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

Nicksiar, Mohsen; Martin, C. Derek

doi:10.1007/s00603-012-0221-6

Cited by 296 publications

(99 citation statements)

References 25 publications

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“…C is calculated by two methods, VS (Volumetric Strain) based on Brace et al (1966) and LSR (Lateral Strain Response) based on Nicksiar and Martin (2012). Crack damage stress, σ cd , indicates the stress of maximum volumetric strain.…”

Section: Bridgeman 1949mentioning

confidence: 99%

Effects of Confining Pressure and Pore Water Pressure on the Strain Behavior and Deformation Property of Aji Granite under Triaxial Compression Test

Sawayama

Katayama

2016

Jour. Geol. Soc. Japan

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To investigate the effects of confining pressure and pore water pressure on the strain behavior and deformation properties of Aji granite, triaxial compression tests were performed at a constant strain rate ( . s ) under confining and pore water pressures of -MPa and -MPa, respectively. During the tests, axial and radial strains were measured by two biaxial strain gauges. The results revealed increases in maximum differential stress and onset of dilatancy with effective confining pressure. Young s modulus tended to increase with confining pressure and decrease with pore water pressure. However, Poisson s ratio remained nearly constant under these experimental conditions. Dilatancy is related to the formation of micro-cracks during deformation and is enhanced at low confining pressures under dry conditions. In contrast, it tends to be suppressed at a high pore water pressure (low effective confining pressure) under wet conditions. These results indicate that stress concentration at the crack tip can be relaxed by the presence of pore water. Moreover, water injection into the specimen during wet experiments rapidly increases at a stress level of ~ % maximum differential stress. This rapid increase can be attributed to the formation of a micro-crack network.

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Section: Bridgeman 1949mentioning

confidence: 99%

Effects of Confining Pressure and Pore Water Pressure on the Strain Behavior and Deformation Property of Aji Granite under Triaxial Compression Test

Sawayama

Katayama

2016

Jour. Geol. Soc. Japan

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“…Other researchers suggest that crack initiation related to the Kaiser effect (will be discussed later) can be used to establish the in-situ state of stress (Seto et al 1999). Nicksiar and Martin (2012) proposed that the ISRM (International Society for Rock Mechanics) suggested methods be revised to include procedures suitable for establishing the crack-initiation stress.…”

Section: Introductionmentioning

confidence: 99%

“…The methods for detecting crack initiation have utilized either the volumetric strain or the lateral strain (Brace et al, 1966;Bieniawski, 1967b;Lajtai, 1974;Stacey, 1981), and have been modified by various researchers (Martin and Chandler, 1994;Diederichs, 2007, Nicksiar andMartin 2012). It has been shown that crack initiation is difficult to identify from the volumetric strain method, particularly if the specimen already contains a high density of cracks.…”

Section: Introductionmentioning

confidence: 99%

“…It has been shown that crack initiation is difficult to identify from the volumetric strain method, particularly if the specimen already contains a high density of cracks. On the other hand, analysis of the laboratory tests revealed that the lateral strain versus axial strain is nonlinear and therefore applying this approach is problematic (Andersson et al 2009, Nicksiar andMartin, 2012). As a result a certain degree of subjectivity may be introduced by picking the cracking levels using lateral and volumetric strain curves.…”

Section: Introductionmentioning

confidence: 99%

“…Eberhardt et al 1998 tried to determine crack initiation stress thresholds of intact rocks by using a moving point regression technique to the stress-strain data and an examination of the changes in the acoustic event properties with loading. However, the insignificant AE activity in the crack initiation stages made it difficult to differentiate between the background noise and the cracking-source acoustic events (Nicksiar and Martin 2012). The objective of this paper is to demonstrate AE as a technique for detecting cracking levels in rocks.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Detection of Cracking Levels in Brittle Rocks by Parametric Analysis of the Acoustic Emission Signals

2015

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Determination of the cracking levels during the crack propagation is one of the key challenges in the field of fracture mechanics of rocks. Acoustic emission (AE) is a technique that has been used to detect cracks as they occur across the specimen. Parametric analysis of AE signals and correlating these parameters (e.g. hits and energy) to stress-strain plots of rocks let us detect cracking levels, properly. The number of AE hits is related to the number of cracks, and the AE energy is related to magnitude of the cracking event. For a full understanding of the fracture process in brittle rocks, prismatic specimens of granite containing pre-existing flaws have been tested in uniaxial compression tests, and their cracking process was monitored with both AE and high-speed video imaging. In this paper the characteristics of the AE parameters and the evolution of cracking sequences are analyzed for every cracking level. Based on micro-and macro-crack damage, a classification of cracking levels is introduced. This classification contains eight stages 1) crack closure, 2) linear elastic deformation, 3) micro-crack initiation (white patch initiation), 4) micro-crack growth (stable crack growth), 5) micro-crack coalescence (macro-crack initiation), 6) macro-crack growth (unstable crack growth), 7) macro-crack coalescence and 8) failure.

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Investigation of microcracking behaviors in brittle rock using polygonal grain‐based distinct method

Wang

et al. 2021

Num Anal Meth Geomechanics

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The failure process in brittle rocks is an important topic in rock mechanics, whose good understanding assists in predicting the strength and deformation characteristics of rocks. Because it is difficult to directly observe microcracks in laboratory tests, a numerical model is a useful tool for investigating microcracking behaviors. However, the mechanism of microcrack evolution is still unclear at the grain scale considering the microscopic heterogeneities. This paper proposes a polygonal universal distinct element code grain‐based model to solve this problem. Compared with other grain‐based models, this model is different in that mineral grains are subdivided into polygon blocks. The grain size, composition, and bond types of the contacts are incorporated, and both inter‐ and intra‐grain cracks are mimicked. Subsequently, micro‐parameters of the blocks and contacts are carefully calibrated according to the laboratory results. Following this, the calibrated model is employed to study the microcracking behaviors of granite in unconfined compression, confined compression, and Brazilian splitting tests. Both the cumulative numbers and locations of microcracks in different grains are recorded, and the types of macroscopic fractures are identified. The modeling results show that tensile cracks dominate the generated microcracks in the low confined compression tests, and the macroscopic fracture pattern is axial splitting. Shear cracks are dominant in the high confined compression tests, and the macroscopic failure pattern is X‐type shear failure. The simulated results are consistent with those observed in the laboratory tests, and thus, may assist in improving rock acoustic emission monitoring and understanding the damage process of rock.

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

Cited by 296 publications

References 25 publications

Effects of Confining Pressure and Pore Water Pressure on the Strain Behavior and Deformation Property of Aji Granite under Triaxial Compression Test

Effects of Confining Pressure and Pore Water Pressure on the Strain Behavior and Deformation Property of Aji Granite under Triaxial Compression Test

Detection of Cracking Levels in Brittle Rocks by Parametric Analysis of the Acoustic Emission Signals

Investigation of microcracking behaviors in brittle rock using polygonal grain‐based distinct method

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