Challenge

The requirement was to armour an existing Larsen piled sea wall that had become badly holed by the effects of two tides per day in a bay where aggressive wave action caused significant drift of beach material and debris, much of it being infill from failing up-shore gabion defences that was being thrown against the face.

Solution

The solution was to use Leromur retaining wall units, beginning with a 1000mm-wide lower structure featuring a smooth face, this being reduced after 1 metre to split-faced sections of 750 and 500mm width with a face angle of 15°.

The gap between was infilled with recycled aggregate reinforced laterally with Betonap geogrids, the face of the piles being lined with a non-woven geotextile. As the wall met the piles at the top level a precast rollover coping was bonded in place.

The temporary works phase had to manage water inundation on two tides and a 1 metre shift in beach level. The solution was using Pecafil permanent shutters with a 2-stage concrete footing. This created an even bearing and then provided the reinforced base for the Leromur blocks.

By using rapid hardening concrete it was possible to work between tides with a set achieved before vacating the beach. As the wall continued in height the dry laid structure came into its own by enabling tidal wash to over-top the structure but at the same time allowing water to permeate and then seep back through the dry joints on withdrawal.