PERFORMANCE OF SUBDRAINS AND SUBDRAIN BACKFILL MATERIALS

During the summer of 1975 the Engineering Materials Office carried out a study of selected subdrains and subdrain backfill materials. Typical subdrain installations throughout the province were selected by Regional staff for investigation. The major objectives of the study were to observe the performance of the installations and to correlate observed performance with the native soil types and backfill materials used. The present Ministry specification for backfill material is fairly restrictive, having been designed as a filter media according to accepted soil mechanics practice to prevent piping and clogging. It was hoped to determine if the actual backfill materials presently used conform to specification and whether the specification could be eased to allow use of a broader range of materials. Nearly all of the installations investigated were functioning well and showed no signs of clogging or piping, although some of the drains had been in place for up to 17 years. Water was flowing freely or there were signs of intermittent flow in most cases. This was true where subdrains were installed as routine design practice in urban areas, as well as when they were used to correct specific drainage problems. The backfill materials used did not always conform to backfill specification, and it appears to be common practice to backfill with granular base or subbase materials employed in other parts of the contract. The native soil types varied over a full range from gravels to heavy clays and the backfill materials varied from sandy gravels to fine sands at or below the fine limit of the Granular "C" gradation. Despite this range of soil types and backfill materials there was no correlation between performance and materials used. It is concluded that present design and construction practices are producing satisfactorily functioning subdrain systems. There is general concensus that the Ministry specification for subdrain backfill should be retained and not extended on the fine side of the gradation to allow the use of material meeting Granular "C" specifications. (Author)

  • Corporate Authors:

    Ontario Ministry of Transportation & Communic, Can

    Engineering Materials Office, 1201 Wilson Avenue
    Downsview, ONo M3M 1J8,   Canada 
  • Authors:
    • MacMaster, J B
  • Publication Date: 1977-6

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: 110 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00335536
  • Record Type: Publication
  • Report/Paper Numbers: EM-7
  • Files: TRIS
  • Created Date: Nov 23 1981 12:00AM