OPTIMUM METHODS OF TRENCH BACKFILL

TRENCH BACKFILL HAS BECOME AN ECONOMIC FACTOR IN THE DESIGN OF PIPELINES. THIS HAS RESULTED IN THE ACTUAL DESIGN OF TRENCH BACKFILL. IN 1953, THE EAST BAY MUNICIPAL UTILITY DISTRICT, OAKLAND, CALIFORNIA ADOPTED STANDARD SPECIFICATION PROVIDING FOR THE USE OF IMPORTED MATERIAL OR SELECTED MATERIAL FROM THE EXCAVATION AS DIRECTED BY THE ENGINEER FOR TRENCH BACKFILL. THE FOLLOWING YEAR, A SPECIFICATION WAS ADOPTED PROVIDING FOR CLASS I BEDDING FOR PIPE, A CLASS I GRANULAR MATERIAL UP TO THE SPRINGLINE AND SELECTED MATERIAL FROM THE EXCAVATION FROM THE SPRINGLINE TO THE SURFACE. ALL OF THIS MATERIAL WAS COMPACTED TO 80 PERCENT CAL IMPACT, BUT THIS LATTER SPECIFICATION HAS BEEN IMPROVED AND TODAY COMPACTION REQUIRED IS 90-95 PERCENT CAL 216. STANDARD SPECIFICATIONS TODAY FOR TRENCH BACKFILL OF 16-INCH AND SMALLER MORTAR-LINED AND COATED PIPELINES PROVIDE THAT THE BACKFILL MATERIAL PLACED IN THAT PORTION OF THE TRENCH FROM THE GRADE OF THE PIPE TO THE LEVEL OF ONE FOOT ABOVE THE TOP OF THE PIPE SHALL BE APPROVED MATERIAL FROM THE EXCAVATION, OR CLASS III IMPORTED BACKFILL MATERIAL CONFORMING TO THE FOLLOWING REQUIREMENTS: (1) THE MATERIAL MUST BE FREE OF ROOTS, ORGANIC MATTER OR OTHER DELETERIOUS SUBSTANCES, (2) STONES OR LUMPS OF MATERIAL EXCEEDING FOUR INCHES IN GREATEST DIMENSION ARE NOT PERMITTED, (3) THE PLASTICITY INDEX SHALL NOT EXCEED 10, (4) THE PORTION OF THE MATERIAL WHICH PASSES A 200-MESH SIEVE, EXPRESSED AS A PERCENTAGE AND MULTIPLIED BY THE PLASTICITY INDEX, SHALL NOT EXCEED 200, (5) THE PLASTICITY INDEX SHALL BE DETERMINED IN ACCORDANCE WITH THE CURRENT ASTM METHOD D 424, (6) MATERIAL IS BROUGHT UP EVENLY ON EACH SIDE OF THE PIPE AND THOROUGHLY JETTED IN PLACE UNLESS OTHERWISE PROVIDED, AND (7) THE REMAINING PORTION OF THE TRENCH SHALL BE BACKFILLED WITH SELECTED MATERIAL FROM THE EXCAVATION. THE DISTRICT'S STANDARD SPECIFICATIONS FOR TRENCH BACKFILL AND IMPORTED MATERIALS ARE PRESENTED. THEY HAVE BECOME A PART OF ALL CONTRACT DOCUMENTS.

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  • Supplemental Notes:
    • Vol 99, No 6, PP 101-103, 1 FIG, 1 PHOT
  • Authors:
    • Mclean, W R
  • Publication Date: 0

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  • Accession Number: 00232712
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Aug 15 2004 2:44AM