Anisotropy and
70 inhomogeneity
10.1 Rock masses: order and disorder
”The use of laboratory tests to predict the reaction of a rock massif
encounters three major and inter-related obstacles. The first of these is
the frequent reluctance of the user to recognize and accept the fact that
rock is a heterogeneous material. It seldom is isotropic; it very often
acts as an anelastic medium; it rarely occurs as a continuous medium.
And, all too frequently the rock in situ may have natural stresses that
cannot be quantitatively examined and thus cannot be simulated in the
laboratory. The second major obstacle is that as yet we have no way
to quantitatively assess the influence of gross geological defects such as
faults, joints, fractures, folds, etc. Thus we are unable to simulate their
effects in laboratory testing.”
From the information and philosophy presented so far in this book,
the text in the paragraph above follows naturally and might have been
written recently. In fact, it was the beginning of an article (Judd, 1965 l)
by William Judd published in 1965. It is evident that the problems in
engineering rock mechanics have been recognized for a long time and we
hope that the same paragraph will not still be appropriate in, say, 2065.
We have seen in the previous chapters that a rock mass is a complex geo-
metrical and mechanical assemblage. Although specific physical mechan-
isms have created the rock mass in the form we see today, it is difficult
to sample and characterize the geometrical and mechanical complexity
resulting from the superimposition of a sequence of geological processes.
From the engineering point of view, there are two crucial aspects:
(a) we should be aware of this rock mass complexity; and
(b) we should find ways to characterize the rock adequately for engineer-
Generally, it is not necessary to interpret the nature of the present-day
rock mass in order to understand exactly which mechanisms left their
ing purposes.’ Judd W. R. (1965) Some rock mechanics problems in correlating laboratory results
with prototype reactions. Int. J. Rock Mech. Min. Sci., 2,197-218.