Implementation of a Flaw Model to the Fracturing Around a Vertical Shaft

Steen, Brecht; Vervoort, André; Napier, J.A.L.; Durrheim, Raymond

doi:10.1007/s00603-002-0040-2

Cited by 16 publications

(4 citation statements)

References 29 publications

(23 reference statements)

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“…Brittle rock is in nature a heterogeneous material which can be described by its internal microstructure. Micromechanical observations made during compression loading [ Hallbauer et al , 1973; Olsson and Peng , 1976; Kranz , 1983] have indicated that fracture initiation and fracture growth in brittle rock are to a large extent influenced by the presence of microstructure that introduces a heterogeneity in the stress distribution at the grain scale [ Van de Steen et al , 2003]. A key role of heterogeneity appears to be the creation of local concentrations of tensile stress, even when the rock as a whole is subjected only to compressive stress [ Gallagher et al , 1974; Blair and Cook , 1998a, 1998b].…”

Section: Introductionmentioning

confidence: 99%

Effect of heterogeneity of brittle rock on micromechanical extensile behavior during compression loading

Lan¹,

Martin²,

Hu³

2010

J. Geophys. Res.

381

156

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[1] A grain-based Universal Distinct Element Code model was developed to generate a deformable polygonal grain-like structure to simulate the microstructure of brittle rock. It takes into account grain-scale heterogeneity including microgeometric heterogeneity, grain-scale elastic heterogeneity, and microcontact heterogeneity. The microgeometric heterogeneity can be used to match the grain size distribution of the rock. The discrete element approach is able to simulate the microheterogeneity caused by elastic variation and contact stiffness anisotropy. The modeling approach was evaluated using Lac du Bonnet granite and Ä spö Diorite. The microheterogeneity played an important role in controlling both the micromechanical behavior and the macroscopic response when subjected to uniaxial compression loading. The crack-initiation stress was found to be controlled primarily by the microscale geometric heterogeneity, while the microcontact heterogeneity controlled the strength characteristics. The effect of heterogeneity on the distribution and evolution of tensile stresses and associated extension cracks was also examined.Citation: Lan, H., C. D. Martin, and B. Hu (2010), Effect of heterogeneity of brittle rock on micromechanical extensile behavior during compression loading,

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Section: Introductionmentioning

confidence: 99%

Effect of heterogeneity of brittle rock on micromechanical extensile behavior during compression loading

Lan¹,

Martin²,

Hu³

2010

J. Geophys. Res.

381

156

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“…However, more and more discontinuum models are being used. They show that incorporating flaws or weaknesses in the model has an important effect on when fractures are induced around a circular opening, both at the laboratory scale (e.g., [38,48]) and in situ (e.g., [58]).…”

Section: Discussion: Consequences Of Results Obtainedmentioning

confidence: 99%

Different Stress Paths Lead to Different Failure Envelopes: Impact on Rock Characterisation and Design

Vervoort

2023

Applied Sciences

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The strength of rock is a non-intrinsic property, and this means that numerous parameters influence the strength values. In most laboratory experiments, specimens are free of stress at the start of the tests, and the load is increased systematically until failure occurs. Around excavations, the opposite path occurs, i.e., the rock is in equilibrium under a triaxial stress state and at least one stress component decreases while another component may increase. Hence, the stress paths in classic laboratory experiments are different from the in situ stress paths. In the research presented, a first step was made to evaluate with an open mind the effect of these different stress paths on the failure process and failure envelope. The research was based on distinct element models, allowing the simulation of micro-fracturing of the rock, which is essential to correctly model rock failure. The micro-fracturing when loading rock (from zero or low stress state) until failure was different from the micro-fracturing when unloading rock (from the in situ stress state) until failure. And, hence, by this difference in weakening processes, the failure envelopes were significantly different. The conventional loading resulted in the largest strength and, thus, overestimated the rock strength in comparison to the real in situ behaviour. This finding, after being confirmed by further lab experiments, will have a direct effect on how one characterises rock material and on the design of rock excavations.

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“…This statement clearly is supported by the numerous research projects that are still being conducted that focus on the basic type of loading applied in laboratory experiments. These projects often focus on a specific aspect, for example, the impact of heterogeneities (e.g., [10,27,28]), the orientations of flaws or weak planes (e.g., [21,[29][30][31]), and the characterisation of the (micro-)fracturing process by the analysis of acoustic emission signals (e.g., [15][16][17]32,33]). These are only a few of the many examples that use classic testing procedures.…”

Section: Discussionmentioning

confidence: 99%

In Situ Stress Paths Applied in Rock Strength Characterisation Result in a More Correct and Sustainable Design

Vervoort

2024

Sustainability

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Rock strength is an essential parameter in the design of any underground excavation, and it has become even more relevant as the focus increasingly shifts to sustainable excavations. The heterogeneous nature of rock material makes characterising the strength of rocks a difficult and challenging task. The research results presented in this article compare the impact on the strength when the classic stress paths in laboratory experiments are applied versus when in situ stress paths would be applied. In most laboratory experiments, the rock specimens are free of stress at the beginning of the tests, and the load is increased systematically until failure occurs. Opposite paths occur around an underground excavation; that is, the rock is in equilibrium under a triaxial stress state and at least one stress component decreases while another component may increase. Based on discrete element simulations, the research shows that different stress paths result in different failure envelopes. The impact of this finding is evaluated in the application of wellbore stability (e.g., the minimum or maximum mud weight), whereby it is concluded that failure envelopes, based on stress paths closer to the in situ stress paths, result in a more accurate design. Although the most critical location along the circumference is not different, the required density of the mud is significantly different if the rock strength criteria are based on the more realistic in situ stress paths. This means that a change in the way the strength of rocks is characterised improves the sustainable design of all underground excavations.

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Implementation of a Flaw Model to the Fracturing Around a Vertical Shaft

Cited by 16 publications

References 29 publications

Effect of heterogeneity of brittle rock on micromechanical extensile behavior during compression loading

Effect of heterogeneity of brittle rock on micromechanical extensile behavior during compression loading

Different Stress Paths Lead to Different Failure Envelopes: Impact on Rock Characterisation and Design

In Situ Stress Paths Applied in Rock Strength Characterisation Result in a More Correct and Sustainable Design

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