![]() It is essential to accurately determine the brittle-ductile transition stress to derive reliable values for mi. This paper aims to investigate the link between brittle-ductile transition stress, uniaxial compressive strength and Hoek–Brown material constant (mi) for different kinds of rock. However, studies that consider information about the brittle-ductile transition, the criterion's range of applicability, how to determine mi, and how confining pressures affect mi's values are scarce. A proposed definition of the brittle-ductile transition is the transition pressure at which no loss in strength takes place. But no tension reduction takes place at high confining pressure. The stress drop is the variation between peak and residual values. Rocks deformed at low confining pressure are brittle, which means that after peak stress, the strength declines to a residual value established by sliding friction. Interestingly enough, there is significant differences in the predicted m i values using different methods, which is more probably due to the quantity and quality of data used in the statistical analysis. The obtained results proves that for different rock groups (igneous, sedimentary, and metamorphic rocks), R-index method provides the best fit with the experimental data among the others, and it is also independent of rock type. Additionally, based on rock types, new material constants are introduced for igneous, sedimentary, and metamorphic rocks. In order to fulfill this goal, a large number of data for different quasi-isotropic intact rock types from the literature were collected and statistically analyzed. This paper aims to thoroughly review the previously existing methods to calculate the value of m i and make comparison between the obtain results to propose the new material constants that provide the best fit with the experimental data. ![]() So far, different approaches such as rigidity index method (R-index), uniaxial compressive strength-based method, and tensile strength-based method, and the combination of these two methods (combination based method) have been proposed to calculate the value of m i. An accurate determination of Hoek–Brown constant m i is of great significance in the estimation of the failure criteria of brittle rock materials. ![]()
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