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Mechanisms and kinematics of three translational slides along the North Saskatchewan River Valley, Edmonton
 

Mechanisms and kinematics of three translational slides along the North Saskatchewan River Valley, Edmonton

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    Mechanisms and kinematics of three translational slides along the North Saskatchewan River Valley, Edmonton Mechanisms and kinematics of three translational slides along the North Saskatchewan River Valley, Edmonton Presentation Transcript

    • K. W. Soe Moe, BGC Engineering Inc. D.M. Cruden, C.D. Martin, University of Alberta D. Lewycky, P. R. Lach, The City of Edmonton Mechanisms and kinematics of three translational slides along the North Saskatchewan River Valley, Edmonton
    • Edmonton Landslides Keillor Road 2003 Whitemud Road 1999 Forest Heights 1900s
      • In Alberta, many of the river valleys are post-glacial
      • The valley walls are often steep
      • Large landslides and slow slope movements affect many of the valley walls
      • Long term slope movements
      • Delayed failures
    • Road Sign
    • Road Sign
    • KEILLOR ROAD LANDSLIDE (FALL 2002)
      • Started as a minor toe failure in 1989
      • Movement progressed upslope in 1994
      • In 1997, an 8 to 15 m deep cast-in-place tangent pile retaining wall was constructed
      • A crack was observed across the roadway in August 2001
      • A major failure occurred in the fall of 2002
      • From 2002 to 2005
        • 11 m slope retrogression
        • Toe moved 30 m into the river
    • History Keillor Road Landslide
    • Pre-failure Slope Profile (1990)
    • Post-Failure Slope Profile (2003)
    • Post-Failure Slope Profile (2004)
    • Field observation of slope movements September 2001 July 2003 Keillor Road settlement
    • Movements of lower trail pile wall May 2003 June 2004
    • Field measurements of piezometric pressure
      • A perched water table was located in till layer
      • Standpipes were dry after installation in the bedrock
      • Piezometric readings from the bedrock were well below the hydrostatic pressure
      • Piezometers installed below the displaced material showed a reduction in pore pressure with time due to dilation of the bedrock
      Pore pressure distribution in the slide area
    • Horizontal displacement of crack meters Average movement of the slide body Horizontal displacement of crack meters Location 2003 (mm/month) 2004 (mm/month) Main scarp 125 250 Graben 250 500 Toe 350 850
    • Whitemud Road Landslide, October 23, 1999
    • Whitemud Road Landslide
      • Oct 23, 1999, 270 m section along Whitemud Road
      • Damaged 7 residential lots
      • Resulted vertical drop of 18 m
      • Major movements took place in a single day
    • Whitemud Road Landslide
    • Landslide history
      • In 1967, a failure occurred 300 m downstream
      • In 1976, a second failure occurred just north of the1967 failure
      • From 1997 to 1999, displaced trees at the river level as well as significant debris and tree accumulation are visible in airphotos.
    • Landslide stages Development of main scarp
    • Landslide stages Development of a counter scarp
    • Landslide stages Major failure due to downward movement of the active block
    • Pre and Post Failure Cross-Section
      • Graben - the displaced material was completely disturbed. The drilling records revealed that the till layer is missing and the sand is directly in contact with the bedrock
      • Main body - the displaced material was less disturbed and intact soil and bedrock strata were noted from the drill hole
    • FOREST HEIGHTS PARK LANDSLIDE (EARLY 1900S)
      • Slope instability dated back to the early 1900’s when coal mining was conducted in the area
      • Park, 1000m long, 150 m valley, with slope angle ranged from 10 to 40°
      • Continued slope movements after toe berm construction in 1980s
      • Steep scarps, grabens, cracks occupy the valley wall
      River valley view of Forest Height Park (2004)
    • POST-FAILURE LANDSLIDE MECHANISM
      • Rate of movements controlled by the groundwater level in the cracks
      • Downward movement of the displaced material inside the graben contributed to retrogression of the slope crest (3 to 4 m from 1980 to 2002)
    • Conclusions
      • Landslides in Edmonton’s river valleys - a translational movement along a bentonite layer
      • Pre-failure slope movements - minor failures at the toe and the mid-slope area
      • A distinct graben feature appears at the head of the displaced material
      • Stability analysis consideration
      • After a major failure, displaced material rests on the rupture surface and the factor of safety improve with the new slope configuration.
      • Post-failure movements
        • Increase in groundwater level
        • Changes in slope configuration
        • Loading at the slope crest
    • Thank you