What Causes Liquefaction Ground Failure?

Liquefaction ground failure occurs as the result of an earthquake in areas where the ground is composed more of sand and silt, with a heavy moisture content, and less of solid rock or clay. Loose silt and sand that is water saturated will behave like a liquid during an earthquake. The ground effected literally turns into a mud.

What are the causes of liquefaction ground failure?

There are three different factors that need to combine for liquefaction ground failure to occur. The first is that the land must be primarily made up of loose and granular sediment or sand. The second element needed is a high content of moisture or ground water. Either heavy rain or a high water table can provide this. The third element is a severe shaking of the ground due to an earthquake. When all three of these factors combine ground liquefaction failure can occur.

The sediment layer and water content do not need to be close to the surface. Liquefaction failure can occur well below the ground in layers. When the underground layer fails the above layers can also fail. Liquefaction ground failure is simply the transition of ground that was in a solid state to ground that has become a liquid.

Where can liquefaction failure occur?

The San Francisco Bay area is one where liquefaction ground failure is likely. Marsh areas that have been filled with dredged materials to create a man made land area are very vulnerable to liquefaction during an earthquake.

Niigata, Japan was effected by liquefaction ground failure during an earthquake in 1964. Similar failure occurred in Costa Rica in April of 1991. Any areas that are built on loose sediment with a high water content are susceptible to liquefaction failure.

Damage that can occur from liquefaction ground failure:

When the ground liquefies it loses it's ability to support any structures built on it. Buildings can collapse and sink. Even trees and other agriculture can be effected by liquefaction. Ground slides can occur from lateral spreading of the area effected. Liquefied layers that are underground can cause the failure of gas lines and any other buried utilities.

Sand volcanoes can be formed. Water, laden with sand, from a underground failure will actually erupt to the surface. Empty fuel tanks and other light weight structures can float to the surface in an area effected by liquefaction ground failure. Pavement and sidewalks can buckle from the ground oscillation.

References:

http://pubs.usgs.gov/of/1996/ofr-96-0263/groundf2.htm

http://geomaps.wr.usgs.gov/sfgeo/liquefaction/aboutliq.html

http://www.eeri.org/cds_publications/earthquake_basics_series/LIQ1.pdf