LARGE AGGREGATE SHOTCRETE CHALLENGES STEEL RIBS AS A TUNNEL SUPPORT

LARGE AGGREGATE SHOTCRETE IS THOUGHT TO BE AN ECONOMICAL, RAPID AND EFFECTIVE MEANS OF TUNNEL LINING. SPRAYED ON THE TUNNEL SURFACE CLOSE BEHIND THE EXCAVATION, IT PREVENTS AIR SLAKING OF ROCK. YIELDING ELASTICALLY AT A DECREASING RATE AS IT GAINS STRENGTH, IT PERMITS FORMATION OF A SELF- SUPPORTING ARCH ABOVE THE TUNNEL. A DEVELOPED GROUND ARCH CAN SUBSTANTIALLY REDUCE THE LOAD FOR WHICH A LINING NEED BE DESIGNED. SHOTCRETE EXHIBITS A HIGH ADHESION OR BOND TO THE ROCK. WITH SHOTCRETE A NUMBER OF FEATURES COMBINE TO GIVE THE BEST PRACTICABLE GROUND SUPPORT CONDITIONS: EARLY SUPPORT BY THIN, STRONG FLEXIBLE LINER UNDER CONTINUOUS BLOCKING CONDITIONS, GENERATING AN EFFECTIVE GROUND ARCH AROUND THE OPENING AND AUGMENTING THE SELF-SUPPORTING PROPERTIES OF THE NATIVE GROUND MATERIAL. CONSTRUCTION PROCESSES IN USE ARE THE WET PROCESS AND THE DRY PROCESS. THE TERM WET PROCESS IS USED WHEN ALL MATERIALS ARE MIXED WITH THE REQUIRED WATER OF HYDRATION BEFORE AIR OR PUMP TRANSPORTATION TO THE POINT OF APPLICATION. THIS MIX IS BLOWN INTO PLACE BY AIR PRESSURE AT THE NOZZLE. THE DRY PROCESS CONSISTS OF MIXING ALL MATERIALS,INCLUDING ACCELERATORS, IN A DAMP STATE BEFORE AIR TRANSPORTATION TO THE POINT OF APPLICATION. THE ADDITIONAL WATER IS ADDED AT THE GUN. THE SUCCESSFUL APPLICATION OF SHOTCRETE DEPENDS ON RIGID OBSERVANCE OF THE FOLLOWING RULES: (1) THE DISTANCE BETWEEN THE NOZZLE AND THE POINT OF APPLICATION IS CRITICAL, GENERALLY A DISTANCE OF 3 TO 4 FT., (2) WATER SEEPAGE AREAS AND CONSIDERABLE FLOWS OF WATER CAN BE HANDLED SUCCESSFULLY BY THE PLACING OF A DRAIN PIPE AND PLACEMENT OF SHOTCRETE AROUND IT, (3) SHOTCRETE IMPACTS AT BETWEEN 300 AND 500 FPS WHICH VELOCITIES ARE NECESSARY TO PRODUCE A DENSE, HIGH QUALITY SHOTCRETE, (4) IN ORDER TO KEEP REBOUND, IT IS NECESSARY TO KEEP THE ANGLE OF IMPACT NORMAL TO THE SURFACE, AND (5) NORMAL CONTROL PRACTICE IS TO SPECIFY FABRICATION OF TEST PANELS USING SEVERAL MIXES. GOOD DESIGN USES THE ADVANTAGES OF A NEW MATERIAL COMPLETELY. WITH SHOTCRETE THIS MEANS A TUNNEL SECTION WHICH PRODUCES A MINIMUM OF BENDING MOMENT IN THE SUPPORT. THE SPEED OF APPLICATION OF SHOTCRETE MAY WELL BE THE GREATEST ADVANTAGE.

  • Availability:
  • Supplemental Notes:
    • Vol 39, No 11, PP 51-55, 3 FIG
  • Authors:
    • Sutcliffe, H
    • MCCLURE, C R
  • Publication Date: 1969-11

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Filing Info

  • Accession Number: 00215244
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Feb 9 1970 12:00AM