Subsidence Flashcards
subsidence
the sinking of the Earth seuface
Causes of Subsidence
AGeological 1. Earthquakes 2.Volcanic Activity 3.Rx solution Bhuman 1.Hydrocompaction 2.mining 3.subsurface fluid removal
A1Earthquakes -natural subsidence
vertical displacement along fault planes
A2volcanic activity -natural subsidence
collapse into empty magma chamber -> coldera
A3.rx solution -natural subsidence
the dissolution of rx near surface by percolating grdh2o
rx that dissolve in solution
acidic grdh2o percolate thru the fracture & enlarging the fractures into larger cavities
A3. karst terrain/ topography
sfsdf
A3.sinkholes
depression of the grd that form in karst terrain by dissolution of carbonate rx
A3.measures of sinkholes
seismic - used to locate undrgrd caves + not build above the cave
monitor water table - maintain recharge»_space; discharge conditions
B1.hydrocompaction
results from the heavy of application of water to the land surface on certain loose dry soils
B1.collapsible soils
have 1/2 the density of rx therefore lots of pores
added water, the open structure will collapse
B1.measures of hydrocompaction
study to find the location of the collapsible soil & dont build on them
presoak the soil then backfill holes
B2.mining
removal of the ore forms tunnels in the subsurface resulting in collapse the overlying soil and rx
B2.measures of mining
leave natural rx pillars to support the tunnels
install man-made support
backfill with waste rx
B3. Subsidence Fluid Removal
the fluid in the rx pores removed, hydrostatic pressure decreased, less P support for the overburden
the grains rearrange their packing structures to more compact one resulting in subsidence of rx
measures of Fluid Removal
1. oil gas production backfill brine into the reservoir rx to maintain subsurface P Increase production rate of O+G decrease possibility of subsidence increase profits of the company 2 grdh2o monitor recharge, discharge water restriction import h2o
