Geology Reference
In-Depth Information
Chapter 7
Deformation Mechanisms: Granular Flow
7.1 Basic Concepts: Kinematics, Compatibility, Dilatancy
7.1.1 Introduction
In the previous two chapters we have considered deformation processes that
involve the relative movement of individual atoms or molecules (
Chap. 5
)orof
on deformation mechanisms we shall consider flow by the relative movement of
more or less macroscopic entities, which may be whole grains or groups of grains
such as particles of fractured rock. These entities can perhaps best be referred to
generically as granules and their assemblage be said to constitute a granular body.
The flow by relative movement of granules can then be called granular flow.
In considering the mechanisms of granular flow we shall take the somewhat
unusual step of treating, under this same heading, both the nearly temperature
independent phenomena of low temperature particulate and cataclastic flow and
the strongly temperature sensitive phenomena of high temperature granular flow
(''superplasticity'') involving viscous or other accommodation processes. This
approach derives from the view that the underlying kinematics of all these pro-
cesses are similar, being based on the relative movement of granules as entities,
even though the dynamics or rate control may depend on widely different pro-
cesses, ranging from local friction or fracturing to atomic diffusion. The concern of
this chapter will be with the various mechanisms of granular flow and no attempt
will be made to expound the macroscopic flow theory, which is part of continuum
mechanics.
The granules involved in the flow of the granular material are understood to be
entities that persist identifiably for at least the duration of the deformation incre-
ment being considered. However, they may undergo some gain or loss of sub-
stance by diffusive exchange or fracturing, or they may themselves undergo
deformation. They are described above as being macroscopic only in the sense of
