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Subsidence - PowerPoint PPT Presentation
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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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Presentation Transcript
Natural subsidence
- Plate tectonics – regional changes in land and water
Natural subsidence
- Plate tectonics – regional changes in land and water
- Karst – chemical weathering of soluble rocks
Karst
Collapse of solution cavities in soluble rocks
Sink hole
Collapse of solution cavities in soluble rocks
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.
Karstlandscape
water and carbon dioxide mix to form carbonic acid which disolves the limestone
Karstlandscape
water and carbon dioxide mix to form carbonic acid which disolves the limestone
formation of karsts
- with time the fractures and joint widen
formation of karsts
underground rivers and large caves form
formation of karsts
- When the weight of the overlying ground exceeds the strength of the rock then collapse occurs
Formed by the catastrophic collapse of an underlying cave, the Lost River Cave Valley
Man induced subsidence
- Mining -
- Water
- Oil
- Gas
- Rocks and minerals
- Loading
Man induced subsidence
- Mining -
- Compaction
- Collapse
- Faults
Man induced subsidence
- Mining
- Compaction
- Collapse
- Faults
Extraction of liquids or gas
- compaction
- collapse
- faults
Man induced subsidence
- Mining -
- Compaction
- Collapse
- Faults
Man induced subsidence
- Mining -
- Compaction
- Collapse
- Faults
Man induced subsidence
- Mining -
- Compaction
- Collapse
- Faults
Man induced subsidence
- Mining -
- Oil
- Gas
Man induced subsidence
- Mining -
- Oil
- Gas
Man induced subsidence
- Mining -
- Oil
- Gas
- Mitigation – pump in water to hold up the overburden
Man induced subsidence
- Mining -
- Rocks and minerals
Man induced subsidence
- Mining -
- Rocks and minerals
Man induced subsidence
- Mining -
- Rocks and minerals
Loading
- Compaction
- Volume change
- Subsidence
Liquifaction –
- When shaken the strength of the soil is lost
Shaking
- earthquake
- vibrations from
- roads
- railroads
Shaking
- liquefaction
Expansive soils
- expansive clays
- Bentonite
- Montmorilonite
Expansive soils
- Expansive clays
- Bentonite
- Montmorilonite
Management
- Accept – do nothing
- Avoid – plan away
- Defend – build to protect against
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
