Monitoring of bridge scour using changes in natural frequency of vibration - a field investigation

The high profile failure of the Malahide Viaduct in late 2009 in Dublin was attributed to erosion of the supporting soils, commonly referred to as foundation scour. This is a more widespread geotechnical structural problem, where foundation scour has been identified as the number one cause of bridge failure in the United States. In light of current changes in climate, increased frequency of flooding, coupled with the increased magnitude of these flood events, leads to a higher risk of bridge failure occurring. Monitoring scour is of significant importance to ensure the continued safe operation of the aging bridge asset network. Most monitoring regimes are based on using expensive underwater instrumentation that is often subject to damage during times of flooding, when scour risk is at its highest. In this paper, a technique based on using dynamic measurements to monitor scour is described. Accelerometers placed on the structure, above the waterline, may be used to detect changes in natural frequency arising from the loss of stiffness due to scour.