Scale effects and strength anisotropy in coal

Honghua Song, Yaodong Jiang, Derek Elsworth, Yixin Zhao, Jiehao Wang, Bin Liu

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

We explore microstructure-related effects of loading direction and specimen size on the anisotropy of uniaxial compressive strength in coal. We measure uniaxial compressive strength on coal samples of four different diameters (25 to 75 mm) and with varied dip of the bedding plane with respect to loading direction (0° 15° 30° 45° 60° and 90°) including characterizing the variation of microstructures in the specimens by X-ray imaging. The uniaxial compressive strength for each specimen size exhibits a unique U-shape curve against the angle of anisotropy (Jaeger, 1971). The degree of the strength anisotropy decreases with increasing specimen size, principally due to the enhanced microstructural volume of a larger specimen. The contribution of microstructures on uniaxial compressive strength differs for different orientations of loading relative to anisotropy. The rate of decline of the average uniaxial compressive strength with increasing specimen size is greatest when loading is parallel to bedding (anisotropic angle of 0°) and is the most moderate at 45°. An empirical equation relating specimen diameter with uniaxial compressive strength is proposed and verified against the experimental data. Based on this equation, the UCS of coal samples with different orientations relative to the anisotropy are predicted for the limiting sizes of zero and ∞. The anisotropy of the scale effect is also explored. Meanwhile, it is verified that a cosine relation between anisotropy angle and uniaxial compressive strength is applicable to coal specimens of different sizes. This demonstrates that the strength anisotropy in coal will remain constant when the specimen diameter is larger than a critical threshold. Based on these two observations/equations, a universal equation relying on the minimum strength angle, friction angle and Weibull coefficients is proposed and verified against experimental data to describe the relationship among anisotropy angle, specimen size, and uniaxial compressive strength in coal.

Original languageEnglish (US)
Pages (from-to)37-46
Number of pages10
JournalInternational Journal of Coal Geology
Volume195
DOIs
StatePublished - Jul 1 2018

Fingerprint

scale effect
compressive strength
Compressive strength
Anisotropy
anisotropy
Coal
coal
microstructure
Microstructure
bedding plane
dip
friction
Friction
Imaging techniques
X rays

All Science Journal Classification (ASJC) codes

  • Fuel Technology
  • Geology
  • Economic Geology
  • Stratigraphy

Cite this

Song, Honghua ; Jiang, Yaodong ; Elsworth, Derek ; Zhao, Yixin ; Wang, Jiehao ; Liu, Bin. / Scale effects and strength anisotropy in coal. In: International Journal of Coal Geology. 2018 ; Vol. 195. pp. 37-46.
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Scale effects and strength anisotropy in coal. / Song, Honghua; Jiang, Yaodong; Elsworth, Derek; Zhao, Yixin; Wang, Jiehao; Liu, Bin.

In: International Journal of Coal Geology, Vol. 195, 01.07.2018, p. 37-46.

Research output: Contribution to journalArticle

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