Size and shape effects in point load tests of irregular rock fragments

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Department of Geological and Mining Engineering and Sciences


Point-load tests were performed on three hard rocks of the Lake Superior district, ironformation, metadiabase, and ophitic basalt. More than 500 irregular, mine-run fragments ranging in diameter up to about 250 mm were tested in the field, using a specially designed, semi-portable test rig. Results were analyzed by multiple regression techniques, seeking a "best" expression for the point-load strength in terms of a size effect and shape effects. Standard unconfined compression tests and "Brazilian" tests were also performed on the metadiabase and the basalt, three core sizes of each, in order to determine their respective size effects. The size-effect exponents for compression were found to be a variable characteristic of rock type, as previously reported for other rocks by the senior author, whereas the size-effect exponent in the point-load test was constant over all three rocks.

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© 1992 Springer-Verlag. Publisher’s version of record:

Publication Title

Rock Mechanics and Rock Engineering