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Rock Mechanics and Rock Engineering

, Volume 45, Issue 4, pp 607–617 | Cite as

Evaluation of Methods for Determining Crack Initiation in Compression Tests on Low-Porosity Rocks

  • Mohsen NicksiarEmail author
  • C. D. Martin
Original Paper

Abstract

Laboratory testing of rocks is traditionally carried out to determine the peak strength using the ISRM Suggested Methods or other suitable standards. However, it is well known that in low-porosity crystalline rocks there are at least three distinct stages of compressive loading that can be readily identified if the stress–strain response is monitored during the loading process: (1) crack initiation, (2) unstable crack growth, i.e., crack coalescence and (3) peak strength. Crack initiation is noted as the first stage of stress-induced damage in low-porosity rocks, yet the suggested guidelines of the ISRM for compression tests make no mention of crack initiation. In addition, recent research suggests that crack initiation can be used as an estimate for the in situ spalling strength, commonly observed around underground excavations in massive to moderately jointed brittle rocks. Various methods have been proposed for identifying crack initiation in laboratory tests. These methods are evaluated using ten samples of Äspö Diorite and the results are compared with a simplified method, lateral strain response. Statistically, all methods give acceptable crack-initiation values. It is proposed that the ISRM Suggested Methods be revised to include procedures suitable for establishing the crack-initiation stress.

Keywords

Crack initiation Lateral strain response Uniaxial compressive strength Spalling 

Notes

Acknowledgments

We would like to acknowledge the financial contribution of Swedish Nuclear Fuel and Waste Management Company through the DECOVALEX Project. The authors would like to thank Lars Jacobsson (SP Sweden) for providing the stress–strain data for Äspö Diorite.

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Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  1. 1.Department of Civil and Environmental EngineeringUniversity of AlbertaEdmontonCanada

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