A procedure for determining rock-type specific hoek-brown brittle parameter s

F. T. Suorineni, D. R. Chinnasane, P. K. Kaiser

Research output: Contribution to journalArticlepeer-review

26 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)849-881
Number of pages33
JournalRock Mechanics and Rock Engineering
Issue number6
Publication statusPublished - Jan 1 2009
Externally publishedYes


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

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Geotechnical Engineering and Engineering Geology
  • Geology

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