Published on December 30, 2007
EFFECTS OF WOODY DEBRIS ON HIGHWAY STRUCTURES: EFFECTS OF WOODY DEBRIS ON HIGHWAY STRUCTURES Alluvial Fan Seminar Los Angeles, CA May 17, 2005 J. Sterling Jones HEC-18 PIER SCOUR EQUATION: HEC-18 PIER SCOUR EQUATION Slide5: Potential Drift Accumulation at Bridges by Timothy H. Diehl Publication No. FHWA-RD-97-028 . . . . . April, 1997 http://tn.water.usgs.gov/pubs/FHWA-RD-97-028/drfront1.htm Slide6: Drift that accumulates at bridges comes primarily from trees growing on the banks and bank tops of rivers. Floating drift is concentrated along the thread of the stream and moves at about the average flow velocity.. Drift accumulation begins at the water surface, but accretion can cause an accumulation to grow downward to the streambed. Drift damages bridges mostly through local and contraction scour. The recommended method for calculating the depth of drift-related local pier scour is to define an equivalent pier width. Diehl’s Conclusions: Slide7: Maintenance engineers typically know which rivers present drift problems. Channel types with negligible drift delivery might include: (a.)Shallow channels incapable of transporting drift (b.)Deep channels with inundated wooded flood plains to trap floating drift Field studies of drift length and forest characteristics could refine regional estimates of the maximum sturdy-log length which controls the potential for span blockage in wide channels. . Design features appropriate for drift-prone streams include: adequate freeboard, long spans, solid piers, round (rather than square) pier noses, and pier placement away from the path of drift. Diehl’s Conclusions cont’d: Slide8: Diehl’s recommended research on drift : Compilation of existing data from maintenance engineers, bridge files, and damage reports to identify drift-laden rivers and drift-prone bridges. Detailed, three-dimensional measurements of drift accumulations and associated scour in flood conditions. Definition of channel types in which drift delivery is low even in floods. Refinement of maximum sturdy-log length estimates to reflect regional conditions. Identification of bridge design features that promote transport of floating drift for short span bridges. NCHRP Project 12-39Design Specifications for Debris Forces on Highway Bridges: NCHRP Project 12-39 Design Specifications for Debris Forces on Highway Bridges University of Louisville Principal Invest:Arthur C. Parola Completion Date:April 30, 2000 Debris Deflector Ideas: Debris Deflector Ideas Conveyor idea ---Chang brainstorm Vortex Shedding Deflector ---SBIR phase 1 Debris sweeper/bridge sharks/ MOAB’s --- Mike Collier Slide12: Debris Conveyor Idea; Chang 1970’s Slide13: Saunders Slide14: Bridgesharks Best Lab is the Field : Best Lab is the Field AL 1 site (2 Bridgesharks) FL 1 (13) CA 1 (1) IL 2 (12) IN 1 (2) KY ? (31) LA 2 (5) MN 1(2) NC ?? NV 1 (1) OR 1 (1) TN 3 (5) WA 2 (3) WS 1(1) Current Activities: Current Activities NCHRP 24-26 Effects of Debris on Bridge Scour Hydraulic Engineering Circular No. 9 NCHRP Project 24-16 Effects of Debris on Bridge Scour: NCHRP Project 24-16 Effects of Debris on Bridge Scour Contractor: Ayres & Assoc Completion: Dec 2007 NCHRP 24-26 Major Tasks: NCHRP 24-26 Major Tasks Develop guidelines for predicting size and geometry of debris accumulations based on surveys and site reconnaissance Conduct large scale lab experiments Develop guidelines for predicting scour Slide20: U.S. Department Hydraulic Engineering Circular No. 9 of Transportation Federal Highway Administration This Edition Will Include: Culvert Debris Collectors Debris Delivery Debris Forces on Piers Effects on Scour Debris Deflectors Comments/Questions??: Comments/Questions??