Evaluation of Methods for Determining Crack Initiation in Compression Tests on Low-Porosity Rocks
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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.
KeywordsCrack initiation Lateral strain response Uniaxial compressive strength Spalling
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.
- Brown ET (ed) (1981) Rock characterization, testing and monitoring, ISRM suggested methods. Pergamon Press, OxfordGoogle Scholar
- Cook NGW (1963) The basic mechanics of rockbursts. J South Afr Inst Min Metall 63:71–81Google Scholar
- Fairhurst C, Cook NGW (1966) The phenomenon of rock splitting parallel to the direction of maximum compression in the neighbourhood of a surface. In: Proceedings of the 1st congress of the international society of rock mechanics, Lisbon, pp 687–692Google Scholar
- Glamheden R, Fälth B, Jacobsson L, Harrström J, Berglund G, Bergkvist L (2010) Counterforce applied to prevent spalling. Technical Report TR-10-37, Swedish Nuclear Fuel and Waste Management Co, Stockholm, SwedenGoogle Scholar
- Griffith AA (1921) The phenomena of rupture and flow in solids. Philos Trans R Soc Lond 221A:163–198Google Scholar
- Griffith AA (1924) Theory of rupture. In: Biezeno CB, M BJ (eds) Proceedings of the first international congress on applied mechanics, Delft, Tech. Boekhandel en Drukkerij J Walter Jr, Delft, pp 55–63Google Scholar
- Hardy HR (1981) Applications of acoustic emission techniques to rock and rock structures: a state of the art review. In: Drnevich G (ed) Acoustic emission in geotechnical engineering practice, ASTM STP750, pp 4–92Google Scholar
- Hoek E, Brown ET (1980) Underground excavations in rock. The Institution of Mining and Metallurgy, LondonGoogle Scholar
- Janson T, Ljunggren B, Bergman T (2007) Modal analysis on rock mechanical specimens. Specimen from borehole KLX03, KLX04, KQ0065G, KF0066A and KF0069A. Oskarshamn site investigation. SKB P-07-03, Swedish Nuclear Fuel and Waste Management Co., Stockholm, SwedenGoogle Scholar
- Murrell SAF (1963) A criterion for brittle fracture of rocks and concrete under triaxial stress, and the effect of pore pressure on the criterion. In: Fairhurst C (ed) Proceedings of the 5th U.S. symposium on rock mechanics, Pergamon Press, New York, pp 563–577Google Scholar
- Walpole RE, Myers RH, Myers RH, Ye K (2002) Probability & statistics for engineers & scientists, 7th edn. Prentice Hall, Upper Saddle RiverGoogle Scholar