ABSTRACT: Various types of brittleness measures have been proposed in the past twenty years or so. These are usually aimed at describing, in a relative manner, the potential for a rock to collapse suddenly when loaded up to its ultimate strength. One of these measures is the Brittleness Index Modified (BIM), which was developed by the authors as a variant to the well known Wet index. In this paper, the authors first introduce some of the basic ideas behind the BIM. An empirical relationship is then developed between the BIM value and the ratio of the pre-peak modulus over the post-peak modulus, based on a large number of uniaxial compression test results on igneous rocks. Also, using an extended data base on over 50 different types of rocks of various origins, the authors propose some critical BIM values that can be used to evaluate, in a preliminary manner, the bursting liabilities of highly stress rock around underground excavations.

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