Civil Engineering Reference
In-Depth Information
Figure 14.14
Requirements on size and
shape of specimens for
point load tests
Point load tests should be carried out on specimens at or close to s = 50 mm. If this should
not be possible, a minimum specimen width of w = 25 mm is required (Fig. 14.14). In
such cases a size correction must be carried out using the following formula (ISRM
1985):
(14.41)
in which
is the so-called “size correction factor” and I
S
(50) is the size-corrected point load
strength index defi ned as the value of I
S
that would have been measured in a test carried
out on a specimen with s = 50 mm.
The point load strength index of many intact rocks has been found to be linearly corre-
lated to the unconfi ned compressive strength:
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