In situ strength of coal bed based on the size effect study on the uniaxial compressive strength

Gonzatti, Clovis; Zorzi, Luiz; Agostini, Ivone Maria; Fiorentini, João Alberto; Viero, Antonio Pedro; Philipp, Ruy Paulo

doi:10.1016/j.ijmst.2014.10.003

Cited by 31 publications

(10 citation statements)

References 4 publications

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“…At 103. 45 MPa, the thickness of >99.99% micro-cracks ranges from 10.75-127.66 µm, and the thickness of 49.93% cracks is within a range from 60-80 µm. The increase of the 60-80 µm thick micro-cracks may be caused by the development of new micro-cracks and/or the enlargement of the smaller micro-cracks that developed during the previous stage.…”

Section: ° Orientationmentioning

confidence: 98%

“…Although the size effect on mechanical properties, especially for rock, is very complicated, it has been revealed that UCS reduces with an increase in specimen size, following the exponential decay laws on the basis of majority tests on coal specimens with increasing diameter [43][44][45][46][47]. The elastic modulus of coal specimens decreased with an increase of diameter by means of a negative power function, nearly independent of the confining pressure.…”

Section: Mechanical Property Measurementsmentioning

confidence: 99%

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Mechanical Property Measurements and Fracture Propagation Analysis of Longmaxi Shale by Micro-CT Uniaxial Compression

et al. 2018

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The mechanical properties and fracture propagation of Longmaxi shale loading under uniaxial compression were measured using eight cylindrical shale specimens (4 mm in diameter and 8 mm in height), with the bedding plane oriented at 0 • and 90 • to the axial loading direction, respectively, by micro computed tomography (micro-CT). Based on the reconstructed three-dimensional (3-D) CT images of cracks, different stages of the crack growth process in the 0 • and 90 • orientation specimen were revealed. The initial crack generally occurred at relatively smaller loading force in the 0 • bedding direction specimen, mainly in the form of tensile splitting along weak bedding planes. Shear sliding fractures were dominant in the specimens oriented at 90 • , with a small number of parallel cracks occurring on the bedding plane. The average thickness and volume of cracks in the 90 • specimen is higher than those for the specimen oriented at 0 • . The geometrical characterization of fractures segmented from CT scan binary images shows that a specific surface area correlates with tortuosity at the different load stages of each specimen. The 3-D box-counting dimension (BCD) calculations can accurately reflect crack evolution law in the shale. The results indicate that the cracks have a more complex pattern and rough surface at an orientation of 90 • , due to crossed secondary cracks and shear failure.Various experimental methods, e.g., electromagnetic radiation (EMR), acoustic emission (AE), micro-seismic (MS), infrared technique, high speed digital imaging, and computerized tomography (CT), have been used to analyze the mechanical behavior of rocks (including shale) during uniaxial or triaxial loading [15][16][17][18][19][20][21]. CT scanning has been widely applied in the investigation of damage propagation since 1997, due to the three-dimensional (3-D) visualization and high-resolution imaging [22][23][24][25][26][27][28]. Kawakata et al. used CT to study the initial mesoscopic damage characteristics of rock materials, and observed spatial fault development in granite undergoing compression [29,30]. In the experiment, only the damaged specimens, rather than the entire process from crack initiation to specimen destruction, were scanned, and then observed by 3-D reconstruction of X-ray CT images. To examine the entire process, Ge et al. investigated rock compression with a real-time CT test [23]. Through the use of the industrial CT images, the rock meso-damage propagation law was revealed. Rock failure started with micro-pore and micro-crack compression, growth, bifurcation, and development, followed by fracture. Sun et al. displayed real-time deformation in backfill body under loading using industrial CT in several slices, and provided insights into the process of faulting [31]. However, the relatively low spatial resolution and image quality of conventional industrial CT is not suitable for fine-grained rocks. Furthermore, the 3-D information was not fully captured or used, which limited the accuracy of further calculation ...

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Section: ° Orientationmentioning

confidence: 98%

Section: Mechanical Property Measurementsmentioning

confidence: 99%

Mechanical Property Measurements and Fracture Propagation Analysis of Longmaxi Shale by Micro-CT Uniaxial Compression

et al. 2018

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“…Coal industry serves an important role in the rapid growth of China's economy, and the increase in coal demand has brought an increase in the depth of mining. As a result, many disasters have occurred, causing a large number of casualties and property losses . Figure shows a statistical chart of the causes for different coal mine accidents (eg, blasting, gas, fire, floor, transportation, electromechanical, and other disasters) in China from 2007 to 2017.…”

Section: Introductionmentioning

confidence: 99%

Theoretical, numerical, and experimental analysis of effective extraction radius of coalbed methane boreholes by a gas seepage model based on defined criteria

Wang

Chang

et al. 2019

Energy Science & Engineering

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The effective extraction radius of borehole is the main parameter for determining the design and layout for coalbed methane extraction. This paper is aimed at the problem that the criteria and calculation methods for the effective extraction radius of coal seams are not comprehensive. With Wudong Coal Mine in China taken as an example, the critical gas pressure (0.441 MPa) for the calculation of effective extraction radius is first defined. Next, the gas seepage unit model around the borehole is developed, and the theoretical mathematical expression to calculate the effective extraction radius is derived. Then, the numerical simulation of gas extraction is carried out through a computational fluid dynamics program, and the effective extraction radius is obtained numerically. Furthermore, the influence of original gas pressure, borehole diameter, and negative pressure of gas extraction on gas extraction is analyzed. Finally, the results from the theoretical calculation and numerical simulation are validated by the field engineering measurement and the average relative error is small (less than 10%). The results indicate that the effective extraction radius has a linear relationship with the extraction time. Moreover, it is found that the original gas pressure is the main factor affecting the effective extraction radius and the effective extraction radius is proportional to the borehole diameter and negative pressure through analysis. Therefore, the above findings can provide a theoretical basis for determining parameters such as borehole spacing and extraction time of gas extraction in coal mines.

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“…As natural features, both anisotropy and scale effect are also found to be present in AE in coal/rock as the loading direction and the specimen scale change [15][16][17][18]. In general, investigating the scale effect on the mechanical properties of coal and rock is beneficial for the upscaling of the laboratory experimental results to the field use [19][20][21]. Studying the anisotropic AE features in coal/rock is helpful in preventing the various dynamic disasters (coal bump, rock burst, and coal and gas outbursts) and mining failures.…”

Section: Introductionmentioning

confidence: 99%

Scale Effect on the Anisotropy of Acoustic Emission in Coal

Song

Zhao

Jiang

et al. 2018

Shock and Vibration

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Acoustic emission (AE) in coal is anisotropic. In this paper, we investigate the microstructure-related scale effect on the anisotropic AE feature in coal at unconfined loading process. A series of coal specimens were processed with diameters of 25 mm, 38 mm, 50 mm, and 75 mm (height to diameter ratio of 2) and anisotropic angles of 0°, 15°, 30°, 45°, 60°, and 90°. The cumulative AE counts and energy dissipation increase with the specimen size, while the energy dissipation per AE count behaves in the opposite way. This may result from the increasing amount of both preexisting discontinuities and cracks (volume/number) needed for specimen failure and the lower energy dissipation AE counts generated by them. The effect of microstructures on the anisotropies of AE weakens with the increasing specimen size. The TRFD and its anisotropy reduce as the specimen size increases, and the reduction of fractal dimension is most pronounced at the anisotropic angle of 45°. The correlation between TRFD and cumulative AE energy in the specimens with different sizes are separately consistent with the negative exponential equation proposed by Xie and Pariseau. With the specimen size gain, the reduction of the TRFD weakens with the increasing amount of cumulative absolute AE energy.

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In situ strength of coal bed based on the size effect study on the uniaxial compressive strength

Cited by 31 publications

References 4 publications

Mechanical Property Measurements and Fracture Propagation Analysis of Longmaxi Shale by Micro-CT Uniaxial Compression

Mechanical Property Measurements and Fracture Propagation Analysis of Longmaxi Shale by Micro-CT Uniaxial Compression

Theoretical, numerical, and experimental analysis of effective extraction radius of coalbed methane boreholes by a gas seepage model based on defined criteria

Scale Effect on the Anisotropy of Acoustic Emission in Coal

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