This paper summarizes the findings of two recently completed NCHRP research studies to determine the depths and conditions of unknown bridge substructures for scour safety investigations. The NCHRP 21-5 and 21-5(2) studies were focused on the determination of unknown bridge foundation depths and other information related to scour safety studies. Over 100,000 bridges have unknown foundation conditions out of the total National Bridge Inventory of almost 500,000 bridges. The study involved research on surface and borehole methods including stress wave, vibration, magnetic and radar NDE methods. Of these, the borehole Parallel Seismic and surface Ultraseismic methods were found to have the broadest application for determining unknown depths of bridge substructures. The paper explains the two methods. Research case history results are also presented to illustrate data analysis.
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