SYNTHESIS OF RECENT TRENCH BACKFILLING STUDIES

FOR THE PAST 12 YEARS THE MINNESOTA DEPARTMENT OF HIGHWAYS HAS BEEN STUDYING THE SETTLEMENT OF SLIT-TYPE TRENCHES BACKFILLED WITH THE SAME SOIL REMOVED FROM THEM. IN THE FIRST TWO PHASES VARIOUS TYPES OF COMPACTORS AND SOIL TYPES WERE USED. IN THE THIRD PHASE 17 TRENCHES WERE DUG IN ONE TYPE OF SOIL AND THE SETTLEMENT WAS OBSERVED UNDER VARIOUS DEPTHS WERE OBSERVED IN ADDITION TO SURFACE SETTLEMENTS. IT WAS FOUND THAT ESSENTIALLY NONE OF THIS SETTLEMENT OCCURRED BELOW THE BOTTOM OF THE TRENCH. IT WAS CONCLUDED THAT APPROXIMATELY 1/2 TO 1 IN. OF SETTLEMENT MUST BE EXPECTED FOR TRENCHES IN PLASTIC SOILS EVEN WHEN COMPACTED TO A RELATIVELY HIGH DENSITY. THE PURPOSE OF THIS SYNTHESIS PROJECT HAS BEEN TO PUT TOGETHER ALL OF THE DATA FROM THE PREVIOUS TRENCH STUDIES. IT IS SHOWN THAT FOR EACH SOIL TYPE THERE IS AN ADVANTAGE TO COMPACTING TO GREATER THAN A 95 PERCENT LEVEL, BUT EVEN AT THIS LEVEL SETTLEMENT OF 0.5 IN. WILL OCCUR. HOWEVER, IF A COMPACTION LEVEL LESS THAN 90 PERCENT IS ATTAINED, SETTLEMENTS OF ABOUT 1.5 IN. CAN BE EXPECTED MORE THEN 50 PERCENT OF THE TIME. A TABLE SHOWS THE SETTLEMENTS TO BE EXPECTED FOR THE VARIOUS SOIL TYPES AND COMPACTION LEVELS AND ANOTHER TABLE SHOWS THE COMPACTION PROCEDURES WHICH RESULTED IN THESE COMPACTION LEVELS FOR THE MINNESOTA STUDIES. IT IS EMPHASIZED THAT MOISTURE CONTENT AND OTHER CONDITIONS SUCH AS THE EFFICIENCY OF THE COMPACTORS MUST BE CONTROLLED ON THE JOB TO RESULT IN THE LEVELS OF COMPACTION SPECIFIED.

  • Supplemental Notes:
    • INVESTIGATION NO 663
  • Corporate Authors:

    University of Minnesota, Minneapolis

    Department of Civil and Mineral Engineering, 122 Civil and Mineral Engineering Building
    Minneapolis, MN  USA  55455-0220
  • Authors:
    • Skok, E L
  • Publication Date: 1972-9

Media Info

  • Pagination: 64 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00214550
  • Record Type: Publication
  • Source Agency: Federal Highway Administration
  • Report/Paper Numbers: Final Rept
  • Files: TRIS, USDOT
  • Created Date: Apr 27 1974 12:00AM