Geology Reference
In-Depth Information
influence the values of the cohesion and, possibly, the friction parameters if the
fluid is chemically active, as may well be the case if it is water.
If clays are present, it may be relevant, further, to distinguish between ''free''
pore water and adsorbed water (for example, Bombolakis et al.
1978
).
7.2.5 Effect of Temperature: Creep
In the cases of pure particulate flow and of cataclastic granular flow the relative
movement of the granules can be expected to be generally rather insensitive to
temperature because of the relatively temperature-insensitive natures of the pro-
cesses of friction and fracture. However, there are some temperature effects that
can be measured and that can be of practical importance, and there is scope for
additional temperature effects in the case of cohesive granular flow.
In general, there are two ways in which a deformation mechanism can be
affected by a change in temperature. On the one hand, insofar as the process
involves the local elastic distortion of the crystal structure, it will tend to depend
on temperature in the way in which the elastic modulus depends on temperature,
and no time-dependent or rate effects need be involved. On the other hand, insofar
as the process involves the local disruption of the atomic bonding structure, it is
likely to depend on thermal activation and so a time or rate dependence will be
involved; in this case, the process will be characterized as a thermally-activated
one and the possibility of creep or strain rate effects arises. The effects that we
shall discuss in this section will be mainly of this second type.
In the case of models of pure particulate flow, the main physical parameter is
the friction, and so temperature and time effects would be expected to have their
origin in the temperature and sliding rate sensitivities of friction, which are gen-
erally relatively small. There are three main physical models for the origin of
friction (Paterson and Wong
2005
,
Sect. 8.4.3
):
(1) The adhesion theory of Bowden and Tabor (
1950
;
1964
), which is based on the
local plastic deformation of welded or adhering junctions.
(2) The dilatational work theory according to which the irreversible work done
against the normal load through the dilatational component of the displace-
ment (references in Paterson and Wong
2005
,
Sect. 8.4.3
)
.
(3) The asperity fracture theory of Byerlee (
1967
) based on the local brittle
fracture of interlocking asperities.
The asperity fracture model is probably the more widely applicable to rocks, at
least at low to moderate temperatures, and in this case the temperature and time
dependence would be similar to that for brittle fracture in rock and so be relatively
unimportant (Paterson and Wong
2005
,
Sect. 3.4
). However, there may be some
high temperature or other situations in which the component minerals can readily
deform plastically and in which the adhesion model of friction is therefore more
relevant; temperature and time effects similar to those for plastic deformation
