  A simple and popular constitutive model used to describe the compressional
strength of a consolidating strongly cohesive particulate gel is tested further
with new experimental data. Strong cohesive particulate gels have variously
been described as being ratchet (poro) elastic, on the one hand, and as having
a yield stress in compression, on the other, to the point where same groups of
workers have used both descriptions at one time or another. The dichotomy is
real though as such gels do show a hitherto somewhat puzzling elastic-plastic
duality. This can be explained in part by the strong concentration dependence
of the modulus since this leads to irreversible volumetric strain-hardening, in
effect, the ratchet; but only in small part. The real problem seems to be that,
until very recently, most work on consolidation has neglected what what
Michaels and Bolger told us to do over 50 years ago, viz. to take into wall
adhesion into account, most cohesive particulate gels being adhesive too. Since
wall adhesive failure is plastic in character, the simplest non-linear elastic
model of compressive strength can be combined with the simplest possible model
of wall debonding to produce a approximate complete constitutive description.
Examples of the use of such a description in detailed modelling of
consolidation equilibrium can be found in refs 10-12. Consolidation dynamics
with wall adhesion is a substantial modelling challenge remaining to be
tackled.
