Soil liquefaction
In soil mechanics, the term "liquefied" was first used by Allen Hazen[1] in reference to the 1918 failure of the Calaveras Dam in California.
He described the mechanism of flow liquefaction of the embankment dam as: If the pressure of the water in the pores is great enough to carry all the load, it will have the effect of holding the particles apart and of producing a condition that is practically equivalent to that of quicksand... the initial movement of some part of the material might result in accumulating pressure, first on one point, and then on another, successively, as the early points of concentration were liquefied.The phenomenon is most often observed in saturated, loose (low density or uncompacted), sandy soils.
This loss of soil structure causes it to lose its strength (the ability to transfer shear stress), and it may be observed to flow like a liquid (hence 'liquefaction').
Resulting soil liquefaction buried the suburb of Balaroa and Petobo village 3 metres (9.8 ft) deep in mud.
The government of Indonesia is considering designating the two neighborhoods of Balaroa and Petobo, that have been totally buried under mud, as mass graves.
In both cases a soil in a saturated loose state, and one which may generate significant pore water pressure on a change in load are the most likely to liquefy.
As pore water pressure rises, a progressive loss of strength of the soil occurs as effective stress is reduced.
A 'flow failure' may initiate if the strength of the soil is reduced below the stresses required to maintain the equilibrium of a slope or footing of a structure.
These tests are performed to determine a soil's resistance to liquefaction by observing the number of cycles of loading at a particular shear stress amplitude required to induce 'fails'.
The term 'cyclic mobility' refers to the mechanism of progressive reduction of effective stress due to cyclic loading.
Such deposits are often found along stream beds, beaches, dunes, and areas where windblown silt (loess) and sand have accumulated.
In this case flow liquefaction occurs, where the soil deforms at a low constant residual shear stress.
When the saturated porous media is subjected to strong ground shaking, pore fluid movement relative to the solid skeleton is induced.
The elastoplastic behavior of soil under earthquake loading has been simulated using a generalized plasticity theory that is composed of a yield surface along with a non-associated flow rule.
[19][20] The other common observation is land instability – cracking and movement of the ground down slope or towards unsupported margins of rivers, streams, or the coast.
Bridges and large buildings constructed on pile foundations may lose support from the adjacent soil and buckle or come to rest at a tilt.
When the water trapped in the batch of sand cannot escape, it creates liquefied soil that can no longer resist force.
In the case of earthquakes, the shaking force can increase the pressure of shallow groundwater, liquefying sand and silt deposits.
The saturated sediment may appear quite solid until a change in pressure, or a shock initiates the liquefaction, causing the sand to form a suspension with each grain surrounded by a thin film of water.
Quick clay is found only in northern countries such as Russia, Canada, Alaska in the U.S., Norway, Sweden and Finland, which were glaciated during the Pleistocene epoch.
Investigators suggested that a 60-mile-per-hour (100 km/h) submarine landslide or turbidity current of water-saturated sediments swept 400 miles (600 km) down the continental slope from the earthquake's epicenter, snapping the cables as it passed.
