CHAPTER 7
LANDSLIDES AND MASS WASTING

MASS WASTING:

  •  Any MOVEMENT OR DISPLACEMENT of SOIL OR ROCK down-slope under GRAVITY
  •  Includes: “LANDSLIDES” DEBRIS FLOW, SOIL CREEP and ROCK FALLS
  •  NOT as hazardous as Earthquakes or volcanic Activities
  •  Costs US up to $ 2 billion/year
  •  Occur everywhere in the world on almost every unstable slope: Why?


    • (Figure here)

    Classification of Landslides 3 main criteria

    1.  Type of material, i.e., Rock or Soil
    2.  Mechanism of movement, i.e., sliding, flowing, falling
    3.  Velocity of movement, i.e., fast or slow


      4. Summary of Landslides
      Slides:

      - Slump (slow)
      - Slide/Glide (fast)

      Flows:
      - Avalanche (fast)
      - Creep (slow)

      Falls:
      - Mostly fast
    4. Slumps are the most common landslides
    5. Vary in size form meters to kilometers
    6.  Involves mainly weathered geologic materials


      7. (Figure here)

      Slide/Glide:

    7.  Involves large masses of rocks
    8.  Move along sliding planes
      9. Condition:
    9.  Bedding should be inclined less steeply than inclination of natural slope


      10. (Figure here)

      Causes of Landslides

      Gravity: is driving force for sliding
      Cohesive and frictional forces: are resistive forces: against sliding
      If
      GRAVITY > RESISTIVE FORCES = sliding

    10. Certain Factors increase driving forces & promote sliding


      11. - Increase in slope angle:

      (Figure here)

      Lack of lateral support:

      (Figure here)

      Added weight at the top of the slope

      (Figure here)

    11. Certain Factors reduce strength of slopes and thus reduce resistance to sliding:
    12.  Infiltration to produce ground H2O
    13.  Weathering of minerals and rocks
    14.  Burrowing animals
    15.  Excavation of slopes


      16. Stabilization of Landslides

    16.  Methods based on reducing instability of slopes, i.e., to decrease driving forces OR increase resistive forces

      17. a. Water Drainage and Control:
    17. Water is prevented from infiltrating
      18. putting liners at surface
    18.  - In places with a lot of H2O subsurface, construct horizontal drains to remove water from soils


      19. b. Excavation and Redistribution

    19.  Reconstruct slope: remove materials from top to bottom
    20.  Toe may be removed and replaced with compacted soils i.e., TOE BUTTRESSED


      21. c. Retaining Devices:

    21.  Using stones, concrete, etc. buttress the toes of slopes


      22. Transps (Types) - (5)

    22. Evidences of past/possible landslides:
    23.  Slope> 27° (i.e., 2:1 slope), accurate scars (of former slumps, glides, etc.), bumpy convex upward slopes, springs, wet areas, water-loving plants (i.e., H2O saturation), dip of bedding out of hill, gentle angle of bedding than natural slope.
    24. Evidence of creep:

      25.  
       
       

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