Landslides / Mass Wasting

From My Homeowners Policy
(Why this is so important)

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

Landslide Anatomy
Landslide sketch from the West Virginia Geological Survey

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

Landslide Geography
• Steep Slopes
• Slide-Prone Soils
• High Precipitation
• National Landslide Overview Map ( connect )

Slide-Prone Area Map
Slide-prone area map by Peter Lessing, West Virginia Geological Survey

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

Angle of Repose Determined By
• Particle size
(higher for large particles)
• Particle shape
(higher for angular shapes)
• Shear strength
(higher for high shear strength)

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

Landslide Triggers
(A Few Examples)
Type of Trigger
Removal of
Support
Addition of
Moisture
Removal of
Vegetation
Addition of
Weight
Oversteepening
Vibrations
Natural Human
Erosion
Rainfall,
Snowmelt
Forest fires
Volcanic ash,
Landslides, Snow
(Used like "removal of support")
Earthquakes,
Thunder
Excavation
Water disposal,
Improper grading
Timbering
Placement of fill
Grading fill steeper than its repose angle
Blasting, Heavy equipment

Landslide Considerations:
Gradient Risk starts at only 15 o
Soil / Bedrock Clay soils / shale bedrock are the worst
Moisture Pore pressure, Lubrication, Weight
Vegetation
Support
Roots anchor soil, remove water
Must be maintained
Weight Drives the slide, compression of substrate
Vibrations Result in a loss of friction
Oversteepening Exceeding the angle of repose

#1
What was the trigger?
Who is to blame?

#2
What was the trigger?
Who is to blame?

#3
What was the trigger?
Who is to blame?

#4
What was the trigger?
Who is to blame?

#5
What was the trigger?
Who is to blame?

#6
What was the trigger?
Who is to blame?

Types of Landslides
Slump
Rotational Slide
Earthflow
Mudflow
Debris Flow / Avalanche
Rock and soil moving as a unit over a curved failure surface .
Similar to a slump, but the material breaks-up and flows.
Much higher moisture content than an earthflow
- the material makes a "batter" with water.
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.

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

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

Landslide Stabilization
• Get expert advice
• Your efforts will probably give temporary relief
• Support the base
• Anchor through slip plane
• Lower water table
• Runoff control
• Plant vegetation
• Excavate slide mass

Landslide Diagnosis "A"

Landslide Diagnosis "B"

Landslide Diagnosis "C"

Landslide Diagnosis "D"