Zusammenfassung
The image of quicksand merciless swallowing a victim has inspired the
fantasy of kids and helped writers and moviemakers to get rid of evil
figures. Is this really possible? This is still disputed since till
today it is not even clear what quicksand exactly is. In soil mechanics,
the ``quick-condition'' is usually described as a liquefaction due to
high water pressure essentially possible with any soil. However,
previous studies have detected anomalous rheological properties from
natural quicksand. Pushed by these contradicting points of view we set
off to Len double dagger ois Maranhenses in North-East Brazil, where
quicksands are common, to investigate rheology and strength in situ. We
found that along very quiet drying lakes cyanobacteria cement an
impermeable crust above a suspension of grains. Beyond a critical
pressure, the crust fails releasing water from the collapsing colloidal
structure and radically changing the depth dependence of the shear
strength from a constant to a linear function. The sedimenting solid
fraction and the rapid increase of shear strength can indeed trap an
intruder endangering his life if the basin is sufficiently deep. As
opposed to some previous studies, we find that this quicksand condition
cannot be restored once it has collapsed. Finally, we also show some
preliminary results from a contact dynamics model specially designed to
mimic the living quicksand behavior.
Tags
- biomaterial}
- collapsible
- contact
- distinct
- dynamics;
- element
- matter;
- method;
- quicksand;
- simulations;
- soil;
- {granular
