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" 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 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 Facts
Landslide 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 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 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) 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 Stability
Type of TriggerNaturalHuman Landslide Triggers (A Few Examples) Removal of Support Addition of Moisture Removal of Vegetation Addition of Weight Oversteepening Vibrations Erosion Excavation Forest firesTimbering Rainfall, Snowmelt Water disposal, Improper grading Volcanic ash, Landslides, Snow Placement of fill (Used like "removal of support") Grading fill steeper than its repose angle Earthquakes, Thunder Blasting, Heavy equipment
Landslide Considerations: Gradient Risk starts at only 15 o Soil / Bedrock Clay soils / shale bedrock are the worst MoisturePore pressure, Lubrication, Weight VegetationRoots anchor soil, remove water SupportMust be maintained WeightDrives 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? #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
Types of Landslides Slump Rotational Slide Rock and soil moving as a unit over a curved failure surface. Complex Landslide Earthflow Mudflow Debris Flow / Avalanche Rock Slide Block 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 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:
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 Stabilization
Landslide Diagnosis "A"
Landslide Diagnosis "B"
Landslide Diagnosis "C"
Landslide Diagnosis "D"