A major landslide involving about 6 x 10 to the sixth power cubic meter of soft sensitive clay, sand and silt soils occurred on May 16, 1971 in the east bank of the South Nation River about 6 km north of the village of Casselman, Ontario. Aerial photographs and field observations carried out to investigate the sequence of development of this landslide are described in this report. From these studies it was postulated that landslides of this type develop in three distinct stages: Initial rotational slip; retrogressive sliding, termed flowsliding; and, plastic extrusion, termed earthflow. This postulate is supported by analytical studies and correlations with numerous documented landslides. For flowsliding to develop the soil must be sensitive, resulting in flow of the spoil from the crater. For an earthflow to develop in soft to medium stiff clays, an overburden pressure to undrained strength ratio, exceeding 6.0 must exist within the depth of the potential flow. The significance of the earthflow phenomenon is exemplified by the fact the two thirds of the total volume of the 1971 South Nation River land-slide is considered to be a result of earthflow. For purposes of route selection and regional planning, criterion is suggested for evaluating the potential for retrogression by flowsliding or by earthflow in sensitive soils. This criterion is applied to several areas in Ontario and is found to correlate well with field observations and aerial photographs of landslide activity. /Author/

  • Corporate Authors:

    Ontario Ministry of Transportation & Communic, Can

    Research and Development Division, 1201 Wilson Avenue
    Downsview, ONo M3M 1J8,   Canada 
  • Authors:
    • Mitchell, R J
  • Publication Date: 1978-1

Media Info

  • Features: Figures; References; Tables;
  • Pagination: 29 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00174438
  • Record Type: Publication
  • Report/Paper Numbers: Final Rpt.
  • Files: TRIS
  • Created Date: Jun 14 1978 12:00AM