Rock Strength Tests
Two
main types of tests that measure rock strength
are the unconfined compressive test and the triaxial
test. Another test used is the direct shear
test, but it will not be discussed here as it is
uses soil, rather than rock, samples. You can
find description of that particular test here.
Unconfined Compressive
Test
In this type of test, only a vertical force
is applied to the sample until it undergoes
failure.
Unconfined Compressive Test
Apparatus
http://osp.mans.edu.eg/geotechnical/Ch1C.htm
At the failure
point, we can construct the diagram below. Note
that one of the principal stresses is equal to
zero.
Unconfined Compressive Test Results
http://osp.mans.edu.eg/geotechnical/Ch1C.htm
A
shortcoming of this test is that it is not
representative of actual conditions. This is
easily apparent, because only axial force is
simulated in this experiment.
Triaxial Test
This
test is more realistic than the unconfined
compressive test, since it experiences more
than just axial force. The test is repeated
several times so several Mohr circles can be
constructed. Then, the shear strength of the
material can be determined.
