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Abstract Rocks are heterogeneous and have scattered test results for strengths due to the differences among specimens. The strength criterion fitted to test data describes merely an average effect of the confining pressure on the rock’s strengths. The experimental results within the confining pressure of 100 MPa revealed that the dispersion of the strengths resulted from the fissures or cracks in the specimens decreased as the increasing of the confining pressure. The two parameters in the exponential criterion to describe the effect of confining pressure on strengths were found to be material-dependent and not influenced by the other factors of specimens. The uniaxial compression strengths(UCS) of specimens may be calculated from the triaxial strength under confining pressure using the exponential criterion. The strengths of the granite specimen of small size under the high confining pressure were scattered greatly because the respective contents of the quartz，the feldspar and the mica were different in each specimen. Besides，the ends effect of friction affected the strengths of the granite specimen due to the occurrence of large lateral deformations under the high confining pressure.
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Received: 03 August 2013
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2014, Vol. 33 
