A Procedure for Determining Rock-Type Specific Hoek-Brown Brittle Parameter s

  • F. T. Suorineni
  • D. R. Chinnasane
  • P. K. Kaiser
Original Paper


The Hoek-Brown failure criterion constants m and s are equivalent rock friction and cohesion parameters, respectively. On the laboratory scale, m depends on the rock type and texture (grain size), while s = 1 for all rocks. On the field scale, m is a function of rock type, texture, and rock mass quality (geological strength index, GSI), while s is simply a function of rock mass quality. The brittle Hoek-Brown damage initiation criterion (m-zero criterion) is a modification to the conventional Hoek-Brown failure criterion with m = 0 and s = 0.11. The m-zero damage initiation criterion has been shown to better predict depths of failure in excavations in some moderate to massive (GSI ≥ 75) rock masses, but over predicts depths of failure in other rock types. It is now recognized that the Hoek-Brown brittle parameter (s) is not the same for all hard, strong, brittle, moderate to massive rock masses, but depends on the rock type. However, there are no guidelines for its determination for specific rock types. This paper presents a semi-empirical procedure for the determination of rock-type specific brittle Hoek-Brown parameter s from the rock texture, mineralogical composition, and microstructure. The paper also differentiates between brittle and tenuous rocks. It is shown that, while the use of the term ‘brittle’ is appropriate for rock mechanical excavation and mode of failure in weak rocks with limited deformability, it is inappropriate for use in explaining the difference in resistance to stress-induced damage in different rock types, and can cause confusion. The terms ‘tenacity/toughness’ are introduced to describe rock resistance to stress-induced damage in excavation performance assessment, and a rock tenacity/toughness rating system is presented.


Hoek-Brown failure criterion Hoek-Brown brittle parameter Excavation stability Damage initiation Tenuous rock Rock tenacity rating index Depth of failure 

List of symbols

a, mb, and s

rock mass constants


major principle stress (MPa)


minor principle stress (MPa)


intact rock uniaxial compressive strength (MPa)


intact rock tensile strength (MPa)


friction angle (°)


cohesive strength (MPa)


geological strength index


intact rock material constant


damage factor


stress level


depth of failure


strain-based brittleness index


plastic strain


accumulated plastic strain at frictional strength mobilization


accumulated plastic strain at cohesion loss


normal stress


constant that depends on the rock mineralogical composition, texture, structure, metal content, etc.


strength reduction factor


texture coefficient


individual value of the rock property (e.g., strength or modulus)


mean of the individual rock property (e.g., mean strength or modulus)


Weibull shape parameter (homogeneity index)




tunneling quality index


damage initiation stress threshold


damage coalescence stress threshold


acoustic emission


rock tenacity rating index


stiffness heterogeneity factor


percentages of the various minerals present


stiffnesses of the minerals


weighted average stiffness


weighted total average stiffness


heterogeneity index


harmonic mean


rating of stiffness heterogeneity factor


grain size rating factor


foliation index


foliation strength anisotropic index


foliation rating factor


rock mass strength ratio



This work was funded by the Natural Sciences and Engineering Research Council (NSERC) of Canada and the Canadian Mining Industry Research Organization (CAMIRO). The authors wish to thank Mr. Charles Graham for his support. We also wish to thank the other staff of the Geomechanics Research Centre (GRC) who contributed in various ways during the research. The contribution of previous GRC staff and partners are also acknowledged, in particular, the contributions of Dr. John Henning, Dr. Hajiabdolmajid, and Dr. Mark Diederichs are highly appreciated.


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Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • F. T. Suorineni
    • 1
  • D. R. Chinnasane
    • 2
  • P. K. Kaiser
    • 1
  1. 1.MIRARCO Mining Innovation/Geomechanics Research CentreLaurentian UniversitySudburyCanada
  2. 2.School of EngineeringLaurentian UniversitySudburyCanada

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