Posted on November 03, 1999 at 16:25:01:

In Reply to: Mud Rush phenomina - solid/plastic transisition in ore passes posted by Phil Lovering on November 01, 1999 at 21:55:13:

Dear Mr. Lovering,

This is a long shot. It may or may not be of help.

In soils mechanics their is the phenomenon of quick clays. These are clays that are very solid and stable in-situ but when disturbed, say by heavy machinery, they liquify and run like mud. There instability is often linked to their geoligic history. Stabalizing chemicals have been leached out of these clays. This is well known in the Scandanavian countries where undersea clays have uplifted and the salt has been leached out over geolgic time.

There is the story of the German tanks and equipment being bogged down during the invasion of the scandanavian peninsula. The Germans studied their history and were able to stabilize the ground by spreading salt ahead of their advancing equipment. ■

Posted on December 08, 1999 at 10:41:45:

In Reply to: Re: Mud Rush phenomina - solid/plastic transisition in ore passes posted by Joseph A. Dos Santos on November 03, 1999 at 16:25:01:

Liquifraction of wetted particulate materials is not uncommon in the transport of ores. Similar changes of state occur in the 'working' of centrifuged materials and filter cakes and other damp powders. 'Quick clay' is a related phenomenon in soil mechanics and the infamous Abervan disaster took place when a spoil heap was infiltrated by excess water. In each case the capacity of the fluid to fully occupy the voidage space in the bulk relieves the particle to particle contact pressures and allows the material to behave as semi-fluid, of highly variable viscosity according to the degree of freedom of the particles to rearrange and shear within the fluid media.

Warren Spring Laboratories published wome work on the safe transportable moisture content for ores, following an investigation into the sinking of vessels made unstable by the settlement of bulk cargo to the extent that the moisture occupied the voidage and allowed the rolling of the vessel to move the cargo. Air entrainment or injection produces flushing and flooding by similarly displacing the particles from intimate contact pressures.

The problem of evaluating this behaviour is that the nature of the particle structure, and how this may re-arrange to higher densities, has a high bearing on the materials stability. For example clays have a plate-like form and can therefore be stable under load at a particular moisture content, until an applied shock re-alignes the particles from a random to a more parallel arrangement. ■