Landslides & Related Phenomena

http://www.youtube.com/watch?v=mknStAMia0Q

Landslides & Related Phenomena

http://www.youtube.com/watch?v=mknStAMia0Q

http://www.youtube.com/watch?v=F31ywRvtNkY

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 sizeparticle shapemoisture 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

http://www.impactlab.com/2008/10/12/the-heyelan-land-slide/

Slope Stability

• Forces on Slopes– Driving forces--tend

to move material down slope

• Weight of material (includes water)*

• Vegetation• Fill material• Building loads

CD

WN

Potential slip plane(clay).

ROCK

A

D = W sin A = driving forcethe downslope component of gravity.

Slope Stability

• Forces on Slopes– Resisting forces--forces that

tend to resist movement• Shear strength

CD

WN

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.