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Scour Technology - FHWA Unknown Foundations Summit
To receive a copy of the Summit presentations, please contact Ms. Cynthia Nurmi (contact information to the right)
The Unknown Foundations Summit brought together individuals with in-depth knowledge, experience, and an interest in identifying appropriate applications and limitations of state-of-the-practice and state-of-the-art technologies for characterizing unknown foundations, as well as strategies for managing unknown foundations and all associated risks.
The objectives of the summit were to:
Bridge owners, technology practitioners, university researchers, consultants, and vendors of nondestructive evaluation methods; State DOT personnel who have applied various methods for unknown foundations; State DOT personnel who are involved in the management of bridges with unknown foundations; and FHWA personnel responsible for facilitating the technology transfer and development of guidelines.
There are approximately 500,000 roadway bridges over waterways in the United States. For many of these structures, "as built" information is not unavailable. Consequently, over 80,000 bridges have been identified as having unknown foundations according to the National Bridge Inventory (NBI). Not having foundation information exposes bridge owners and the public to unnecessary risk, congestion, and cost as relatively uninformed decisions are made to prioritize and plan bridge repairs, upgrades, or replacements.
Characterizing the type, size, depth, configuration, materials, and structure conditions of unknown foundations is essential for (1) scour concerns, (2) structural upgrade/replacements, and (3) seismic retrofitting. Identifying the type and condition of existing foundations is essential for determining structure repair or upgrade strategies that will effectively reduce safety risks, construction time, and costs. Furthermore because the number of bridges with unknown foundations is so large, developing effective strategies for managing and characterizing unknown foundations in a practical, economical, and nondestructive manner is critical for realizing these benefits.
In the last decade, several nondestructive techniques have been developed, modified and tested at various sites to evaluate the type, size, depth, configuration, and condition of unknown foundations. Destructive methods such as probing, drilling or digging alongside foundation elements and non-destructive test technologies (NDT) such as seismic, electrical, magnetic, and radar have been evaluated. The actual type of NDT method chosen has been project specific depending on access, foundation configuration, nature of subsurface soils, and the skills and equipment of the practitioner, etc. NDT methods are cautiously evolving and interpretation is still somewhat subjective based on the interpreter's judgment and experience. Few DOT's and other bridge owner agencies (Forest Service, Park Service, etc.) have conducted evaluation of their unknown foundations in accordance with FHWA guidance.