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 306 million years ago

Earth 237 million years ago

Earth 94 million years ago

Earth 14 million years ago

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 being monitored.

”Sink hole”

Karstlandscap

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

Karst landscape

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

mine > collapse

mine > collapse

mine > collapse

Man induced subsidence

• Mining - – Rocks

and minerals

Man induced subsidence

• Mining - – Rocks

and minerals

Risk maps – subsidence due to underground oil shale mine in

Estonia

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