Assessment of Scour on Bridge Foundations by Means of in Situ Erosion Evaluation Probe

The work in this paper presents the use of an in situ erosion evaluation probe (ISEEP) to assess scour depth at bridge piers. Numerical modeling and deployment of the device at a North Carolina Outer Banks site damaged by Hurricane Irene in 2011 demonstrates the applicability of the proposed concept. Computational fluid dynamics software, FLOW-3D, was used to assess the scour depth at a bridge pier, and the results were compared with values based on ISEEP-estimated parameters by using an excess-stream power model. The scour depth was also calculated from empirical equations that assumed the same conditions as those used in the numerical analysis. Parametric analysis using FLOW-3D indicated that of the parameters for defining the scour depth, the entrainment coefficient had the largest effect, whereas the drag coefficient had the smallest effect on the scour magnitude within the range of values included in this analysis. The estimated scour depths that were based on ISEEP data agreed relatively well with the scour magnitudes obtained from the numerical analysis, as the ISEEP data reflected the changes in the properties of the sand layer with depth. In contrast, the scour magnitude calculated from the empirical equations underestimated the scour depth, mainly because these equations had no provision for a layered-soil profile. Further validation of both the field-testing procedure and the data reduction approach, including the assessment of the applicability in soils that contain an appreciable percentage of fines, is recommended.