role in the project the Design Commission for Wales gave the following endorsement:
“We note that this is the first highway project on which the Welsh Government has employed an Architect, and that the expertise brought to the table has significantly refined the design outcomes.”
