MECHANICS OF LOCAL SCOUR

THE BASIC MECHANISM OF LOCAL SCOUR, I.E., SCOUR DUE TO THE PIER ALONE IS STUDIED. IT HAS BEEN SHOWN THAT THE MECHANISM OF SCOUR AT A BLUNT NOSED PIER IS THE STRONG HORSESHOE VORTEX SYSTEM UPSTREAM OF A BLUNT NOSED PIER. THE MECHANISM WHICH FORMS THE HORSESHOE VORTEX IS THE PRESSURE FIELD INDUCED BY THE PIER. WHEN THE PRESSURE FIELD IS STRONG ENOUGH THE COMING FLOW BOUNDARY LAYER SEPARATES AHEAD OF THE PIER AND ROLLS UP TO FORM THE HORSESHOE VORTEX. PIERS AT WHICH THE HORSESHOE VORTEX SYSTEM DOES NOT FORM ARE CALLED SHARP NOSED. MAXIMUM SCOUR OCCURS AT THE UPSTREAM END OF A BLUNT NOSED PIER. THIS STUDY IS LIMITED TO BLUNT NOSED PIERS . THE MAGNITUDE OF MAXIMUM SCOUR IS INVESTIGATED ANALYTICALLY USING THE MOMENTUM PRINCIPLE, BY ATTEMPTING TO INTEGRATE THE NAVIER-STOKES EQUATION IN THE BOUNDARY LAYER IN THE SCOUR HOLE, AND BY TRYING TO SPECIFY THE RELATION BETWEEN THE STRENGTH OF THE HORSESHOE VORTEX AND LOCAL SCOUR . THIS STUDY HAS DEMONSTRATED THE EXISTENCE OF A BASIC FUNCTION BETWEEN SCOUR DEPTH AND THE PIER REYNOLDS NUMBER. FOR SANDS WHOSE MEDIAN DIAMETER IS LESS THAN 0.52MM, IT APPEARS THAT SCOUR DEPTH IS INDEPENDENT OF SEDIMENT SIZE. WHEN THE SEDIMENT SIZE IS LARGER, SCOUR DEPTH DECREASES AS THE SEDIMENT SIZE INCREASES FOR THE SAME HYDRAULIC CONDITIONS. THE TIME REQUIRED TO REACH 75 PERCENT OF THE MAXIMUM SCOUR DEPTH IS A FUNCTION OF THE APPROACH FLOW VELOCITY. LABORATORY STUDIES INDICATE THAT UP TO VELOCITIES OF 6 FPS, SUCH TIME WILL PROBABLY BE LESS THAN 100 MINUTES.

• Supplemental Notes:
  • Cer66hws22, 57 PP, 31 FIG, 12 PHOT, 58 REF
• Corporate Authors:

  Colorado State University, Fort Collins

  Engineering Research Center
  Fort Collins, CO  United States  80523
• Authors:
  • Shen, H W
  • Schneider, V R
  • Karaki, S S
• Publication Date: 1966-6

Subject/Index Terms

• TRT Terms: Analysis; Equations; Flow; Force; Friction factor; Mechanics; Momentum; Piers (Supports); Piers (Wharves); Reynolds number; Scour; Sediments; Size; Spheres; Studies; Systems; Velocity; Vortices
• Uncontrolled Terms: Principles
• Old TRIS Terms: Blunt bodies; Pressure area; Stokes law; Study analysis
• Subject Areas: Bridges and other structures; Highways;

Filing Info

• Accession Number: 00208350
• Record Type: Publication
• Files: TRIS
• Created Date: Sep 27 1994 12:00AM