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Fractal and volume characteristics of 3D mining-induced fractures under typical mining layouts

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Abstract

Mining-induced fractures, which can release natural gas and enhance gas migration, are indispensable in the co-extraction of coal and methane (CECM). Investigations into mining-induced fracture systems ahead of the coalface are beneficial in elucidating the complex differences between mining processes and their related static and dynamic strata stress fields. Triaxial tests were conducted on coal samples to simulate the mining-induced mechanical behaviors of the coal seam under three widely used mining processes, i.e., top-coal caving mining (TCCM), non-pillar mining (NPM) and protected coal seam mining (PCSM). Mining-induced fractures were created at the laboratory scale. An industrial computed tomography scanning system was employed to scan the ruptured coal samples and measure the geometric characteristics of the fractures associated with each simulated process. Coronal and sagittal views as well as a precise 3D solid geometrical model were reconstructed for each process. It is shown that the mining layout influences the spatial morphology of mining-induced fractures. Using the box-counting method, a quantitative fractal characterization of the fracture system was estimated for each mining method. The estimated average fractal dimensions of the fracture systems generated in the simulated TCCM, NPM, and PCSM processes were 2.0557, 2.0362 and 2.0129, respectively. Additionally, a scale-independent fracture intensity, FI, was defined to further characterize the volume features of the mining-induced fracture systems. The fracture intensity was 0.6 for the NPM process, 0.5 for TCCM and 0.21 for PCSM.

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Abbreviations

CECM:

Co-extraction of coal and methane

CBM:

Coal bed methane

TCCM:

Top-coal caving mining

NPM:

Non-pillar mining

PCSM:

Protected coal seam mining

CT:

Computed tomography

μ-XCT:

X-ray microfocus computed microtomography

FEA:

Finite element analysis

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Acknowledgments

The authors would like to express their sincere gratitude to all of the anonymous reviewers for their suggestions and comments for improving the quality of our paper. This work was financially supported by the Major State Fundamental Research Project of China (Nos. 2011CB201201), the National Natural Science Foundation of China (No. 51204113, 51134018) and the Youth Science and Technology Fund of Sichuan Province (No. 2012JQ0031).

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Authors and Affiliations

  1. State Key Laboratory of Hydraulics and Mountain River Engineering, College of Hydraulic and Hydropower Engineering, Sichuan University, Chengdu, 610065, China

    R. Zhang & Z. T. Zhang

  2. School of Architecture and Environment, Sichuan University, Chengdu, 610065, China

    T. Ai

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

    H. W. Zhou & Y. Ju

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  1. R. Zhang
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  2. T. Ai
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  3. H. W. Zhou
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  4. Y. Ju
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  5. Z. T. Zhang
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Correspondence to T. Ai.

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Zhang, R., Ai, T., Zhou, H.W. et al. Fractal and volume characteristics of 3D mining-induced fractures under typical mining layouts. Environ Earth Sci 73, 6069–6080 (2015). https://doi.org/10.1007/s12665-015-4376-9

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  • DOI: https://doi.org/10.1007/s12665-015-4376-9

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