The Brazilian test is one of the most established techniques used for indirect measurement of rock tensile strength. When the test is applied to soft to medium strength rocks, the rupture mechanism is always through the formation of a single diametrical crack initiated at the centre of the disc, where the induced tensile stress is the maximum. However, when applied to disc specimens of harder, stiffer and brittle rocks, secondary shear fractures often interfere adversely with the diametrical (characteristic) tensile crack in the Brazilian test. To prevent such undesirable shear cracking, a series of Brazilian tests on specimens of different sizes was carried out with four different brittle rocks, including granite, basalt and two types of monzonite. From the results, it is concluded that the problem associated with the undesirable shear failure developed in the vicinity of the contact points can be effectively eliminated through a change in the size of the disc in the Brazilian test.

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