What is liquefaction?
Liquefaction can be explained as the phenomena when soil behaves as a liquid when there is seismic activity occurring in that area.
How does liquid behave?
Liquid flows down and causes the soil particles to separate and lose contact.
What areas are at risk?
An area is at risk for liquefaction if the soil underground is saturated or if man-made landfill is utilized. Loose, young soils are also susceptible to this phenomena.
According to the Earthquake Engineering Research Institute, the effects of liquefaction can take a number of different forms. Among them are: flow failures, lateral spreads, ground oscillation, and loss of bearing strength- among others.(www.eeri.org).
This refers to the displacement of masses of soil. This may include soil that is fully liquefied as well as portions of material that are not liquified, in addition to the liquefied soil. Flow failures are common when “relatively steep slopes” are present. The instability caused by liquefaction pushes the liquefied soil down the slope.
Lateral refers to the side or sides and displacement refers to the moving of something from its position. A lateral spread refers to the displacement of blocks of soil, resulting from the forces created by an earthquake. As compared to flow failures, lateral spreads most often occur on gentle slopes. This can affect building foundations as well as pipelines.
Examples of Lateral Spreads In Past Earthquakes
During the 1906 San Francisco earthquake, lateral spreading had a devastating effect on the pipelines in the affected areas. Due to the damaged pipelines, the fires burned for much longer than they would have had there been access to water.
In the 1964 Alaska Earthquake, bridges were severely damaged and in some cases destroyed due to the effects of lateral spreading.
The Earthquake Engineering Research Institute explains that if the ground is too flat or the slope is too gentle for lateral displacement to occur, the resulting effect is ground oscillation. During the 1989 Loma Prieta Earthquake, the effects of ground oscillation were apparent in the sidewalks that were buckled as a result of the soil oscillation.
Photo Courtesy of USGS
A modern day example of liquefaction is the infamous Millennium Tower in San Francisco, which as many people know is sinking and tilting. This issue can be explained by the soil that millennium stands on, largely man-made fill- which is prone to liquefaction.
Liquefaction prone areas can be identified, but when exactly it will happen cannot be predicted. Researchers have made strides in identifying areas with the potential for liquefaction which has helped provide insight into hazard areas.