Rockley Sands Viaduct Scour

Dyer & Butler were called out by Network Rail via the Wessex Reactive Framework to respond to a sheet pile retaining wall and scour failure at Rockley Sands Viaduct, Poole Harbour using 3000T of rock.

The first stage of the project comprised the inspection of the structure to carry out echo surveys to ascertain the extent of the erosion and failure. This also involved using specialist divers.

The design was developed commencing stage 2 of the 8-week programme. For the next two stages of the scheme we employed specialist subcontractors to repair the scour protection.

We kept all structural monitoring in place until the installation of a grout mattress to prevent further spoiling.

The findings that were made using a sonar survey illustrated on the right, was that the scour had reached a depth of 13 metres in the centre, pulling material out of the broken sheet pile wall.

The existing sound sheet pile area was filled to allow safe access for a small machine to place rock into the scour hole to fill the remaining voids using 60T of 150-200mm, 40T of 1-2T and 80T of 300-400mm stone.

A barge fitted with a 14T machine was then used to install further rock to cap the existing scour protection measures around the structure.

We then mass filled the scour hole that runs through the centre of the bridge which was carried out afloat. The project was undertaken during the COVID-19 outbreak and saw our framework and project teams adapt to undertake works in a ‘COVID Secure’ environment implementing social distancing, deep cleaning and sanitation measures.