MASS MOVEMENT

Question 1

• Landslide:

Answer 1

a general term, used by media for all types of mass wasting/movement (downslope movement of rock and debris under the influence of gravity/ erosion of the landscape)

Question 2

• Distinguish between causes and triggers for landslides

Answer 2

o Overloading (adding mass)
o Undercutting/ removing support (natural or human related)
o Heavy rainfall
o earthquakes
o volcanic activity

Question 3

• Understand factors that control slope stability

Answer 3

o Slope angle [low =most stable]
 Earthquakes and heavy rainfall (triggers)
o Local relief (topography) [low = most stable]
o Thickness of soil over bedrock [thin= most stable]
o Orientation of geological structures/ planes of weakness in bedrock
 More likely to slide with the planes of weakness
 Lower porosity rocks, holding water- makes planes of weakness
o Climate factors
 Water [some water =most stable, saturated= least stable]
*
 Precipitation [low = most stable, dry/ too much= least stable]
 Ice [no ice= most stable, freeze (taugh cycle) = least stable]
o Vegetation [more= more stable, less vegetation= less stable]

Question 4

• Relationship between gravity and slope stability

Answer 4

o Stable: shear stress < shear resistance
o Instable shear stress > shear resistance
o In unconsolidated materials (soil) SR is considered shear strength
 Shear stress < shear strength = stable
o Angle of repose – unstable at angles larger than repose

Question 5

o Fall:

Answer 5

mass falls through the air
 Rock fall- small individual rock pieces form a talus slope

Question 6

o Slide

Answer 6

failure plane along a definite slip surface-mass stays intact
 Transitional (glide block)
 Rotational (slump)
* Concave surface, thick soils and soft sedimentary

Question 7

flow

Answer 7

material moves as a viscous fluid (varying amounts of water)
 Debris flows-
* earthflow
* mudflow- high amount of water, incredibly fast over great distance
 Debris avalanche- fast fluidized rubble or debris
* High velocity
* Water and/or ice fluidize the debris giving it high speed

Question 8

 Slope failure is classified

Answer 8

• Creep- imperceptibly slow type of flow
  o Soil creeps- not notable over short time period (soil ripples), shear stress causes deformation, not failure

Question 9

o How do we decrease slop hazards

Answer 9

o How do we decrease slop hazards
 Identify unstable and potentially unstable slopes by geologic mapping
 Legislate appropriate zoning laws- enforce them
 Control/ stop existing sliding
 Engineer structure to prevent new landslides
o Build retaining walls
o Surface/subsurface drainage
o Revegetate slopes
 ‘hydroseeding, applying jute netting (protecting wind/water erosion)
o Cover and regrading slopes
o Chicken wire – rock falls
o Use od shotcrete
o Rock bolts
o Contain/ redirecting hazards