Quicksand

Quicksand (even quicksand ) is a suspension of sand in water. Although he seems fairly firmly in the undisturbed state, it behaves under the influence of pressure as a special type of liquid, a non-Newtonian fluid.

Operation

When vibration or pressure auflagerndem the sand grains lose contact with each other and shift. Their aqueous environment without major resistance Dry sand would condense and solidify in these circumstances.

The only very small pores between the sand grains prevent the rapid drainage of fluid. ( Gravel is much more permeable and not exhibit this phenomenon consequently ): The entire suspension will be a temporary to a " liquified " thixotropic state that lasts until get the sand grains after pressing out of the pore water re-establish contact with each other.

The effect can only occur if

• The sand grains were freshly showered or rearranged uncemented grains are thus still in loose relation to each other and the pore spaces fill slightly with water.
• There is enough water to completely fill the pore spaces: On rivers in sedimentation zones with sandy sediment (meaning probably in the river underflow), at the source under constant water supply as well as in the coastal areas of lakes and seas.

A water wonder and ground can prevent almost completely with appropriate terrain rapid drainage of water pressed and re-solidification of the sand body.

Occurrence of quicksand

Beautiful to look at the quicksand in sand pictures: In fresh trickling sand larger amounts of water are still included, the sand thickens when "Call waiting" immediately. The grains of sand rub against each other, the suspension is thickened by shear, and the internal resistance - the viscosity - of the suspension rises. Tilting movements, however, let the liquid state back to life.

Hazards

Quicksand is especially by exaggerated representations in adventure literature and films in the reputation of being dangerous to life when you put device into it. This is only partially correct. The high overall density of the water dispersion of sand makes the sinking deeper than up to about the stomach almost impossible, since the density of the human body is close to that of water; Quicksand, however, has at least twice. A complete submersion is excluded. In tidal flats, however, can be a death trap sinking into quicksand in emerging flood actually.

To be rid without help from quicksand, can be difficult or even impossible, depending on the nature of the subsurface and depth of sinking. Are the legs already sunk too deep, it is recommended to move as little as possible, since the sand comes to rest after some time and the body is slightly distended. In affected areas, the emergency services are equipped with pumps that liquefy the mixture as far as water injection means that a recovery is possible.

Quicksand effects ( liquefaction ) can cause collateral damage when larger areas thixotropic sands are also affected during earthquakes - such as the earthquake in Kobe in 1995 or in the demise of Port Royal 1692nd

" Dry " quicksand

In the journal Nature published Detlef Lohse ( University of Twente in Enschede) and co-authors in 2004 an experiment that could explain the "dry" quicksand.

By means of an air stream was bubbled through a perforated container with fine sand ( silt ), was a very loose packing of the sand layer can be achieved. Then sank one of falling, metal-filled ball in the material and sometimes produced a veritable on spraying fountain. Given their results, the researchers speculated that air turbulence in the desert could sell sand in a similar loose pack that even humans, camels or vehicles could sink into it - like shown in adventure films. However, in the simple transfer of laboratory experiments on the scale desert caution: in the few cm thick layer of sand in the laboratory is the weight of the sand, pressing on the microstructure of the grains of sand, minimal. In contrast, when it comes to sand layers in a thickness of 3, 4 or more meters, which are a prerequisite for the complete submersion of a person or of a camel: A cubic meter of dry sand already weighs about 1.5 tons. With each new layer of sand, which is deposited on a layer exists, increases the pressure on the grains of sand, the sand begins to set ( compaction ). An extremely loose sand structure, as prepared in the laboratory on a small scale changes in a multi-ton vertical load very quickly its physical properties.