Engineering Rock Mechanics

174 Testing techniques

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,Reference mark

Figure 11.1 Access to the rock mass via a rock exposure (top), borehole core (mid-

dle) and the borehole wall (bottom-which is an image derived from video tape).

What about tests that can be conducted on a borehole wall? It is evident
that, apart from directly viewing the rock, the testing will usually consist
of indirect methods of assessing the rock mass properties-due to limita-
tions imposed by the borehole size. An example is shown in the lower part
of Fig. 11.1, where the dark sinusoidal wave indicates the trace of an
inclined discontinuity intersecting the borehole wall, being viewed via the
rotating mirror of a borehole camera.
There are always constraints on resources, and so it is necessary when
optimizing the rock characterization procedures to consider the require-
ments and to choose the rock access method and testing techniques in
accordance with the engineering objective. Because there are many differ-
ent rock engineering objectives, there can be no standardized site
investigation. Individual tests can-and indeed should-be standardized,
but the total programme and number of tests cannot be specified
independently of the objective. For example, the information requirements
for designing a block caving mining operation and a radioactive waste
repository are different.

1 1.2 Tailoring testing to engineering

requirements

There are the three main methods of accessing the rock, and there are many

tests that can be conducted. The objective is to tailor the testing to the