Laboratory Tests - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 409

The preparation of specimens should be carried out by means of drilling, cutting, turning
or grinding. The ends of the specimen must be coplanar with a maximum tolerance of
±

0.1 mm. The axis and the end faces of the specimen must form a right angle with a
maximum tolerance of 0.05°. Hardening materials to compensate for the unevenness

of the end faces (e.g. epoxy) should only be used if the end faces cannot be prepared
with sufficient accuracy (DGGT 2004b).
As test apparatus a testing machine with a force measuring device according to accepted
national requirements should be used. The specimen is placed between a lower platen
(base platen) and an upper platen (loading platen) of the testing machine (Fig. 14.1). In
order to be able to compensate for potential deviations from plane parallelism, at least one
of the two platens must be spherically seated (ISRM 1979a, ISRM 1999a, DGGT 2004b).

±

Figure 14.1 Test apparatus for uniaxial
compression tests (WBI Company)

Conventionally, the specimen is axially loaded with a force F at constant axial strain
rate until failure. The duration of the test should not be less than 5 minutes. The axial
strain rate should be selected accordingly (DGEG 1979a, DGGT 2004b). Also, a load-
ing at constant stress rate should be possible (ISRM 1979a, DGGT 2004b).

The strains of the specimen should be recorded continuously during the test and plotted
as stress-strain curves. Measurement of axial strain ε t in the

middle part of the specimen is recommended. Normally strain gauges are glued onto
the lateral surface of the specimen. The axial strain

ε a and tangential strain

ε a is measured by strain gauges that
are arranged vertically in the direction of loading. The tangential strain ε t is measured