human impact

• Terracing:

  • reducing angle of the slope
  • effective for weak unstable slope
  • shear stress reduced, as reduced action of gravity
  • uses lots of space
  • expensive
• Contour Ploughing:

  • perpendicular ploughing to stop rills
  • stops water running down fast
  • creates pores for the water to absorb through
  • harder work for the farmer as the ploughing on an angle
  • shear stress reduced, as reduced water flow
  • could increase rotational slumps
• Afforestation:

  • roots hold the soil together, increases shear strength
  • weight of big trees increase shear stress
  • encourages burrowing animals, decreases shear strength
  • humid acids form after some time, causing chelation
  • roots of trees break up solid material, decreasing shear strength especially base rock
  • water follows root, can decrease surface flow or increase slumping
• Planning controls:

  • limit building
  • limit deforestation
  • limit road building (basal support)
  • minimum safety standards for slope support and water pipes
  • limit run off
  • limit water sinks (drains that release water directly into the subsurface)
• Rock slope stabilisation:

  • rock bolts and dowel bars
  • ground anchors fixed into stable ground, increases basal support
  • drainage holes (especially in weak rock with lots of water flow
  • sprayed concrete over bolted mesh
  • nets over shattered rocks
  • mounds to collect fallen rocks
• techniques to limit rock falls:

  • gabion boxes to support slopes of unconsolidated material e.g. soil, clay, sand
  • grouting to fill gaps between rocks with concrete, as material is too broken for bolts, but not loose enough for nets
  • shotcrete to act as support to keep the slope stable
• road cuttings:

  • layered rocks can have rock slides
  • unconsolidated material can result in mudflow
  • no basal support reduces shear strength
• buildings (cut and fill):

  • steeper slope with more surface run off, reduced shear strength, more pore pressure, and more stress from gravity
  • new land is unconsolidated, weaker, easily saturated, and can cause mudflows
  • buildings are heavy which can increase shear stress
• impacts of vegetation removal - physical:

  • rock is exposed so can be heated or cooled, causing exfoliation, salt crystallisation, and freeze thaw
  • rock can be held together by roots
  • less weathering by roots and burrowing animals