Rock failure in compression

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1986

The long-term response to sustained compressive loading of two crystalline hard rocks of the Canadian Shield has been investigated. Static fatigue tests conducted on granite and anorthosite have shown that in a humid environment the long-term strengths of these crystalline igneous rocks could be less than 60 percent of their dry instantaneous strengths. Such reduction in strength has implications for the design and construction of deep tunnels, mines and other underground installations. The particular case of a nuclear fuel waste vault located at a depth of one kilometer is considered.

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Mining Technology, 2012

Many brittleness criteria have been proposed to characterise material behaviour under triaxial compression, but there is no consensus as to which criteria is the most suitable. It was shown recently that increasing σ3 can lead to contradictory intact rock behaviour within different ranges of σ3. For example, rock behaviour can be changed from Class I (ductile) to Class II (brittle) and then to Class I again, based on the Wawersik and Fairhurst (1970) classification. Brittleness in this case can vary from absolute brittleness to absolute ductility. In this paper, it is argued that only two of the many existing criteria can properly describe the variation of brittleness within a wide range of confinements. These criteria rely upon energy balance and are based on sound physics principles. 2 Brief analysis of brittleness criteria Rock brittleness is determined by different parameters obtained experimentally. These parameters can represent intrinsic material properties and also the loading conditions (e.g. the stiffness or elastic energy of the loading system). Brittleness indexes involving solely intrinsic parameters characterise the intrinsic material brittleness. Brittleness indexes based on ratios involving both intrinsic material parameters and https://papers.acg.uwa.edu.au/p/1201_22_tarasov/

In this study, a simple approach is introduced to formulate a rock failure criterion for interpreting rock failure problems. The proposed criterion can be considered as a modification of octahedral shear stress theory and its validity conditions to produce a simple general equation that provides a criterion for rock failure taking the anisotropic nature and directional properties of rocks into consideration. This criterion is based on eliminating some of the limitations or restrictions encountered in various rock failure criteria, using stress invariants as analytical parameters.

Proceedings of the International Conference on Deep and High Stress Mining

High stresses are expected in deep mines, and it is perhaps unusual for rock failure due to high stresses to be observed in shallow mining. In this paper, stress-induced failures of competent rock are described in three shallow mining situations. Two of the rock failures occurred with considerable violence, both involving significant strain bursting seismicity. Rock failures in the third case often occurred with some violence and were preceded by audible noises. The first situation is failure of very competent granite in a dimension stone quarry, in which the depth of the "vertical cut slope" was about 3 m. The second situation is failure of the roof in a coal mine at a depth of about 50 m below surface. The third situation is also failure of the roof in a coal mine, but at a depth of about 25 m below surface. None of these failures can be explained using commonly-used rock strength criteria.

Scientific Reports

A carbonate sample extracted from the depth of about 10 kft was subjected to uniaxial loading while the confining stress remained constant. Post-experiment inspection of the sample showed an inclined crack at an angle less than 20° to the horizontal. This subhorizontal crack orientation was contrary to the expected 45° inclination, the plane of the maximum shear stress. Coincidentally, as shown by CT-scan prior to loading, there was a boundary between two layers of different density inside the sample located almost exactly where the crack appeared. This density difference has arguably translated into the contrast in the elastic properties at the boundary. The hypothesis is that because of this elastic heterogeneity, an incipient crack developed at the boundary due to the unavoidable tensile stressing of the sample as it was brought to the benchtop from its original state of high confining stress at depth. Controlled uniaxial compression made the sample slip along this crack, which t...

International Journal of Rock Mechanics and Mining Sciences, 2013

Brittleness is one of the most important mechanical properties of rock; however, the concept of brittleness in rock mechanics is yet to be precisely defined. Many brittleness criteria have been proposed to characterise material behaviour under compression, but there is no consensus as to which criteria is the most suitable and reliable. This paper considers brittleness at compression as the rock capability to self-sustaining macroscopic failure in the post-peak region due to elastic energy accumulated within the loaded material. The applicability of various criteria for assessing rock brittleness from this point of view is analysed. It is shown that only two of many existing criteria can describe properly the intrinsic material brittleness within the whole range of brittleness variation from the absolute brittleness to ductility. These criteria rely upon post-peak energy balance and are based on sound physics principles. Unlike other existing criteria they allow for the representation of two classes of rock behaviour (Class I to Class II) in the form of continuous, monotonic and unambiguous scale of brittleness. The effect of confining pressure on rock brittleness is analysed where rock behaviour can be changed from Class I to Class II and then to Class I again.

Ausrock , 2018

For most practical rock engineering purposes, stress versus strength conditions around underground openings for which rock masses fail and their various modes of failure, are reasonably well-understood and predictable. Some rock masses and particular rock types fail slowly and relatively quietly. However, others can fail rapidly, violently and maybe with the ejection of significant broken rock. In some countries and in some mines, the latter style of violent fracturing and failure of the rock mass is referred to as ‘strain bursting’. It can be alarming and extremely hazardous to nearby miners and machines. For such situations, the design and installation of appropriate ground support, to provide a safe work place, can be challenging. At any particular mine site, it’s often generally understood which local rock masses (rock types) are prone to strain bursting. Competent and strong siliceous rocks and some massive sulphides are often the main offenders. While some neighbouring, equally-competent and strong rocks might also fail, they do so more quietly and without ejection. To understand this contrast, a better understanding of the fracturing process is required other than simple and standard strength versus stress considerations. Suites of standard intact rock properties from numerous Australian mines have been used to define and help understand different high-stress failure styles for component intact rock; especially those prone to violent fracturing (strain bursting). Simple considerations of micro-fracturing (defects in the intact material), plus the available energy at failure versus the energy consumed during fracturing, distinguishes between over-stressed and competent rock types that fracture violently and those that don’t.

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Stavební obzor - Civil Engineering Journal, 2019

The contribution is focused on investigation of strains in a rock specimen during uniaxial compression test. Three components of strain occur in cylindrical shape specimen: axial, radial and volumetric. Determination of the strains is possible by using of local sensors. Strain gauges fixed on specimen surface were used in this study. Axial and radial components of strain were measured directly, and volumetric strain was calculated. Two types of rock were tested, syenite and sandstone, to illustrate variability of strain behaviour of rocks. Strain measurement is necessary for determination of Young's modulus and Poisson's ratio. Moreover, early states of failure can be identified by volumetric strain which is considerably sensitive to failure states.