Landslides / Mass Wasting

1. Landslides / Mass Wasting

2. From My Homeowners Policy(Why this is so important)

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

4. Landslide Anatomy Landslide sketch from the West Virginia Geological Survey

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

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

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

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

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

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

11. Landslide Triggers(A Few Examples) 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

12. 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

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

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

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

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

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

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

19. 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.

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

21. 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

22. 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

23. Landslide Diagnosis "A"

24. Landslide Diagnosis "B"

25. Landslide Diagnosis "C"

26. Landslide Diagnosis "D"