Mass Wasting

1
Mass Wasting

• Mass wasting the downslope movement of material
  under direct influence of gravity
• Slope failure occurs when gravitational forces
  exceed resisting forces within a slope
• Resisting forces include strength, cohesion,
  internal friction, external support collectively
  define the shear strength of the slope
• Angle of repose the steepest angle a slope can
  maintain without collapsing about 30-33o
• Slopes are in a state of dynamic equilibrium,
  constantly adjusting to new conditions, this
  adjustment may include mass wasting

2
Mass Wasting

• Mass wasting controlled by
• -slope angle primary factor in mass wasting,
  the steeper the slope, the less stable it is
  changes are often the result of stream or water
  undercutting
• -weathering reduces consolidated material into
  unconsolidated sediments
• -water content water adds to the weight of
  slope materials and reduces internal friction of
  slope materials
• -vegetation plants can reduce water content via
  root systems, which also anchor unconsolidated
  sediments
• -Overloading often the result of human activity
  such as dumping

3
Types of Mass Wasting

• Mass wasting movements classified based upon
  three major criteria rate of movement, type of
  movement, and type of material involved
• falls rockfalls include extremely rapid movement
  by rocks of any size through the air, occur along
  cliffs, steep canyons, and road cuts, rock
  accumulation is talus
• slides involve movement of material along one or
  more surfaces of failure, may be rock or soil,
  intact or broken, at varying rates two types
  recognized slumps and rock slides
• flows mass movements in which material flows as
  a viscous fluid or displays plastic movement, can
  be mudflows, debris flows, or creep

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Minimizing effects of Mass Wasting

• Hazard assessment slope stability maps
• drainage control
• cut and fill
• benching
• retaining walls
• rock bolts