NAST TUNNEL EXCAVATION HISTORY

NAST TUNNEL IS THE FIRST GRANITIC ROCK TUNNEL TO BE EXCAVATED BY A MACHINE FOR THE U.S. BUREAU OF RECLAMATION. THE MACHINE HAS EXCAVATED 7500 FT OF THE TUNNEL AT THIS WRITING. THERE HAVE BEEN A FEW GOOD PERFORMANCES; 31 FT IN 1, 8 HR SHIFT, AND 75 FT IN A 24 HR PERIOD, BUT GENERALLY, PROGRESS HAS BEEN SLOWER THAN THAT ACCOMPLISHED IN THE AREA WITH REASONABLE COMPARABLE CONDITIONS USING CONVENTIONAL EXCAVATION TECHNIQUES. BUTTON CUTTERS, NOW EMPLOYED USING COMPRESSION AS THE MEANS OF FRACTURING THE ROCK, GIVES AN AVERAGE CUTTING RATE OF 3 FT PER HR. DISC CUTTERS MANUFACTURED BY THE MACHINE BUILDERS WERE TRIED BRIEFLY BUT THE SNAP RINGS HOLDING THE DISCS TO THE HUB FAILED. HOWEVER, DISC CUTTING RATES OF 6 FT PER HR WERE RECORDED FOR SHORT PERIODS OF TIME IN A COMPETENT COARSE GRAINED PORPHYRITIC GRANITE. THE MUCK WAS ALSO CONSIDERABLY LARGER AND MORE EASILY HANDLED THAN THAT PRODUCED BY THE BUTTON CUTTERS. HUGHES TOOL CO. IS WORKING ON A DISC TYPE CUTTER AND EXPECTS TO HAVE THEM ON THE CUTTERHEAD BY MID JUNE. /AUTHOR/

Media Info

  • Features: Figures;
  • Pagination: p. 1137-47
  • Serial:
    • Volume: 2

Subject/Index Terms

Filing Info

  • Accession Number: 00236582
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Feb 27 1974 12:00AM