Studying the effect of non-spherical micro-particles on Hoek-Brown strength parameter mi using numerical true triaxial compressive tests

Qi Zhang, He Hua Zhu, Lianyang Zhang

Research output: Contribution to journalArticlepeer-review

19 Scopus citations


The strength parameter mi in the Hoek-Brown strength criterion is empirical and was developed by trial and error. To better understand the fundamental relationship between mi and the physical characteristics of intact rock, this paper presents a systematic study of mi by representing intact rock as a densely packed cemented particle material and simulating its mechanical behavior using particle flow modeling. Specifically, the three-dimensional particle flow code (PFC3D) was used to conduct numerical true triaxial compression tests on intact rock and to investigate the effect of non-spherical micro-particle parameters on mi. To generate numerical intact rock specimens containing non-spherical micro-particles, a new genesis process was proposed, and a specific loop algorithm was used based on the efficiency of the process and the acceptability of generated specimens. Four main parameters-number, aspect ratio, size, and shape-of non-spherical micro-particles were studied, and the results indicated that they all have great effect on mi. The strength parameter mi increases when the number, aspect ratio, or size is larger or the shape becomes more irregular, mainly as a result of the higher level of interlocking between particles. This confirms the observations from engineering experience and laboratory experiments. To simulate the right strength parameter mi, it is important to use appropriate non-spherical micro-particles by controlling these four parameters. This is further demonstrated by the simulation of two widely studied rocks, Lac du Bonnet granite and Carrara marble.

Original languageEnglish (US)
Pages (from-to)96-114
Number of pages19
JournalInternational Journal for Numerical and Analytical Methods in Geomechanics
Issue number1
StatePublished - Jan 1 2015


  • Hoek-Brown strength parameter m
  • Interlocking effect
  • Non-spherical micro-particles
  • Numerical true triaxial compressive test
  • Rock
  • Three-dimensional particle flow modeling

ASJC Scopus subject areas

  • Computational Mechanics
  • General Materials Science
  • Geotechnical Engineering and Engineering Geology
  • Mechanics of Materials


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