A Methodology for Determining Scour Depth around Structures in Gravel-bed Rivers

Scour is the result of the erosive action of flowing water, entraining and removing boundary material from channel beds and/or banks and around bridge foundations. In gravel-bed rivers the interaction of the heterogeneous, large gravel particles with the approaching flow can generate coherent turbulent structures in the flow. In addition to increasing the shear stress applied by the flow onto the bed, these structures create a highly variable bed shear stress field increasing the gravel-bed mobility (Tsakiris et al., 2014; Sarkar et al., 2016), compromising bridge foundation integrity. The majority of the formulas used in current engineering practice for predicting scour depth around bridge foundations have been developed for sand-bed rivers, which are characterized by near-uniform bed material (Dey and Raikar, 2005; Ettema et al., 2011; Guo et al., 2012; Manes and Brocchini, 2015). As a result, parameters such as the heterogeneity of bed material have been excluded from their formulations, and the empirical coefficients appearing in these formulas have been derived from laboratory experiments conducted with near uniform sand-sized sediment. Due to these limitations, when applied in gravel-bed rivers, these formulas significantly overestimate the scour depth (Dey and Raikar, 2005; Holnbeck, 2011). Recognizing the shortcomings of current scour prediction methodologies, researchers have attempted to include the effects of gravel particle heterogeneity using empirically derived correction coefficients. However, the failure of existing scour prediction methodologies to fundamentally account for the unique characteristics of gravel-bed rivers translates to significant scour depth prediction errors, even after correction.   Development of a scour prediction methodology that accounts for gravel-bed rivers will be valuable for bridge owners and practicing engineers and will provide more accurate predictions of the scour depth. The objective of this research is to develop a rigorously tested and rapidly deployable methodology for bridge owners that will accurately predict scour at new bridge foundations and evaluate scour at existing bridge foundations in gravel-bed rivers by (1) providing reliable data for fluid-induced forces, required to generate incipient motion in the surface and subsurface layers of gravel-bed rivers; and (2) combining fluid-induced erosion forces, and incipient motion data to predict scour depths at bridge foundations with gravel-bed rivers that have ¼ inch gravel to 12 inch cobble mixtures with varying sand content up to 20%.  

Language

  • English

Project

  • Status: Proposed
  • Funding: $600000
  • Contract Numbers:

    Project 24-28

  • Sponsor Organizations:

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001

    American Association of State Highway and Transportation Officials (AASHTO)

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

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Project Managers:

    Crichton-Sumners, C

  • Start Date: 20171219
  • Expected Completion Date: 0
  • Actual Completion Date: 0
  • Source Data: RiP Project 41650

Subject/Index Terms

Filing Info

  • Accession Number: 01634968
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 24-28
  • Files: TRB, RiP
  • Created Date: May 19 2017 1:00AM