Laboratory Tests - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 432

The thin cylindrical disk-shaped specimen with thickness T and diameter D is placed
between the two platens and then the force F is applied to the specimen by the rectangu-
lar punching block (Fig. 14.16). F is gradually increased until failure takes place and the
failure load Ff f is recorded. The test can be recognized as valid if the specimen is broken
into three parts, the two ends that are fi xed in the apparatus and the middle part of the
specimen that is punched out (Fig. 14.16, below). Otherwise the test should be rejected
as invalid (ISRM 2001).
Figure 14.16 Block punch index test (ISRM 2001)
According to Sulukcu & Ulusay (2001), the number of invalid tests increases with in-
creasing thickness T of specimen. It is therefore suggested that specimens thicker than
T = 15 mm should not be tested.
The block punch strength index BPI (in MPa) is defi ned as follows (ISRM 2001):
(14.43)