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Experimental investigation on acoustic emission and damage characteristics of dehydrated lignite in uniaxial compression test

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Abstract

The lignite would undergo dehydration cracking at normal temperature, which has an important impact on the stability of coal-rock slope in open-pit mine. In this paper, the uniaxial compression test of lignite with different dehydration times under normal temperature and humidity control conditions was carried out, and the mechanical parameters, deformation, AE characteristics, and macro–micro crack evolution law of dehydrated lignite were obtained. After that, the correlation between the porosity and mechanical parameters of rock samples based on dehydration deformation was discussed; meanwhile, according to the macro- and microcrack evolution characteristics of dehydrated lignite, the gradual change law of crack fractal dimension was elaborated. Finally, the initial damage of dehydrated lignite was defined by the relative porosity as a variable, and the damage constitutive model of lignite subjected to the dehydration and axial load was established. The results show the dehydration of lignite at normal temperature exactly causing the deterioration of mechanical properties, which also accompanied by the shrinkage deformation, the change of fractal dimension of macro–micro cracks, and the obvious AE activity in the compression test. In addition, the established damage constitutive model, considering the characteristics of compaction stage, is in good agreement with the experimental results. The research results are of great significance to reveal the instability and failure mechanism of lignite under the action of dehydration and stress.

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All data used in the study are included in the published article.

Abbreviations

XRD:

X-ray diffraction

XRF:

X-ray fluorescence

AE:

Acoustic emission

h:

Hour

AF:

Average frequency

\(N_{t}\) :

Porosity of lignite after \(t\) h dehydration

\(\Delta V_{tw}\) :

Water decreased volume of lignite

\(\Delta m\) :

Water decrease mass

\(\rho_{w}\) :

Density of water under 25 °C

\(V_{tr}\) :

Volume of lignite after \(t\) h dehydration

\(\Delta V_{tr}\) :

Decrease volume relative to initial state

\(A_{{{\text{dB}}}}\) :

Maximum amplitude of AE event

\(N\) :

Number of times exceeding the set threshold

\(b\) :

AE b value

\(F(s)\) :

Fractal dimension

\(N(\varepsilon )\) :

Number of boxes with \(\varepsilon\) side length in the coverage area

\(\varepsilon\) :

Side length of the box

\(D_{t}\) :

Initial damage value calculated based on relative porosity

\(\rho_{t}\) :

Relative porosity of lignite after \(t\) h dehydration

\(\rho_{\max }\) :

Maximum porosity of the dehydrated lignite

\(\sigma\), \(E\) :

Nominal stress and nominal elastic modulus, respectively

\(\sigma^{*}\), \(E^{*}\) :

Effective stress and effective elastic modulus, respectively

\(\sigma_{t}\), \(\varepsilon_{t}\) :

Stress and strain, respectively, of lignite with \(t\) h dehydration

\(E_{0}\) :

Elastic modulus without dehydration

\(E_{t}\) :

Elastic modulus of lignite with \(t\) h dehydration

\(D_{l}\) :

Damage value caused by axial load

\(D_{w}\) :

Damage variable considering the lignite dehydration and axial load

\(\eta\), \(\beta\) :

Size parameter and shape parameter, respectively

\(\sigma_{c,t}\) :

The stress at the end of compaction stage

\(\varepsilon_{c,t}\) :

The strain at the end of compaction stage

\(\sigma_{p,t}\), \(\varepsilon_{p,t}\) :

Peak stress and peak strain

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Acknowledgements

We are very grateful to the editors and reviewers for their valuable suggestions on the revising process of this paper.

Funding

We gratefully acknowledge the financial supported by the National Key Research and Development Program of China (2022YFC2904100), the State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Beijing (SKLCRSM20KFA11), and the Fundamental Research Funds for the Central Universities (2022YJSLJ09).

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Authors and Affiliations

  1. State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology (Beijing), Beijing, 100083, China

    Hongfa Ma & Yanqi Song

  2. School of Mechanics and Civil Engineering, China University of Mining and Technology (Beijing), Beijing, 100083, China

    Hongfa Ma, Yanqi Song, Jiangkun Yang, Junjie Zheng, Fuxin Shen & Zhixin Shao

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  1. Hongfa Ma
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  2. Yanqi Song
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  3. Jiangkun Yang
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  4. Junjie Zheng
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Correspondence to Yanqi Song.

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Ma, H., Song, Y., Yang, J. et al. Experimental investigation on acoustic emission and damage characteristics of dehydrated lignite in uniaxial compression test. Bull Eng Geol Environ 82, 292 (2023). https://doi.org/10.1007/s10064-023-03315-z

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  • DOI: https://doi.org/10.1007/s10064-023-03315-z

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