Resistencia del masiso rocoso

2003:16

TECHNICAL REPORT
Rock Mass Strength
A Review

Catrin Edelbro

Technical Report

Department of Civil Engineering
Division of Rock Mechanics

ISSN: 1402-1536 - ISRN: LTU-TR--03/16--SE

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PREFACE
This literature review is part of a joint research project between LKAB and Luleå
University of Technology. The financial support for the project is being provided by
LKAB,the LKAB Foundation, the Research Council of Norrbotten and Luleå
University of Technology. The research project is aimed at increasing the
understanding of the rock mass strength and to identify the governing factors, with
special application to hard rock masses. In this report, the result of a comprehensive
literature review of both intact rock and rock mass failure criteria and classificationsystems is presented.
I would like to thank my project reference group, as their support and many
suggestions of how to improve my work have been of great importance. This group
consists of Professor Erling Nordlund at the Division of Rock Mechanics, Luleå
University of Technology, Dr. Jonny Sjöberg at SwedPower AB, Mr. Per-Ivar
Marklund at Boliden Mineral AB and Tech. Lic. Lars Malmgren atLKAB.
Furthermore, special thanks must be given to Dr. Arild Palmström at Norconsult,
Norway, for his helpful and supportive discussions. I would also like to thank Mr.
Meirion Hughes for help in correcting the English.

Luleå, March 2003

Catrin Edelbro

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SUMMARY
The estimation of the rock mass strength is becoming more and more important as the
mining depths increase inSwedish mines. By a better understanding of the rock mass
strength it is possible to reduce stability problems that may occur due to deeper mining.
This review constitutes the first phase of a research project aimed at developing a
suitable method to estimate the hard rock mass strength.
One of the most common ways of determining the rock mass strength is by a failure
criterion. The existingrock mass failure criteria are stress dependent and often include
one or several parameters that describe the rock mass properties. These parameters are
often based on classification or characterisation systems. This report is a critical literature
review of failure criteria for intact rock and rock masses, and of classification/
characterisation systems. Those criteria and systems that arepresented were selected
based on the facts that they are published, well known, deemed suitable for
underground excavations and/or instructive. Totally eleven failure criteria for intact
rock, five for rock masses and nineteen classification/characterisation systems are
presented.
To decide which systems and criteria that are applicable for hard rock masses, some
limitations have been stated.The rock mass is assumed to be continuous, comprising of
predominantly high-strength rock types with a uniaxial compressive strength of the
intact rock in excess of 50 MPa and with a failure mechanism caused by compressive
stresses. The limitations for further studies of the classification/characterisation systems
are that they should present a result that is connected to the strength, give anumerical
value, have been used after the first publication and be applicable to hard rock masses.
Based on this study, it was concluded that the uniaxial compressive strength, block size
and shape, joint strength and a scale factor are the most important parameters that
should be used when estimating the rock mass strength. Based on these findings,
selected systems and criteria were chosenfor further studies. These include Rock Mass
Rating (RMR), Rock Mass Strength (RMS), Mining Rock Mass Rating (MRMR),
rock mass quality (Q-systemet), rock mass Number (N), Rock Mass index (RMi),
Geological Strength Index (GSI) and Yudhbir, Sheorey and Hoek-Brown criterion.
Keywords: Rock Mass, Strength, Failure Criterion, Classification, Characterisation

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