Landslides & Related Phenomena

Landslides & Related Phenomena

Introduction to Landslides Landslide – rapid downslope movement of “coherent” mass Slope failure/mass wasting- general term (e.g. mudflows, rockfalls, snow/debris avalanches) Subsidence (downward movement)

Introduction to Landslides

Slope Processes and Slope Stability “If it’s not a river or a beach, it’s a hillslope, of one ilk or another” –Most common landforms –Appear static; actually are dynamic Valley –Moving downhill Creep Avalanche/rock fall –Moderate events are the most important Magnitude Frequency

Slope Processes and Slope Stability Processes –Slope elements Convex slope/crest Free-face –Angle of repose Debris slope Convex slope/wash slope

Angle of repose: particle size particle shape moisture content Angle of Repose

Slope Processes and Slope Stability Processes –Slope movements or deformation Flowage/flow Sliding Falling Subsidence Classification –Type of movement –Slope material –Amount of water present –Rate of movement

Classification of Mass Movement Creep

Types of Movement

Slope Movements

Slope Stability When does a slope fail? What is the critical threshold that’s exceeded? Variables: –Material type –Slope –Topography –Climate –Vegetation –Water** –Time.

Landslides & Related Phenomena

Slope Stability Forces on Slopes –Driving forces--tend to move material down slope Weight of material (includes water)* Vegetation Fill material Building loads C D W N Potential slip plane (clay). ROCK A D = W sin A = driving force the downslope component of gravity.

Slope Stability Forces on Slopes –Resisting forces--forces that tend to resist movement Shear strength C D W N Potential slip plane (clay). ROCK A N = W cos A = the normal component of W contributes to the shear strength along the slip plane contributes to the resisting force.