Scour at Bridge Foundations on Rock

Current methodology for scour prediction around bridge foundations considers rock as either "erodible" or "non-erodible." Equations for scour in sand are used to predict the scour depth in erodible rock. As a consequence, predictions of scour in rock frequently overestimate the extent and depth of scour so that founding elevations for piers and abutments on rock are established at levels that require very expensive and difficult excavation. Some rock types degrade very rapidly to produce a highly erodible combination of soil and rock fragments (e.g., compacted shales absorb moisture, swell, and disintegrate). Available scour prediction methods do not permit differentiation among rock types that behave in fundamentally different ways. Scour in fractured or degradable rock is affected by the properties of intact pieces of rock, as well as by the discontinuities in the rock strata. Hydrodynamic forces caused by highly turbulent flow around bridge piers and abutments may remove weakened layers to expose relatively intact rock. These new surfaces may deteriorate in-between flow events and then be susceptible to erosion during the next flood event. Other rock types decompose very slowly so that during the design life of a bridge, intact pieces of rock remain essentially unaltered. Scour in such rock types takes place by plucking, dislodgment, and displacement of rock fragments, especially when large pressure differences are generated around piers and abutments. An improved methodology for estimating the rate and design depth of scour in rock over the service life of a bridge is needed. Guidelines that address design issues as well as site-investigation sampling and testing protocols are needed to assist practitioners in applying the methodology. Also, construction guidelines are needed to promote practices that minimize the potential for scour in rock. The objectives of this research are to develop: (a) a methodology for estimating the time rate of scour and the design scour depth of a bridge foundation on rock, and (b) design and construction guidelines for application of the methodology.


  • English


  • Status: Completed
  • Contract Numbers:

    Project 24-29

  • Sponsor Organizations:

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590

    American Association of State Highway & Transportation Officials

    444 North Capitol Street, NW, Suite 225
    Washington, DC  United States  20001

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001
  • Project Managers:

    Reynaud, David

  • Performing Organizations:

    MACTEC Engineering and Consulting, Incorporated

    12104 Indian Creek Court, Suite A
    Beltsville, MD  United States  20705-1242
  • Principal Investigators:

    Keaton, Jeffrey

  • Start Date: 20060822
  • Expected Completion Date: 0
  • Actual Completion Date: 20110731
  • Source Data: RiP Project 12200

Subject/Index Terms

Filing Info

  • Accession Number: 01549305
  • Record Type: Research project
  • Source Agency: National Cooperative Highway Research Program
  • Contract Numbers: Project 24-29
  • Files: RiP
  • Created Date: Dec 31 2014 1:01AM