Non-Intrusive Bridge Scour Analysis Technique using Laboratory Test Apparatus

Larger and more frequent flood flows expose foundation soils to stronger erosive forces, increasing the likelihood that scour of piers (and abutments) will compromise the structural integrity of some bridges. The development of low-cost, low maintenance, non-destructive methods of bridge scour analysis is therefore becoming ever more important in light of the current economic climate. The use of embedded sensors that measure vibration responses of a structure, due to train loading, may offer potential to track changes in the foundation soil stiffness matrix caused by scour and may inform engineers in implementing appropriate protection schemes. This paper presents a laboratory investigation in which the dynamic response of a scaled pier, installed in a bed of sand and instrumented with an accelerometer, is recorded for a constant and repeatable excitation. Sand stiffness properties were manually altered by increasing the scour depth in progressive experiments. For each experiment, a vibration response was recorded and this was converted to a frequency response using a fast Fourier transform (FFT). Differences between the dynamic signatures of the pier for the different scour conditions investigated were analysed to explore whether this type of non-destructive testing could provide a viable method of detecting scour before the structural integrity of the bridge reaches a critical stage. Results indicate that significantly different frequency responses are recorded for decreasing elevations of bed material around the model pier, indicating that the method may provide the basis for a simple and effective means of monitoring scour around bridge piers.