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Subsidence . Natural Man induced. Natural subsidence. Plate tectonics – regional changes in land and water . Earth 514 million years ago . Earth 458 million years ago. Earth 390 million years ago. Earth 3 06 million years ago. Earth 237 million years ago.

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subsidence

Subsidence

Natural

Man induced

natural subsidence
Natural subsidence
  • Plate tectonics – regional changes in land and water
natural subsidence10
Natural subsidence
  • Plate tectonics – regional changes in land and water
  • Karst – chemical weathering of soluble rocks
karst
Karst

Collapse of solution cavities in soluble rocks

sink hole
Sink hole

Collapse of solution cavities in soluble rocks

sink hole13
Sink hole

A large subsidence occurred in Waihi early in the morning (about midnight) on the 13 December. The large 50m diameter sinkhole that developed destroyed a house, a caravan, several cars and smaller buildings.  Another house was undermined and a third is perched on the edge.  The road has collapsed and radial cracking has apeared around the feature.  Movement is beingmonitored.

karst lands c ap e
Karstlandscape

water and carbon dioxide mix to form carbonic acid which disolves the limestone

karst lands c ap e16
Karstlandscape

water and carbon dioxide mix to form carbonic acid which disolves the limestone

formation of karsts
formation of karsts
  • with time the fractures and joint widen
formation of karsts18
formation of karsts

underground rivers and large caves form

formation of karsts19
formation of karsts
  • When the weight of the overlying ground exceeds the strength of the rock then collapse occurs
man induced subsidence
Man induced subsidence
  • Mining -
    • Water
    • Oil
    • Gas
    • Rocks and minerals
  • Loading
man induced subsidence22
Man induced subsidence
  • Mining -
    • Compaction
    • Collapse
    • Faults
man induced subsidence23
Man induced subsidence
  • Mining
    • Compaction
    • Collapse
    • Faults
extraction of liquids or gas
Extraction of liquids or gas
  • compaction
  • collapse
  • faults
man induced subsidence25
Man induced subsidence
  • Mining -
    • Compaction
    • Collapse
    • Faults
man induced subsidence26
Man induced subsidence
  • Mining -
    • Compaction
    • Collapse
    • Faults
man induced subsidence27
Man induced subsidence
  • Mining -
    • Compaction
    • Collapse
    • Faults
man induced subsidence28
Man induced subsidence
  • Mining -
    • Oil
    • Gas
man induced subsidence29
Man induced subsidence
  • Mining -
    • Oil
    • Gas
man induced subsidence30
Man induced subsidence
  • Mining -
    • Oil
    • Gas
  • Mitigation – pump in water to hold up the overburden
man induced subsidence31
Man induced subsidence
  • Mining -
    • Rocks and minerals
man induced subsidence35
Man induced subsidence
  • Mining -
    • Rocks and minerals
man induced subsidence36
Man induced subsidence
  • Mining -
    • Rocks and minerals
loading
Loading
  • Compaction
  • Volume change
  • Subsidence
liquifaction
Liquifaction –
  • When shaken the strength of the soil is lost
shaking
Shaking
  • earthquake
  • vibrations from
    • roads
    • railroads
shaking41
Shaking
  • liquefaction
expansive soils
Expansive soils
  • expansive clays
    • Bentonite
    • Montmorilonite
expansive soils43
Expansive soils
  • Expansive clays
    • Bentonite
    • Montmorilonite
management
Management
  • Accept – do nothing
  • Avoid – plan away
  • Defend – build to protect against
identification of the potential problem
Identification of the potential problem
  • Risk maps to avoid
    • Aid in planning
  • Defense
    • Natural – difficult to defend against
      • Plate tectonics
      • Karst – important to understand the processes involved
    • Man induced –
      • Mining – supports, adding fluids, backfilling