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30 October 2013 York W. Lewis 1 , Alexandra Wayllace 1 , Jonathan W. Godt 2 ,

30 October 2013 York W. Lewis 1 , Alexandra Wayllace 1 , Jonathan W. Godt 2 , Richard M. Wooten 3 , and Ning Lu 1 1 Colorado School of Mines 2 U.S . Geological Survey 3 North Carolina Geological Survey.

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30 October 2013 York W. Lewis 1 , Alexandra Wayllace 1 , Jonathan W. Godt 2 ,

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  1. 30 October 2013 York W. Lewis1, Alexandra Wayllace1, Jonathan W. Godt2, Richard M. Wooten3,and Ning Lu1 1Colorado School of Mines 2U.S. Geological Survey 3North Carolina Geological Survey Hydro-Mechanical Properties and Stability Analysis of Four Landslide-Prone Hillslopes in Western North Carolina

  2. Objectives • Test Hydrological and Geotechnical properties • Calculate Factor of Safety • Determine pore-water pressures needed to cause slope failure. Photos courtesy of NC Geological Survey

  3. Site Locations Mooney Gap Bent Creek Poplar Cove • Slope angles average 31 degrees. Maps courtesy of NC Geological Survey

  4. Typical Soil Horizon Thicknesses 30 cm O A 60 cm B 60 cm C 20 cm Classification: Silty Sands (SM), Silty Clays (SC)

  5. Laboratory Tests • Index Properties for soil classification • Direct Shear (unsaturated & saturated) for shear strength parameters • Transient Release and Imbibition Method (TRIM) for soil-water retention, hydraulic conductivity, and suction stress functions

  6. Test Results Hydraulic Conductivity Function & Soil Water Retention Curve Suction Stress Characteristic Curve & Soil Water Retention Curve

  7. Infinite-Slope Stability Analysis ɸ’ = Effective friction angle (degrees) β = Slope angle (degrees) c’ = Effective cohesion (kPa) ss= Suction stress (kPa) g = Unit Weight (kN/m3) z = Vertical depth (m) (Lu and Godt, WRR, 2008)

  8. Conclusions • Stability calculations indicate modestly stable slopes under field conditions. • Results show that rainfall events need only increase pore water pressures by 6.7 kPa to 13.5 kPa in order to cause landslides in the region. • Use of improved hydrologic/geotechnical testing methods can quantitatively assess regional landslides. Acknowledgement: NASA (Grant # NNX12AO19G)

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