Hendy Concrete Canvas Culvert Repair Works

Hendy Concrete Canvas Culvert Repair Works

In the midst of excessive rainfall, frequent storms and flooding, the invert of this 70m corrugated steel culvert, under the M4 Motorway near Hendy, Pontarddulais in South Wales, had deteriorated considerably over the years. Our client, Knights Brown, turned to Kaymac to make use of our specialist expertise in water-based remediation works, to repair the culvert and install Concrete Canvas® liner to protect from future erosion, quickly and safely. 

Access to the site compound from the main road included the removal of 5m of hedge line together with 3 fence posts and rails. Then mobilisation of the site office and store was lifted into place.  A scaffolding stairway from the field into the upstream entrance of the culvert was assembled to allow for access.

Sand filled polypropylene bags, placed upstream of the weir, stemmed the flow of water into the culvert, and allowed for pumps to carry the water away from the working area within the structure and to the downstream outlet. Environmental protection measures were put in place to catch any suspended silts that may be over pumped.  

Once the culvert was dry, our operatives had to expose the corrugated steel invert. This involved a decking system put down on the invert so to access and remove the material by hand to the downstream outlet. The invert was then pressure washed to remove any marine growth, debris, oil and grease etc.The grout was then applied by hand to a thickness of 75mm, up to a height of 750mm, along the entire length of the 70m culvert.

With the surface finally prepared, the Concrete Canvas was ready to be laid. Being a confined space, access was naturally limited, meaning the team had to carry and place, each length of canvas by hand. The first strip of canvas was laid on the invert transversely with an overhang extending into the apron. It was then formed around the headwall to suit and fixed into place. The second strip of canvas was then placed over the first with a suitable overlap, and the process repeated for the entire 70m length of the culvert. To help secure the canvas in place before hydration, a timber batten was drilled and fixed over the canvas and into the corrugated steel.