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To determine the constitutive properties of the components in a rock structure, triaxial tests are commonly carried out on cylindrical test specimens. The conventional triaxial test (designated the single-stage triaxial test) involves obtaining a peak strength for the specimen and, after its breakage, a residual strength. In the multistage triaxial test, however, several peak and residual strengths can be obtained from a single specimen. This technique enables the experimenter to conserve samples and to obtain more consistent strength data by eliminating sample variabilities for the construction of failure envelopes. The feasibility of this test is examined by comparing strength results for single-stage and multistage tests in terms of the cohesion and the friction angle, which are calculated from the failure envelopes constructed by the two different types of test data. The feasibility is confirmed for Pierre shale and Raton shale, but is doubtful for Lyons sandstone, which is very brittle.

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