A New Perspective on the Brittle–Ductile Transition of Rocks

Walton, Gabriel

doi:10.1007/s00603-021-02595-9

Cited by 25 publications

(8 citation statements)

References 87 publications

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“…In this way, the value of the BDT coefficient c (noted d in Walton, 2021) can be determined for individual rocks. Walton (2021) measured values of c between 0.9 and 6.8 for silicate rocks reported in the literature, while he obtained values between 2.1 and 10.7 for carbonates. The mechanical data collected by Walton can be plotted in strength versus confining pressure diagrams and show elongated, linear clusters of data points, well fitted by the expressions, σ 1 − σ 3 = 2.5 σ 3 and σ 1 − σ 3 = 3.5 σ 3 for silicates and carbonates, respectively (or, σ 1 − σ 3 = 2.4 σ 3 + 38 and σ 1 − σ 3 = 2.9 σ 3 + 82, if we remove the condition that the lines must pass through the origin).…”

Section: Discussionmentioning

confidence: 99%

Brittle Damage Processes Around Equi‐Dimensional Pores or Cavities in Rocks: Implications for the Brittle‐Ductile Transition

Bernabé,

Peč

2024

JGR Solid Earth

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In the Earth's upper crust, rocks deform mostly by means of brittle fracturing processes. At the micro‐scale these processes involve the formation and growth of microcracks in the vicinity of defects such as open fissures, pores and other cavities. Large defects can produce strong enough perturbations of the stress field to activate and/or intensify brittle damage around them. Here we considered the ideal cases of smooth cylindrical and spherical pores inside an infinite solid body subjected to remote triaxial compressive stresses (i.e., the intermediate and minimum principal stresses are assumed equal). We first established the resulting local stress field around one of those large pores and then verified whether certain brittle damage processes could be activated in these conditions. We mainly considered the formation of tensile microcracks and micro shear bands. The former requires the presence of tensile stresses in some regions around the pore, while the latter needs sufficiently large shear stresses on pre‐existing optimally inclined microcracks to overcome their frictional resistance to sliding. We find that shear driven deformation remains localized in the vicinity of the pore. On the other hand, dilatational, tensile cracks can propagate large distances away from the pore but cannot form at and above some threshold ratio of the least to the largest principal stresses. Faulting associated with interacting tensile cracks is therefore suppressed with increasing depth. Our analysis leads to conclusions generally consistent with published experimental observations and provides some clues to discuss the physical cause of the brittle‐ductile transition in rocks.

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Section: Discussionmentioning

confidence: 99%

Brittle Damage Processes Around Equi‐Dimensional Pores or Cavities in Rocks: Implications for the Brittle‐Ductile Transition

Bernabé,

Peč

2024

JGR Solid Earth

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“…Walton 29 analyzed the large database for different rock types. Based on his analysis, transition stress (σ TR ) depends on ductility parameter ( d ), UCS, and Hoek–Brown material constant ( m i ).…”

Section: Discussionmentioning

confidence: 99%

“…However, some rocks still exhibit brittleness even under high confining pressure at 1000 MPa or above 27 Wang and Yang 28 developed a new constitutive model based on Mohr–Coulomb (M–C) by integrating an exponential function of damage variable and confining pressure into the yield criterion to describe the brittle-ductile behavior of the crystalline rocks. Recently, Walton 29 , proposed the ductility index to reflect the brittleness of rock based on m i and (UCS) of intact rock. That is, confining stress at the brittle-ductile transition at ambient temperature under typical laboratory strain rates for a given dry, intact rock material has been proposed as a measure of brittleness and has been shown to depend directly on the (UCS) and m i .…”

Section: Introductionmentioning

confidence: 99%

Brittle-ductile transition stress of different rock types and its relationship with uniaxial compressive strength and Hoek–Brown material constant (mi)

Davarpanah

Sharghi

Narimani

et al. 2023

Sci Rep

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Rocks deformed at low confining pressure are brittle, which means that after peak stress, the strength declines to a residual value established by sliding friction. The stress drop is the variation between peak and residual values. But no tension reduction takes place at high confining pressure. A proposed definition of the brittle-ductile transition is the transition pressure at which no loss in strength takes place. However, studies that consider information about the brittle-ductile transition, the criterion's range of applicability, how to determine mi, and how confining pressures affect mi's values are scarce. This paper aims to investigate the link between brittle-ductile transition stress, uniaxial compressive strength and Hoek–Brown material constant (mi) for different kinds of rock. It is essential to accurately determine the brittle-ductile transition stress to derive reliable values for mi. To achieve this purpose, a large amount of data from the literature was chosen, regression analysis was carried out, and brittle-ductile transition stress (σTR) was determined based on the combination of Hoek–Brown failure criteria and the recently used brittle-ductile transition stress limit of Mogi. Moreover, new nonlinear correlations were established between uniaxial compressive strength and Hoek–Brown material constant (mi) for different igneous, sedimentary and metamorphic rock types. Regression analyses show that the determination coefficient between σTR and UCS for gneiss is 0.9, sandstone is 0.8, and shale is 0.74. Similarly, the determination coefficient between σTR and mi for gneiss is 0.88. The correlation between Hoek–Brown material constant (mi) and σTR was not notable for sedimentary and metamorphic rocks, probably due to sedimentary rocks' stratification and metamorphic ones' foliation.

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“…Two new brittleness indices named brittleness degree and brittleness failure intensity can work jointly to estimate the efficiency in preventing and controlling the rockburst disaster (Meng et al, 2015). The confining stress at the brittle-ductile transition of rocks is predicted by a conceptual framework to serve as an alternative brittleness index (Walton 2021). A super stiff rock mechanics testing machine was developed to capture the complete post-peak deformation for brittle hard rock that is normally failed in a Class II type (Cai et al, 2021).…”

Section: Brittleness Indices Based On Stress-strain Curvesmentioning

confidence: 99%

Evolution of rock brittleness under mechanical and thermal effects

Wang¹

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A New Perspective on the Brittle–Ductile Transition of Rocks

Cited by 25 publications

References 87 publications

Brittle Damage Processes Around Equi‐Dimensional Pores or Cavities in Rocks: Implications for the Brittle‐Ductile Transition

Brittle Damage Processes Around Equi‐Dimensional Pores or Cavities in Rocks: Implications for the Brittle‐Ductile Transition

Brittle-ductile transition stress of different rock types and its relationship with uniaxial compressive strength and Hoek–Brown material constant (mi)

Evolution of rock brittleness under mechanical and thermal effects

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