Landslides and the safety factor (hillslope transport) Flashcards
Lecture 8 Wednesday 9/11
what are some characteristics of landslides?
- internally crumbling and deforming
- whole coherent mass moves
- there is a slide plane
what is the slide plane?
- a discreet plane below which there is no more movement
- point of failure
what is the difference between a creep and landslide?
mass moves above a plane at a constant rate whereas in creep the whole soil profile slowly moves downslope (velocity gradient too)
what are the conditions necessary for a material to move?
function of:
- slipperiness of the slide plane (wetness, pore pressure counteracts the weight of material, floats)
- stickiness
- weight
- the steepness of plane
What would the texture of the deposit be as it moved down?
What is the safety factor?
the forces resisting a landslide vs the forces driving it to become a landslide
What is the safety factor formula?
resisting force/driving force = C + σntanФ/τ = (C+ρghcos2α-μtanФ)/ ρghsinαcosα
What does a safety factor of less than one mean?
if the driving force is bigger than resisting = landslide
What does a safety factor of more than one?
if the resisting force is bigger than the driving force = stable
What does a safety factor of one mean?
instability, teetering edge
what are the different forces acting on a moving object?
friction, normal stress, and shear stress
What is W? what is its formula?
weight of the block
densitygravitational accelerationthickness*the angle that it’s at (cosα) on a slope
what is σn? what is its formula?
normal stress: force that holds down object on plane
Wcosα
what is τ? What is its formula?
Shear stress: force pulling an object down a slope
Wsinα
What is C?
cohesion, y- intercept
