MEASUREMENT OF ROCK ELASTIC-MODULI IN TENSION AND IN COMPRESSION AND ITS PRACTICAL SIGNIFICANCE

The moduli of deformation of rock in tension and in compression are generally assumed equal. However, many rocks show different deformation properties when loaded in tension and in compression. This property is usually referred to as bimodularity. In this paper, a new testing technique in which moduli in both tension and compression can be measured on the same specimen in the same compressive loading frame is described. Testing results from halite, potash, granite, and limestone indicate that moduli in compression and in tension are different for at least three of these materials. The new testing technique is validated against the standard uniaxial tension and uniaxial compression tests on potash and halite. Also, results from granite by the new testing technique are comparable with previously published data. The practical significance of rock bimodularity is discussed as well. It is demonstrated that this property significantly influences the deflection and stress distribution in a simple beam problem. Bimodularity also influences the interpretation of indirect rock tension test results and the prediction of roof deflection in underground openings. Ignoring bimodularity overestimates rock tensile strength in most of the indirect rock tension tests and underestimates roof deflection.