EOSC 114 Module 4 Practice Questions with Complete Solutions Rated A+
Mass Movement/ Mass Wasting - Answers refers to downslope motion of soil/rock materials under
influence of gravity
Landslide - Answers General term for mass movements - occur when gravity pulling material down slope
exceeds slopes material's internal resistance to shear or failure - materials move by sliding or shearing
along weak failure plane or number of planes
2 Components of gravity - Answers Gp - part that acts perpendicular to the slope - helps hold an object
to it's place on the slope
Gt - acts tangentially to slope surface - parallel and down the slope, causes shear stress (more the
steeper the slope is)
Shear Strength - Answers -defined as internal resistance of body to shear stress or a material's internal
shearing resistance
-results cause gravity pulls slope material downslope, force resisting this movement will be induced,
including frictional resistance and cohesion among particles of slop material
Shear Strength Factors - Answers Type of soil/rock
Condition of geologic materials (how eroded)
Presence of weak surfaces (joints/faults)
Pore water pressure within the slope
Safety Fs - Answers Ratio of shear strength at failure Sf to average shear stress T (Sf/T)
-slope failure occurs when gravity parallel to slope (shear stress) becomes greater than the materials
making up the slope which is acting to hold itself in place (shear strength)
-can be thought of as ratio of forces that resist movements to forces that drive movement
if greater than 1, slope is stable, if less, slope failure expected
effective stress - Answers net sum of opposing effects of normal stress and pores water pressure
(normal stress - pore water pressure)
can be viewed as a sum of contact forces between grains, divided by total area
can try to manipulate this to make stopes more stable
, cause - Answers factor that makes slopes susceptible to movement
trigger - Answers event that actually initiates movement by driving FS<1.0
e.g. earthquakes, volcanoes, tons of rain, mining, irrigation, etc
trigger frequency - Answers how often an event occurs that sets off a landslide.
can be natural, human induced, or combo of the two
Erosion - Answers transport of material away from it's source - removing material at base of slope can
cause slope failure in 2 ways:
1) driving mass > resisting mass
2) slope steepness at base increases so shear stress > shear strength
Rapid Erosion - Answers Large storms (heavy rainfall or pounding waves) can work to rapidly erode
undercut coastal slope - large landslides (e.g. UBC 1935)
Vegetation effects - Answers affects shear strength - roots increase soil cohesion and strength by helping
bind loose material
decrease surface erosion by absorbing extra water
Water Content effects - Answers -excessive water increases mass and shear stress
-fluid pressure - reduces friction, slope failure
- water increases weathering of rocks when it flows in narrow rock fractures - freeze thaw cycles can
wedge em appart, fall !!
- water can help or hinder cohesion - helps bind shit, but when too much, can't bind
Precipitation Effects - Answers more frequent landslides after heavy rainfalls (erosion and pore
pressures)
big storms are common triggers
heavy/prolonged rain can increase goundwater levels too - trigger more deep seated/slower moving
landslides (like slumps)
Volcanic Activity Effects - Answers loose ash on hillsides followed by accelerated erosion can be
triggered by intense rainfalls
- historic large langslides
e.g. mt st helens
Mass Movement/ Mass Wasting - Answers refers to downslope motion of soil/rock materials under
influence of gravity
Landslide - Answers General term for mass movements - occur when gravity pulling material down slope
exceeds slopes material's internal resistance to shear or failure - materials move by sliding or shearing
along weak failure plane or number of planes
2 Components of gravity - Answers Gp - part that acts perpendicular to the slope - helps hold an object
to it's place on the slope
Gt - acts tangentially to slope surface - parallel and down the slope, causes shear stress (more the
steeper the slope is)
Shear Strength - Answers -defined as internal resistance of body to shear stress or a material's internal
shearing resistance
-results cause gravity pulls slope material downslope, force resisting this movement will be induced,
including frictional resistance and cohesion among particles of slop material
Shear Strength Factors - Answers Type of soil/rock
Condition of geologic materials (how eroded)
Presence of weak surfaces (joints/faults)
Pore water pressure within the slope
Safety Fs - Answers Ratio of shear strength at failure Sf to average shear stress T (Sf/T)
-slope failure occurs when gravity parallel to slope (shear stress) becomes greater than the materials
making up the slope which is acting to hold itself in place (shear strength)
-can be thought of as ratio of forces that resist movements to forces that drive movement
if greater than 1, slope is stable, if less, slope failure expected
effective stress - Answers net sum of opposing effects of normal stress and pores water pressure
(normal stress - pore water pressure)
can be viewed as a sum of contact forces between grains, divided by total area
can try to manipulate this to make stopes more stable
, cause - Answers factor that makes slopes susceptible to movement
trigger - Answers event that actually initiates movement by driving FS<1.0
e.g. earthquakes, volcanoes, tons of rain, mining, irrigation, etc
trigger frequency - Answers how often an event occurs that sets off a landslide.
can be natural, human induced, or combo of the two
Erosion - Answers transport of material away from it's source - removing material at base of slope can
cause slope failure in 2 ways:
1) driving mass > resisting mass
2) slope steepness at base increases so shear stress > shear strength
Rapid Erosion - Answers Large storms (heavy rainfall or pounding waves) can work to rapidly erode
undercut coastal slope - large landslides (e.g. UBC 1935)
Vegetation effects - Answers affects shear strength - roots increase soil cohesion and strength by helping
bind loose material
decrease surface erosion by absorbing extra water
Water Content effects - Answers -excessive water increases mass and shear stress
-fluid pressure - reduces friction, slope failure
- water increases weathering of rocks when it flows in narrow rock fractures - freeze thaw cycles can
wedge em appart, fall !!
- water can help or hinder cohesion - helps bind shit, but when too much, can't bind
Precipitation Effects - Answers more frequent landslides after heavy rainfalls (erosion and pore
pressures)
big storms are common triggers
heavy/prolonged rain can increase goundwater levels too - trigger more deep seated/slower moving
landslides (like slumps)
Volcanic Activity Effects - Answers loose ash on hillsides followed by accelerated erosion can be
triggered by intense rainfalls
- historic large langslides
e.g. mt st helens
