INVESTIGATION OF FLEXIBLE MATS TO REDUCE SCOUR AROUND BRIDGE PIERS

EXPERIMENTS TO INVESTIGATE THE POSSIBILITY OF PROTECTING BRIDGE PIERS IN ERODIBLE MATERIAL BY MEANS OF FLEXIBLE MATS PLACED AROUND THE PIERS WERE MADE BY THE ROCKY MOUNTAIN HYDRAULIC LABORATORY IN COOPERATION WITH THE UNITED STATES BUREAU OF PUBLIC ROADS. THE BED WAS OF NONCOHESIVE MATERIAL AND OBSERVATIONS WERE MADE UNDER BOTH EQUILIBRIUM AND DEGRADING CONDITIONS. IT WAS FOUND THAT THE TWO GREATEST HAZARDS TO THE EFFECTIVE FUNCTIONING OF SUCH MATS WERE (1) THE TENDENCY OF UPWARD CURRENTS TO MOVE MATERIAL UP THROUGH THE MAT, AND (2) THE TENDENCY OF THE MAT TO BRIDGE OR BUCKLE DUE TO BOTTOM IRREGULARITIES, THUS OPENING UP UNDERCHANNELS THROUGH WHICH BED MATERIAL IS EASILY TRANSPORTED AWAY. IT IS IMPRACTICAL TO SEAL OFF THE UNDERFLOW WITH AN IMPERVIOUS MAT BECAUSE THE GREATEST PRESSURE OCCURS NEXT TO THE PIER WHERE WATER-TIGHTNESS WOULD BE DIFFICULT TO ATTAIN, AND BECAUSE THE MAT WOULD HAVE TO BE EXTREMELY THICK TO SEAL OFF POSSIBLE UPWARD FLOW BY SHEER WEIGHT. THE BEST PROTECTION WAS AFFORDED BY A HEAVY, COMPLETELY FLEXIBLE MAT WITH COMPARATIVELY SMALL OPENINGS. PROTOTYPE CONSTRUCTION OF SUCH A MAT COULD BE FROM WORN CHAINS, WHICH WITH HOT-DIP GALVANIZING SHOULD HAVE LONG LIFE. PLACING GRAVEL UNDER THE MAT AT THE TIME OF INSTALLATION GREATLY IMPROVED ITS EFFECTIVENESS. THE COMBINATION, WHICH APPARENTLY FUNCTIONED AS AN INVERTED FILTER IN PREVENTING BED MATERIAL FROM BEING CARRIED UP THROUGH THE MAT, PROVIDED COMPLETE PROTECTION AGAINST LOCAL SCOUR AROUND THE PIER UNTIL THE BED OF THE ENTIRE STREAM HAD DEGRADED TO SUCH A LOW ELEVATION THAT THE CHAIN MAT WAS NO LONGER ABLE TO FOLLOW THE BED DOWN AROUND ITS PERIPHERY. A FULL-SCALE TEST WAS RECOMMENDED, WITH LATER SYSTEMATIC INVESTIGATION OF THE PROPER NET DIAMETER IF PROTOTYPE RESULTS SHOW POSSIBILITIES OF ECONOMICAL AND EFFECTIVE FUNCTIONING.

Media Info

  • Media Type: Print
  • Features: Appendices; Figures; References; Tables;
  • Pagination: pp 12-22
  • Monograph Title: Scour around bridges
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00204418
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: May 22 1972 12:00AM