Scour Assessments, South Wales

In August 2019, Dyer & Butler’s Rail Division was instructed to assist JBA in undertaking a number of scour assessments under Network Rail’s Minor Works Framework within the Wales region. This was to ascertain the integrity of the structures following the removal of material from the river bed and banks surrounding the bridges foundations by the action of water. Scour is the leading cause of bridge failures in the last 100 years in the UK.

The works included carrying out visual site surveys, topographical surveys and carrying out destructive testing works including coring operations to determine the depth of the existing bridge foundations.

The information gathered from each of these surveys was then submitted to JBA in order for them to undertake Hydraulic modelling to provide a detailed assessment report to Network Rail.

The scour assessments were undertaken at ten separate, mainly listed bridges within the Wales region. Each of the visual and topographical surveys including the coring works were carried out using safety lines with foot entry into the rivers.

Where the water was inaccessible for foot access due to deep water, safety boats were used instead.

At one site along the South Wales Main Line (SWM2) near Lydney, rope access was used to undertake coring works and assess the structure due to the tidal restraints and unstable mud banks. Sonar surveys were also carried out where the water levels under the bridges were very high.

Following the scour assessment surveys, Network Rail instructed JBA to work in close collaboration with Dyer & Butler to produce the detailed design for scour protection measures to be carried out on three of the structures.