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"