Mass Wasting Flashcards
Mass wasting is due to __________
Slope Failure.
Slopes can become unstable when they are over steepened or comprise of unconsolidated material.
Mass Wasting refers to ______________
Downhill movement of masses of soil, rock, mud or other unconsolidated materials due to gravity
Triggers for Mass Wasting?
- Vibrations from Earthquakes or man-made events
- heavy rainstorms
- volcanic activity
- freeze- thaw action
- Tectonically uplifted areas
- the oversteepening of a slope
The basics of slope stability can be determined by _____________
- the angle of the slope
- material strength
Slope failure (Mass wasting) occurs when ___________
the gravitational force on a slope exceeds its resisting force.
Slope’s shear strength = ______________
The slope material’s strength, cohesion, and the amount of internal friction helps to maintain slope’s stability
What is Angle of repose?
- Maximum angle at which a slope of unconsolidated materials will remain stable
- its shear strength perfectly counterbalances the force of gravity
- function of: particle size, particle shape, moisture content
- Important for stability of unconsolidated materials.
Cohesion of the material is __________
attractive forces that bind the material together
Shear strength or internal friction = _______
The resistance to movement due to cohesion
Unconsolidated: ______________
Consolidated: ______________
Unconsolidated: any loose and un-cemented material such as soil, sediments
Consolidated: Rocks and cemented, vegetated.
Mass movement are classified based on:
- Type of material that move: Consolidated (Rock) or Unconsolidated
- Nature of movement: Fall or Slide or Flow
- Speed of movement: Slow (mm/yr) or Fast (km/hr)
Rock Mass Movements include:
- Rock Falls
- Rock Slides
- Rock Avalanches
Unconsolidated Mass Movements include:
- Creep
- Earthflow
- Mudflow
- Debris flow
- Debris Avalanche
- Slump
- Solifluction
What is Rock Fall?
- Sudden and rapid free fall movement of rock
- Occur on steep slopes
- Freeze thaw action
- Forms Talus piles
Talus: accumulation of rocks at the foot of a steep bedrock cliff
What is Rock Slides?
- Rocks slide rapidly down a slope rather than free falling
Rock Avalanche
- Rock Flows
- One of the most destructive forms of mass movements
- Very fast, large volume
Creep
very slow downhill movement o soil and other debris
Earthflow
- fluid movement of fine grained soils and sediments
- fast
Debris flow
- fluid movement of rock fragments supported by muddy matrix
- contain coarser materials, faster than earth flow
Mudflows
- flowing masses fine-grained material containing large amounts of water
- fast movement due to the high water content
- often initiated after a high rainfall in dry region
Slump
slow slide of unconsolidated material that moves as a unit
Solifluction
- only in cold regions when water in the surface of layers of the soil freeze and thaw
- When surface layers thaw, they become saturated because the water cannot flow down into the frozen layers below
- so upper layers of the soil flow downhill
The occurrence of mass wasting is influenced by _____________
- slope material
- water content
- slope steepness
What is Liquefaction?
- process whereby a water‐saturated material liquefies into a fluid slurry
- one consequence of earth quakes vibration
How does water content affect the stability of unconsolidated materials?
- A thin film of water increases surface tension and increases angle of repose
- However excessive amounts of water will saturate the material and reduce the strength.
What does failure of consolidated materials require?
Overcoming cohesion and shear strength of the material
Engineering Solution?
- Planting vegetation
- Drainage ditches
- Retaining walls
- Rock bolts
The dip angle of bedded rocks has a big effect on slope stability. True or False?
True
Briefly explain why freeze-thaw action can be important in initiating a rock fall?
freeze-thaw action weakens rocks through the expansion and contraction of water within fractures.
The steeper the slope the stronger the shear force. True or False?
True
Earthquake vibrations can cause ______ in water-saturated material.
liquefaction
What causes solifluction?
Seasonal freeze and thaw of surface material
A slope of unconsolidated sand may have the same angle of repose as angular boulders if ________
the sand is damp
