CREEP OF CONCRETE PIPES UNDER LOAD

WHEN 36-IN. (914-MM) DIAMETER CLASS I CONCRETE PIPES WERE BURIED 4 FT. (1.22 M) BELOW THE SURFACE OF A REPRESENTATIVE ROAD CONSISTING OF 4 IN. (102 MM) OF BITUMEN MACADAM ON 9 IN. (230 MM) OF HARDCORE ON 3 IN. (76 MM) OF CLINKER, THE CIRCUMFERENTIAL TENSILE STRAINS MEASURED IN THE PIPES ON COMPLETION OF THE ROAD WERE 33 AND 35 MICROSTRAINS AT THE TOP AND BOTTOM RESPECTIVELY. THESE STRAINS INCREASED BY ABOUT 40 MICROSTRAINS AT THE TOP OF THE PIPE AND BY 30 MICROSTRAINS AT THE BOTTOM DURING THE NEXT SEVEN WEEKS DURING WHICH THE ROAD WAS NOT OPEN TO TRAFFIC. DURING THE SEVEN WEEKS, NO CHANGE OCCURRED IN THE STRAINS RECORDED IN 12-IN. (305-MM) GLAZED VITREOUS CLAY PIPES OR IN 36-IN. (914-MM) CAST IRON PIPES BURIED TO THE SAME DEPTH BELOW THE ROAD. ALTHOUGH IT SEEMED CERTAIN THAT CREEP OF THE CONCRETE PIPES UNDER THE BACKFILL LOADING COULD ACCOUNT FOR SOME INCREASE IN THE CIRCUMFERENTIAL STRAIN, IT WAS THOUGHT THAT THE LARGE INCREASES RECORDED THREW DOUBT ON THE READINGS. AN EXPERIMENT HAS NOW BEEN MADE TO DETERMINE THE MAGNITUDE OF THE CREEP OCCURRING IN A CONCRETE PIPE UNDER PROLONGED LOADING AND TO SEE WHETHER IT IS AFFECTED BY THE AGE OF THE CONCRETE WHEN THE PIPE IS LOADED. IN THESE TESTS, TWO 36-IN. (914-MM) CONCRETE PIPE RINGS WERE LOADED WHEN THE CONCRETE WAS SEVEN MONTHS OLD. LOADS OF 600 LB. (272 KG) WERE APPLIED TO EACH RING AND HELD CONSTANT FOR 6 MONTHS. WITH THE RINGS LOADED WHEN THE CONCRETE WAS A MONTH OLD, THE CREEP STRAIN RESULTING FROM SIX MONTHS OF LOADING WAS 56 MICROSTRAINS AND THUS WAS 2.8 TIMES THE CLASTIC STRAIN OF 20 MICROSTRAINS RESULTING FROM INITIAL APPLICATION OF LOAD. WITH THE RINGS LOADED WHEN THE CONCRETE WAS SEVEN MONTHS OLD, THE CREEP STRAIN RESULTING FROM SIX MONTHS OF LOADING WAS 15 MICROSTRAINS AND THUS APPROXIMATELY EQUAL TO THE INITIAL ELASTIC STRAIN OF 16 MICROSTRAINS. THE INITIAL ELASTIC STRAINS WERE, THEREFORE, SMALLER THAN THOSE MEASURED IN THE PIPES UNDER THE ROAD, BUT THE CREEP STRAINS IN THE RINGS LOADED WHEN THE CONCRETE WAS A MONTH OLD WERE LARGER THAN THOSE RECORDED IN THE ROAD. THE RESULTS OF THE TESTS ON THE PIPE RINGS THUS SUPPORT THOSE OBTAINED IN THE EARLIER ROAD EXPERIMENTS. THEY EMPHASIZE THAT CONCRETE PIPES SHOULD NOT BE USED FOR INSTRUMENTAL PURPOSES WHEN STUDYING THE INCREASE OF BACKFILL PRESSURE UNDER A ROAD. SUCH TESTS ARE BEST DONE WITH METAL PIPES WHICH DO NOT EXHIBIT CREEP UNDER LOAD. /RRL/A/

  • Supplemental Notes:
    • Rrl Rept No 247, 10 PP, 2 FIG, 3 TAB, 1 REF
  • Corporate Authors:

    MINISTRY OF TRANSPORT, LONDON (UK)

    ,    
  • Authors:
    • Grainger, J W
  • Publication Date: 1969

Subject/Index Terms

Filing Info

  • Accession Number: 00216581
  • Record Type: Publication
  • Source Agency: Road Research Laboratory /UK
  • Files: TRIS, ATRI
  • Created Date: Apr 20 1970 12:00AM