Landslides Mass Wasting

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Landslides / Mass Wasting
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From My Homeowners Policy(Why this is so
important)
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Mass Wasting

• Any downslope movement of rock and soil under the
  influence of gravity.
• "Landslide"
• "Rockslide" "Creep" "Rock Fall"

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Landslide Anatomy
Landslide sketch from the West Virginia
Geological Survey
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Important Landslide Facts

• Most are very slow (inches per year)
• Most occur naturally
• Homeowners insurance does not pay.

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Landslide Geography

• Steep Slopes
• Slide-Prone Soils
• High Precipitation
• National Landslide Overview Map

(connect)
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Slide-Prone Area Map
Slide-prone area map by Peter Lessing, West
Virginia Geological Survey
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Angle of Repose

• The maximum slope at which loose, cohesionless
  material is stable

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Angle of Repose Determined By

• Particle size
• (higher for large particles)
• Particle shape
• (higher for angular shapes)
• Shear strength
• (higher for high shear strength)

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Upsetting Stability

• Increase the slope
• Decrease the shear strength
• Increase the effect of gravity

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Landslide Triggers
Removal of Support
Excavation
Erosion
Rainfall, Snowmelt
Water disposal, Improper grading
Addition of Moisture
Removal of Vegetation
Forest fires
Timbering
Volcanic ash, Landslides, Snow
Placement of fill
Addition of Weight
(Used like "removal of support")
Grading fill steeper than its repose angle
Oversteepening
Earthquakes, Thunder
Blasting, Heavy equipment
Vibrations
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Landslide Considerations
Risk starts at only 15o
Gradient
Clay soils / shale bedrock are the worst
Soil / Bedrock
Moisture
Pore pressure, Lubrication, Weight
Vegetation
Roots anchor soil, remove water
Support
Must be maintained
Weight
Drives the slide, compression of substrate
Vibrations
Result in a loss of friction
Exceeding the angle of repose
Oversteepening
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Types of Landslides
Rock and soil moving as a unit over a curved
failure surface.
Slump Rotational Slide
Similar to a slump, but the material breaks-up
and flows.
Earthflow
Much higher moisture content than an earthflow
- the material makes a "batter" with water.
Mudflow Debris Flow / Avalanche
Rock Slide Block Glide
A block of bedrock sliding down dip.
Creep
Gradual downslope movement of rock and soil.
Complex Landslide
A combination of two different slide types.
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Recognizing Problem Areas

• Curved trees
• Stuck windows
• Stuck doors
• Leaning walls
• Plaster cracks
• Foundation cracks
• Damaged chimneys
• Leaning poles
• Scarps
• Toes
• Seeps
• Pavement damage

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Before buying on a hillside

• Be suspicious!
• Check target and adjacent properties
• Some problems can be fixed
• Fixes are temporary and expensive
• Get expert advice
• Soil Conservation Service /
• Geological Survey

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Landslide Stabilization

• Your efforts will be temporary!
• Calculate or contribute to the moving mass!
• Support the base
• Anchor through slip plane
• Lower water table
• Runoff control
• Plant vegetation
• Excavate slide mass

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Landslide Diagnosis "A"
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Landslide Diagnosis "B"
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Landslide Diagnosis "C"
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Landslide Diagnosis "D"