NDT of Unknown Bridge Foundations for Louisiana DOTD

From 2008-2015, FDH completed over 2,000 scour evaluations for bridges with unknown foundations. The first phase of scour analysis included the qualitative assessment of a bridge’s susceptibility to scour using aerial photos, bridge inspection records, pile records, watershed characteristics, channel/river platform features, and other factors in accordance with the Federal Highway Administration’s (FHWA) two hydraulic engineering circular guidelines, HEC-20 and HEC-18. Phase 2 scour susceptibility evaluations of over 500 bridges deemed scour susceptible at the conclusion of the Phase 1 analyses. This included detailed hydraulic modeling of the river and bridge section using the US Army Corp of Engineers’ Hydrologic Engineer Center’s River Analysis System (HEC-RAS), followed by scour analysis utilizing the procedures outlined in HEC-18, “Evaluating Scour at Bridges.”

From 2002-2013, FDH performed foundation mapping of over 1,800 existing bridge piles using Dispersive Wave testing and Dispersive Side Sonic testing to determine the unknown lengths of existing bridge piles for timber, steel, and concrete bridge types.

In 2002, FDH performed nondestructive tests to validate its testing methods and determined the unknown lengths of existing bridge piles and foundation sizes for 100 timber and concrete bridge types, as a comparison of known lengths provided by Louisiana DOTD. This program confirmed the accuracy of the Dispersive Wave test method.

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