MASS WASTING (ch. 11)
downslope movement of material due to gravity
Effects: erosion, loss of life, property damage
CAUSE: GRAVITY
Gravitational force increases with:
slope angle
weight
When grav force > shear strength:
FAILURE
Shear strength:
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Internal: friction between grains, cohesion and strength
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External: vegetation, retaining walls
CAUSES OF FAILURE
Increase in gravitational force
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oversteepening
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overloading
Decrease in shear strength
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increased water pressure
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weathering
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removal of vegetation
Triggers:
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heavy rainfalls
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Earthquakes
Quick clays: liquefy when disturbed (liquefaction)
TYPES OF MASS MOVEMENT
Creep: Very slow, most common
Fall: rocks fall through the air
Slide or Slump: movement of material along a failure surface
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slide: planar surface
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slump: curved surface
Flow: materials moves as a viscous fluid (water added)
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Mudflow: most fluid, fastest
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Debris flow: larger-sized particles than a mudflow
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Earthflow: slower
MINIMIZING DAMAGE
identify landslide-prone areas, examine geology
“Soft” solutions:
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zoning
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revegetation
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monitoring
“Hard” solutions: engineering
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increase drainage
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slope grading
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construct retaining walls, debris dams