Landslides / Mass WastingLandslides / Mass Wasting
From My Homeowners Policy(Why this is so important)
From My Homeowners Policy(Why this is so important)
Mass WastingMass Wasting
• Any downslope movement of rock and soil under the influence of gravity.
• "Landslide"
• "Rockslide" "Creep" "Rock Fall"
• Any downslope movement of rock and soil under the influence of gravity.
• "Landslide"
• "Rockslide" "Creep" "Rock Fall"
Landslide sketch from the West Virginia Geological Survey
Landslide AnatomyLandslide Anatomy
• Most are very slow (inches per year)• Most occur naturally• Homeowners insurance does not pay.
• Most are very slow (inches per year)• Most occur naturally• Homeowners insurance does not pay.
Important Landslide FactsImportant Landslide Facts
Landslide GeographyLandslide Geography
• Steep Slopes• Slide-Prone Soils• High Precipitation• National Landslide Overview Map
• Steep Slopes• Slide-Prone Soils• High Precipitation• National Landslide Overview Map (connect)
Slide-Prone Area MapSlide-Prone Area Map
Slide-prone area map by Peter Lessing, West Virginia Geological Survey
Angle of ReposeAngle of Repose
• The maximum slope at which loose, cohesionless material is stable
• The maximum slope at which loose, cohesionless material is stable
Angle of Repose Determined ByAngle of Repose Determined By
• Particle size
(higher for large particles)
• Particle shape
(higher for angular shapes)
• Shear strength
(higher for high shear strength)
• Particle size
(higher for large particles)
• Particle shape
(higher for angular shapes)
• Shear strength
(higher for high shear strength)
• Increase the slope
• Decrease the shear strength
• Increase the effect of gravity
• Increase the slope
• Decrease the shear strength
• Increase the effect of gravity
Upsetting StabilityUpsetting Stability
Type of Trigger Natural Human
Landslide Triggers(A Few Examples)
Landslide Triggers(A Few Examples)
Removal ofSupport
Addition of Moisture
Removal ofVegetation
Addition ofWeight
Oversteepening
Vibrations
Erosion Excavation
Forest fires Timbering
Rainfall,Snowmelt
Water disposal,Improper grading
Volcanic ash,Landslides, Snow
Placementof fill
(Used like "removalof support")
Grading fill steeperthan its repose angle
Earthquakes,Thunder
Blasting, Heavyequipment
Landslide Considerations:Landslide Considerations:
Gradient Risk starts at only 15o
Soil / Bedrock Clay soils / shale bedrock are the worst
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
Oversteepening Exceeding the angle of repose
What was the trigger?
Who is to blame?
What was the trigger?
Who is to blame?
#1
What was the trigger?
Who is to blame?
What was the trigger?
Who is to blame?
#2
What was the trigger?
Who is to blame?
What was the trigger?
Who is to blame?
#3
What was the trigger?
Who is to blame?
What was the trigger?
Who is to blame?
#4
What was the trigger?
Who is to blame?
What was the trigger?
Who is to blame?
#5
What was the trigger?
Who is to blame?
What was the trigger?
Who is to blame?
#6
Types of LandslidesTypes of Landslides
SlumpRotational Slide
Rock and soil moving as a unit over a curved failure surface.
ComplexLandslide
Earthflow
MudflowDebris Flow / Avalanche
Rock SlideBlock Glide
Creep
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.
A block of bedrock sliding down dip.
Gradual downslope movement of rock and soil.
A combination of two different slide types.
• Curved trees• Stuck windows• Stuck doors• Leaning walls• Plaster cracks• Foundation cracks• Damaged chimneys• Leaning poles• Scarps• Toes• Seeps• Pavement damage
• Curved trees• Stuck windows• Stuck doors• Leaning walls• Plaster cracks• Foundation cracks• Damaged chimneys• Leaning poles• Scarps• Toes• Seeps• Pavement damage
Recognizing Problem AreasRecognizing Problem Areas
• 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
• 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
Before buying on a hillside:Before buying on a hillside:
• 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
• 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 StabilizationLandslide Stabilization
Landslide Diagnosis "A"Landslide Diagnosis "A"
Landslide Diagnosis "B"Landslide Diagnosis "B"
Landslide Diagnosis "C"Landslide Diagnosis "C"
Landslide Diagnosis "D"Landslide Diagnosis "D"