Granular materials like sand appear like a solid but under certain circumstances they can behave like a liquid. How this exactly happens is still a physical mystery.
Granular flow in vacuum
Water can play a role, like in a debris-flow, but there also exist examples of dry sand-flows, flowing almost like a liquid despite no water being present. Some experts think that such grain-flows flow on a cushion of air, but deposits similar to terrestrial grain-flows have also been observed on celestial bodies without an atmosphere, suggesting that even in a vacuum, granular flow is possible.
Dynamic liquefaction by shakes
One theory explains liquefaction of granular materials as a sort of dynamic liquefaction, caused by vibrations or shaking. In a granular material, forces are distributed along “bridges,” the contacts of the single grains between each other, into the entire framework.
Shaking such grainy material can cause the tiny pores, found between the grains, to collapse. As the entire framework collapses, the material loses its stability and behaves like a liquid, where all the grains can move without any friction and independently, until a new framework is formed.
This theory could explain why granular materials can suddenly behave like a liquid but also apparently freeze within their flow ( debris- or granular-flows often move in “waves”, accelerating and decelerating quickly).
Liquefaction and Earthquake
Soil liquefaction can play an important role during an earthquake, as the shaking will break down the framework of the soil (a mixture of grainy rock fragments, water and air).
The liquefied soil no longer supports the weight of a building but will be squeezed out around the building’s foundations, causing the partial or complete collapse of the buildings. Similar effects can sink ships too.
Cargo ship sunk
On May 18, 2005, the Hong-Kong registered ship Hui Long, a midsize cargo ship, was sailing from the harbor of Sungei-Pakning in Indonesia to India. The ship was loaded with 11,245 tons of mixed general cargo, including 5,185 tons of crushed mineral ore. Passing near Sri Lanka the ship suddenly tilted sidewards in a moderately agitated sea. Despite the efforts of the crew to stabilize the ship, it eventually sank the next day.
What happened?
Liquefaction of the transported crushed mineral ore cargo, could explain the incident. When the granular cargo liquefies, in response to vibrations caused by the motion of the waves, it can shift or slosh inside a ship’s cargo bay. The now unevenly distributed weight destabilizes the ship.
As soon as the ship slightly tilts, the effect can reinforce itself. Now more and more material flows to one side of the ship. In the end, unless the sloshing is stopped, water will enter the tilted ship through the hatch covers.
Liquefaction and Sinking cargo ships
Many cargo ships transport granular materials, like fertilizers, sand, ore or grain. On average, ten ships transporting such a type of cargo are lost at sea every year. In many cases the cause of the sinking of the ship remains unknown, but sudden liquefaction of the cargo could play a role in many such cases.
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Source: Forbes
