Authors: Dirk Kadau Hans J Herrmann José S Andrade Ascânio D Araújo Luiz J C Bezerra Luis P Maia
Publish Date: 2008/11/04
Volume: 11, Issue: 1, Pages: 67-71
Abstract
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 “quickcondition” 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 Lençois Maranhenses in NorthEast 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
Keywords: