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Hydraulics Engineering


Scour Technology - FHWA Unknown Foundations Summit

To receive a copy of the Summit presentations, please contact Ms. Cynthia Nurmi (contact information to the right)

  • November 15-16, 2005
  • Sheraton Hotel, Lakewood, Colorado

Summit Objectives | Who Should Attend | Format | Background

Summit Objectives

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:

  1. Provide a forum for open discussion/communication on the state-of-the-art techniques available to manage bridges with unknown foundation and of the current standard-of-practice.
  2. Determine capability, reliability and probable cost of state-of-the-art and state-of-the-practice nondestructive methods for determining types, size, structural condition, configuration, and depths of bridge foundation components.
  3. guidance and management strategies based on the outcome of this meeting for state DOTs and other bridge owners. (A council from all parties will be selected to help develop guidelines at a latter date).

Who Attended

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.


  • Brief presentations by select consultants and State DOT personnel on state-of-the-art technologies, methodologies, and management decision making strategies
  • Panel discussions to: 1) identify appropriate guidance for discovering unknown foundations, and 2) define effective strategies for managing unknown foundations and the associated risks.


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.

Updated: 04/07/2011

United States Department of Transportation - Federal Highway Administration