The effect of pre-existing microcavities on mechanical rock performance in sedimentary and crystalline rocks

Howarth, D.F.

doi:10.1016/0148-9062(87)90177-x

Cited by 32 publications

(9 citation statements)

References 12 publications

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“…Many experimental studies have demonstrated that the microcracks induced during loading of granitic rocks are predominantly tensile cracks oriented perpendicular to the maximum tensile stress axis or parallel to the maximum compressive stress axis (e.g. Hadley 1976;Tapponier & Brace 1976;Kranz 1979;Wong 1982;Howarth 1987;Holcomb 1993). Direct observations of the microcrack orientation in the laboratory samples (Batzle, Simmons & Siegfried 1980Reches & Lockner 1994Moore & Lockner 1995) also give a narrow orientation distribution ( Fig.…”

Section: Approachmentioning

confidence: 99%

Non-linear elastic behaviour of damaged rocks

Lyakhovsky

Reches

Weinberger

et al. 1997

Geophysical Journal International

111

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S U M M A R YThe pervasive damage of rocks by microcracks and voids stron ly affects their macroscopic elastic properties. To evaluate the damage effects, w d derive here the macroscopic stress-strain relations for a 3-D elastic solid with nohinteracting cracks embedded inside a homogeneous matrix. The cracks considered are oriented either perpendicular to the maximum tension axis, or perpendicular to the maximum compression axis. In the first case they dilate during loading and in the second case they contract during loading. We derive a solution for the elastic energy of this rock following the self-consistent scheme of Budiansky & O'Connell ( 1976). The solution describes the stress-strain relations in terms of Ad and pd, which are the modified Lame constants, and an additional parameter y. The latter accounts for the non-linear behaviour of the solid and is related to crack density. The solution predicts a non-linear elastic rheology even for an infinitesimal strain of ~<0.001, and abrupt change in the elastic moduli when the loading reverses from uniaxial compression to uniaxial tension.We use the derived solution to analyse rock-mechanics experiments in which beams of Indiana limestone were deformed under four-point loading. This configuration provides simultaneously the apparent tensile and compressive moduli for small strains. The apparent moduli fit the effective elastic moduli calculated with the present damage model well, including the differences between tensile and compressive moduli.

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Section: Approachmentioning

confidence: 99%

Non-linear elastic behaviour of damaged rocks

Lyakhovsky

Reches

Weinberger

et al. 1997

Geophysical Journal International

111

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“…Morley (1944) and Hetenyi (1966) define brittleness as the lack of ductility. Ramsey (1967) defined brittleness as follows: ''When the internal cohesion of rocks is broken, the rocks are said to be brittle''.…”

Section: Brittlenessmentioning

confidence: 99%

“…Nevertheless, there is no agreement between different authors whether as to definition, or as to measure brittleness. Different researchers mean, express and use it differently (Coates 1966;Hetenyi 1966;Ramsey 1967;Obert and Duvall 1967;Reichmuth 1967;Hucka and Das 1974;McFeat-Smith 1977;Singh 1986;Goktan 1991Goktan , 1992Inyang and Pitt 1990;Inyang 1991;George 1995;Altindag 1997Altindag , 2000Altindag , 2002Copur 1999;Kahraman 2002).…”

Section: Brittlenessmentioning

confidence: 99%

Prediction of TBM penetration rate from brittleness indexes using multiple regression analysis

Jamshidi

2018

Model. Earth Syst. Environ.

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One of the most important aspects in the excavation of tunnels with a Tunnel Boring Machine (TBM) is the reliable prediction of its penetration rate. This affects the planning and other decision making on the organization of the construction site of the tunneling project, and, therefore, total costs. In this study, raw data obtained from the experimental works of different researchers were used to establish the new statistical models for prediction of rock TBM penetration rate from brittleness indexes, B 1 , B 2 , and B 3 . For this, correlation between the TBM penetration rate with brittleness indexes statistically was investigated using multiple regression analyses. In these analyses, the TBM penetration rate was considered to be the dependent variable, which is dependent on the independent variables of the brittleness indexes. The validity of the predictive models was validated by statistical tests. The results showed that statistical models are in good accuracy for prediction of TBM penetration rate, and thus making a rapid assessment of the TBM performance.

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“…The process zone migrated across the cylinder along with the propagating fracture. Previous studies (e.g., Hadley, 1976;Tapponnier and Brace, 1976;Kranz, 1979;Wong, 1982;Howarth, 1987) have shown that the stress-induced cracks generated prior to sample failure are principally tensile cracks that have a roughly axial orientation (Figure 2a). if the microcracks generated in the process zone are also predominantly tensile cracks, their orientations should reflect the stress fields associated with the shear fracture, as illustrated in Figure 2b.…”

Section: Introductionmentioning

confidence: 99%

Microcrack populations associated with a propagating shear fracture in granite

Moore¹

1993

Open-File Report

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Maps and summary tables are presented of microcracks generated during a brittle faulting experiment on Westerly granite. Granite located well away from the shear fracture in the stressed sample contains twice the crack density of the undeformed granite, and the stressinduced microcracks of the far-field area have a roughly axial orientation consistent with tensile cracks formed in response to loading. Microcrack densities increase markedly in the process zone in front of the fracture tip, and at the tip the densities are over an order of magnitude higher than in the undeformed rock. Microcracks generated within the process zone are predominantly tensile cracks that reflect the stress fields associated with the shear fracture, but some cracks form in response to the physical requirements of extending the fracture. The orientations found for the total crack populations also hold for the grain-boundary and intragranular cracks considered separately. The largest number of cracks and the smallest average crack length were found in the process zone immediately in front of the fracture tip.Grain-boundary cracks comprise about half the microcrack population of the undeformed granite but only a small proportion of the highly cracked areas in the process zone and adjacent to the shear fracture. The grain-boundary cracks are nevertheless significant in the stressed sample in providing a connected network of cracks. Microcracking in the undeformed granite sample is highly concentrated within and along the boundaries of quartz. Near the shear fracture, intragranular cracks are slightly concentrated in K-feldspar but grain-boundary cracks remain most closely associated with quartz. Comparison of the crack and mineral maps reveals marked crystal-to-crystal variations in crack density that are caused by varying crystallographic orientations relative to the imposed stress fields.

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The effect of pre-existing microcavities on mechanical rock performance in sedimentary and crystalline rocks

Cited by 32 publications

References 12 publications

Non-linear elastic behaviour of damaged rocks

Non-linear elastic behaviour of damaged rocks

Prediction of TBM penetration rate from brittleness indexes using multiple regression analysis

Microcrack populations associated with a propagating shear fracture in granite

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