Details:

• Creators:
  Priest, George R. ; Allan, Jonathan C. ; Niem, Alan R. ; Niem, Wendy A. ; Dickenson, Stephen E.

  Priest, George R. ; Allan, Jonathan C. ; Niem, Alan R. ; Niem, Wendy A. ; Dickenson, Stephen E. Less -
• Corporate Creators:
  Oregon. Dept. of Transportation. Research Unit
• Corporate Contributors:
  United States. Federal Highway Administration
• Subject/TRT Terms:
  [+]

  Geological Events Geology, Structural--Oregon--Lincoln County. Geotechnical Engineering Landslides Landslides--Oregon--Lincoln County
• Publication/ Report Number:
  FHWA-OR-RD-08-13
• Resource Type:
  Tech Report
• Geographical Coverage:
  Oregon
• Edition:
  Final report.
• Corporate Publisher:
  Oregon. Dept. of Geology and Mineral Industries
• Abstract:
  A five-year study indicates that the Johnson Creek landslide moves in response to intense rainfall that raises pore water
  
  pressure throughout the slide in the form of pulses of water pressure traveling from the headwall graben down the axis of
  
  the slide at rates of 1.4 to 2.5 m/hr in the upper part and 3.5 m/hr to virtually instantaneous in the middle part. Vertical
  
  arrays of piezometers measured infiltration at rates of only 50 mm/hr, so infiltration is too slow to affect saturated water
  
  pressure except in the headwall graben. The hydraulic gradient through the slide mass is small and groundwater flow
  
  appears to be nearly horizontal, roughly parallel to the slide plane. These observations and the rapidity of pressure
  
  transmission are consistent with a high effective hydraulic conductivity throughout the slide mass. Westward slope of the
  
  piezometric surface is consistent with better drainage in the western part of the slide. Movement episodes proceed by en
  
  masse movement when threshold pore pressures are reached followed by faster and faster movement of the middle portion
  
  of the slide when pore water pressure there rises above ~9.4 to 10.8 m head above the slide plane. In January 2003, slide
  
  velocity increased by an order of magnitude when head above the slide plane at the middle observation site reached 11.4 m
  
  while the western site reached ~9 m, ~2 m above its maximum for the following four winter seasons. Antecedent rainfall
  
  correlating with this accelerated movement was mean precipitation of 0.84 m in the previous 60 days and 2.1 mm/hr in the
  
  62 hours immediately before the movement. Antecedent deformation correlating with the accelerated movement was
  
  extension of 1 cm in the lower part of the slide, possibly raising effective hydraulic conductivity there. This increased
  
  hydraulic conductivity may have caused a uniquely rapid pore pressure response in the lower part of the side and the unique
  
  2-m increase in head. With respect to engineering solutions for slide mitigation, the reduction of water pressures at the
  
  headwall graben by dewatering (e.g., drains or pumps) should be effective given the inferred high hydraulic conductivity of
  
  the slide and sensitivity to pressure change at the graben. Limit equilibrium stability analyses indicate that 3 m of erosion
  
  would destabilize the slide for most of the winter season. This finding suggests that buttressing the toe of the slide is an
  
  effective long-term remediation option.
  
  
• Format:
  PDF
• Funding:
  SPR 356
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  [+]

  urn:sha256:59aaadac5a37947d4e2d50e9330b82ac9c5b063b74f60a2ac7e745f1f6a8dd28
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/21832/dot_21832_DS1.pdf
• File Type:
  [PDF-34.17 MB]