Johnson Creek Landslide research project, Lincoln County, Oregon : final report to the Oregon Department of Transportation.

Details

• Creators:
  Priest, George R. ; Allan, Jonathan C. ; Niem, Alan R. ; Niem, Wendy A. ; Dickenson, Stephen E.
• Corporate Creators:
  Oregon. Dept. of Transportation. Research Unit
• Corporate Contributors:
  United States. Federal Highway Administration
• Subject/TRT Terms:
  • Landslides
  • Geological events
  • Geotechnical engineering
  • Landslides--Oregon--Lincoln County
  • Geology, Structural--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.
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• Format:
  PDF
• Funding:
  SPR 356
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/21832/dot_21832_DS1.pdf
• File Type:
  [PDF - 34.17 MB]
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha-512:97f46e902820abf706f8d278d1628616d883dc50ec6b6758b8303c0c450c1f246f3aa8d690965b901af7ee200668e4e98c07475f0d4e9ca3acb5aa547acafeff