This paper presents the results of a series of biaxial compressive tests of granite cubes sizing of 75 mm, 100mm and 125 mm. Testing was done with a newly developed biaxial test apparatus, having a capacity of 500 metric tonnes in each direction and is equipped with servo-controlled load and displacement systems. Cubic samples tested biaxially exhibited a failure mechanism that is characterized by a varying degree of rock spalling, which is initiated at the free faces in the s1–s2 plane when the stress level reaches approximately sc/2 in both directions. An empirical biaxial failure is derived from a regression analysis of test results, and a new biaxial failure criterion for the jointed rockmass is proposed in an analogous way to the Hoek-Brown criterion, based on the test result and combining with GSI.

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