A comparison of methods for determining m_i the Hoek-Brown parameter for intact rock material

摘要

The intact rock constant, m_i is one of the three basic input parameters required for the widely used Hoek-Brown failure criterion. In the absence of laboratory testing, guideline charts with m_i values based on rock type have been provided by Hoek & Brown and others. Our analysis of existing databases on rock material properties (such as Sheorey, Douglas and Rocscience) demonstrates that there is a very poor correlation between lithology and m_i values. The databases, together with the results of further uniaxial, triaxial and tensile laboratory testing, have been used to assess the relationship between the ratio of uniaxial to tensile strength (R) and m_i. The paper concludes that the most accurate method of assessing m_i values remains as statistical analysis of data from a full set of triaxial tests plus tensile tests. In the absence of such testing, the use of R as a means of estimating m_i is considered to be a preferable alternative to relying on guideline charts.