HR Wallingford helps protect Sumburgh airport

Sumburgh airport is located at the southernmost tip of the Shetland Islands. The airport runway includes an extension on reclaimed land, and to the east of the runway the design included an outer face constructed of primary rock armour.

Following severe storms over the past two years, damage to the runway extension was discovered and damage was believed to be caused by severe wave overtopping. This washed out filter rock through gabion baskets and also caused movement of the existing ‘reno’ mattress. It was proposed that this damage was repaired using concrete slabs.

HR Wallingford examined the effectiveness of the proposal using wave data obtained from a previous HR Wallingford numerical modelling investigation of the site. The original programme was to test the design to a 1:50 year storm, which was later amended to include a 1:200 year event.

The model tests were carried out in a wave flume as the westerly waves approaching the structure were roughly parallel to the local bathymetry. The revetment was built to cross section drawings and material specifications provided by the Shetland Islands Council.

Measurements of overtopping and uplift forces were carried out to assess the performance of the structure. Analysis showed that wave heights reaching the toe of the structure were depth limited by the bathymetry approximately 0.5km offshore, restricting wave height to around 5.4m Hs.

The observed uplift forces were not great enough to move the slabs, and so they remained stable throughout testing. However, the uplift forces were high enough to cause bending moments in the slabs. Without reinforcement the possibility of stress and fatigue cracks would be likely, therefore it was recommended that reinforcement be included in the slabs.