Transcript Document
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 Collapse of solution cavities in soluble rocks Karst 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 ”Sink hole” Karst landscape water 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 • earthquake • vibrations from – roads – railroads Shaking 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