ABSTRACT
Tensile strength of rock is an important parameter used in the design and stability analysis of underground structures. Rock tensile strength dictates the maximum roof span of underground openings, the maximum internal pressure of unlined storage caverns, the stability of boreholes under highly anisotropic stress states, and the borehole pressures for hydraulic fracturing. The direct tension test (ASTM D 2936) may not be applicable to high strength rocks due to the limited performance of the cementing adhesive between the loading platens and sample end surfaces. The Brazilian tension test (ASTM D 3967) has been widely used to obtain rock tensile strengths due to the simplicity of sample preparation and testing. It however can not provide the elastic parameters under pure tension. To overcome the strength limitation of the direct tension method Plinninger et al. (2004) propose the modified tension test to determine the rock strength under unidirectional condition. Even though their test method is simple, the results do not truly represent the direct tensile strength, and a measurement of the tensile elastic properties from the proposed specimen configurations is not possible.
