Experimental Studies on Anisotropy of Time-Dependent Behaviour of Bedded Rocks

Kwaśniewski, Marek; Nguyen, H.V.

doi:10.1016/b978-0-08-035894-9.50047-0

Cited by 7 publications

(5 citation statements)

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“…The results showed that when the creep stress was greater than 22% of σ c , the steady creep rate showed an inverted U-shaped or shoulder shaped anisotropy. The maximum creep rate occurred at α = 35° and 45°, and the minimum creep rate was observed at α = 0° and 90°, which differed from the results obtained by Kwasniewski and Nguyen (1988), as shown in Fig. 2…”

Section: Introductioncontrasting

confidence: 82%

“…Triaxial creep tests of Callovo-Oxfordian argillite showed that when the creep stress σ cr was 82% of its failure stress σ c , the steady creep rate of the specimen with horizontal bedding planes (α = 0°) was slightly greater than that of the specimen with vertical bedding planes (α = 90°) (Liu et al 2015). Kwasniewski and Nguyen (1988) conducted a series of uniaxial creep tests on three types of shales with different bedding angle orientations. The results showed that when the creep stress was 70% of σ c , the steady creep rate exhibited a decreasing order-shaped anisotropy, as shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

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Effect of structural anisotropy on compressive creep behavior of composite rock based on digital image correlation

Tian

Shu

Chen

et al. 2022

Preprint

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In this study, a series of uniaxial creep tests were conducted on three-dimensional printed (3DP) composite rock specimens to investigate the effects of structural anisotropy on the time-dependent behavior of the rock. Digital image correlation (DIC) was used to monitor the evolution of the full-field strain during creep tests. The Burgers model was used to analyze the anisotropic creep behavior of the composite rock. When the specimen was subjected to a low creep stress (σcr ≤ 0.55σc (failure stress of the specimen)), the creep strain was mainly induced by transient creep, and the transient creep parameter Ek exhibited increasing order-shaped anisotropy. When the specimen was subjected to a high creep stress (σcr ≥ 0.70 σc), the creep strain of the specimen was dependent on steady creep, and the steady creep parameter ηm showed U-shaped anisotropy similar to the compression strength anisotropy of the specimen. DIC observations showed that the strain concentration along the soft layer was an important factor that resulted in anisotropic creep, and the time-dependent shearing slip between the soft layer and hard material enhanced the creep anisotropy under a high creep stress. The failure modes of the specimens showed that creep failure developed first in the soft layer, and the creep process had an insignificant influence on the failure modes of the composite rock.

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Section: Introductioncontrasting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Effect of structural anisotropy on compressive creep behavior of composite rock based on digital image correlation

Tian

Shu

Chen

et al. 2022

Preprint

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“…Data of E from 16 rocks are collected which can be classified into six rock types: schist , shale , gneiss , coal , diatomite , and sandstone . In Table , the first column lists the Young's modulus when β = 0°, the second column lists the minimum modulus, and the third column lists the Young's modulus when β = 90°.…”

Section: Overview Of Experimental Resultsmentioning

confidence: 99%

Discrete element method modeling of inherently anisotropic rocks under uniaxial compression loading

Kang

Kwok

Pierce

2015

Num Anal Meth Geomechanics

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SUMMARYA new numerical approach is proposed in this study to model the mechanical behaviors of inherently anisotropic rocks in which the rock matrix is represented as bonded particle model, and the intrinsic anisotropy is imposed by replacing any parallel bonds dipping within a certain angle range with smooth-joint contacts. A series of numerical models with β = 0°, 15°, 30°, 45°, 60°, 75°, and 90°are constructed and tested (β is defined as the angle between the normal of weak layers and the maximum principal stress direction). The effect of smooth-joint parameters on the uniaxial compression strength and Young's modulus is investigated systematically. The simulation results reveal that the normal strength of smooth-joint mainly affects the behaviors at high anisotropy angles (β > 45°), while the shear strength plays an important role at medium anisotropy angles (30°-75°). The normal stiffness controls the mechanical behaviors at low anisotropy angles. The angle range of parallel bonds being replaced plays an important role on defining the degree of anisotropy.Step-by-step procedures for the calibration of micro parameters are recommended. The numerical model is calibrated to reproduce the behaviors of different anisotropic rocks. Detailed analyses are conducted to investigate the brittle failure process by looking at stress-strain behaviors, increment of micro cracks, initiation and propagation of fractures. Most of these responses agree well with previous experimental findings and can provide new insights into the micro mechanisms related to the anisotropic deformation and failure behaviors. The numerical approach is then applied to simulate the stress-induced borehole breakouts in anisotropic rock formations at reduced scale. The effect of rock anisotropy and stress anisotropy can be captured.

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“…Based on this model, the authors further simplified the layered rock mass as a layered composition of plate-like uniform elastomers, and the mechanical properties of each layer of material correspond to different elastic parameters. Many researchers carried out uniaxial compressive tests and Brazilian splitting tests of plate-like rocks (shale, schist, mudstone) and summarized the change law of compressive strength, tensile strength, elastic modulus, and Poisson's ratio [9][10][11][12]. Pomeroy et al [13] conducted triaxial compression tests on hard coal rock and diatomite rock, respectively, then analyzed the changes of mechanical parameters with the increase of confining pressure.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study on the Effect of Bedding on the Fracture Process Zone of Shale

et al. 2022

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The conventional fracture in shale hydraulic fracturing belongs to the type-I fracture, and the size of the fracture process zone (FPZ) is an important index to measure the fracability of rock mass. This index is also one of the feasible entry points to study the complexity of the fracture network. In order to visually observe the type-I FPZ at the tip of shale fractures, and to study the relationship between the mechanical properties, the shape and size of the FPZ, and the bedding structure, Notched Semi-Circular Bend (NSCB) tests were conducted with three typical fracture direction-bedding orientations (splitter, arrester, divider). The digital image correlation (DIC) method was used to realize the intuitive observation of the real fracture process and the FPZ near the fracture tip. The test found that the FPZ of shale is narrow and long as a whole and is “flame-like”. The height-to-length ratio of the FPZ at the fracture tip determines whether bending and deflection happen between the new fracture and the prefabricated cracks when the fracture occurs. Most of the specimens often appear in the FPZ with a beaded high shear strain zone before the fracture, which is caused by the oblique communication of micro-cracks in the FPZ before the fracture. The appearance of a beaded zone of high shear strain indicates that macroscopic fracture is imminent. The research results can be used for the design of disaster early warning and prevention programs.

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Experimental Studies on Anisotropy of Time-Dependent Behaviour of Bedded Rocks

Cited by 7 publications

References 1 publication

Effect of structural anisotropy on compressive creep behavior of composite rock based on digital image correlation

Effect of structural anisotropy on compressive creep behavior of composite rock based on digital image correlation

Discrete element method modeling of inherently anisotropic rocks under uniaxial compression loading

Experimental Study on the Effect of Bedding on the Fracture Process Zone of Shale

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