Examining the Case for Accuracy and Precision When Determining the Hoek–Brown Parameters

The Hoek–Brown failure criterion has evolved from a pragmatic engineering tool into standard practice, yet its empirical foundations warrant renewed examination. This paper critically examines claims regarding "accurate" and "precise" determination of Hoek–Brown parameters (namely m_i, m_b, s, and GSI). In particular, while the criterion has proven useful over four decades, the foundational relationships for the m_b and s parameters were derived from limited laboratory-scale testing of Panguna andesite and have never been validated through systematic field-scale rock mass testing. Our analysis reveals important considerations. First, identical m_b values can arise from fundamentally different rock mass conditions, exposing a non-uniqueness problem. Second, GSI remains inherently qualitative despite attempts at quantification. Since m_b and s are calculated from GSI, pursuing precise m_i parameters cannot compensate for this fundamental uncertainty. Third, synthetic rock mass (SRM) modelling validates the Hoek–Brown framework while simultaneously indicating that m_i varies with fracture intensity, suggesting that for naturally jointed rock masses, m_i may not remain constant as conventionally assumed. Finally, the discussion examines how human factors facilitate the transition from "credible guide" to “established practice” and “standards” and how the use of AI tools risks amplifying unvalidated assumptions. The path forward requires transparency about empirical uncertainties, renewed field-scale validation, and recognition that computational sophistication cannot substitute for the reliable rock mass scale data that Hoek identified as critical components of rock engineering design.

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