Finals 2 - Ground Subsidence Flashcards
happens when the ground material is displaced into some sort of underground voids, which can only occur in certain rock types.
SUBSIDENCE
Subsidence rock types:
SALT
PEAT
CLAY
LIMESTONE
Types of Subsidence include the following:
Shear Failure
Macrovoids
Slope Failure
Characterized by heaving at the ground surface accompanied by tilting of foundation in it.
Shear Failure
Happens in larger cavities, solution caves in limestone, rare natural cavities in other rocks including salt and basalt, mined cavities in any rocks of economic value.
Macrovoids
A slope collapses abruptly due to weakened self-retainability of the earth under the influence of a rainfall or an earthquake.
Slope Failure
Some fine soils collapse due to restructuring when saturated for the first time, only occurs in a process known as ____________.
Hydrocompaction
______ causes subsidence by 15% of the soil thickness.
Hydrocompaction
is the temporary loss of effective stress of sand during a period of earthquake vibration, where it tends to look like a liquid.
Liquefaction
Liquefaction is triggered by the following:
- When the sand is uniformly graded, with grain size < 0.70 mm
- When it is poorly packed with low relative density
- When it is located below the water table at a shallow depth
Consolidation accelerates under a few meters of placed fill and almost stops when surcharge is removed, usually after one year of pre-construction.
Surcharge
Accelerates water expulsion, so accelerates consolidation.
Drainage
May allow settlement beneath embankment to be compacted during construction time
Drainage
Mixing of cement to improve soil strength
Grouting
Densifying sandy, non-cohesive soils using a crane-supported vibrating poker.
Vibrocompaction
