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Mechanical Properties and Failure Behavior of Dry and Water-Saturated Anisotropic Coal Under True-Triaxial Loading Conditions

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Abstract

In underground coal mining, coal failure generally occurs due to the relatively weak strength of the coal and the high applied mining-induced stresses. The outer complex geological conditions (i.e., tectonic structure and water intrusion) and internal structural anisotropy of the coal introduce uncertainty in predicting its mechanical properties and failure behavior. In this study, laboratory investigations of the mechanical properties and failure behavior of dry and water-saturated anisotropic coal samples subjected to different true-triaxial loading stresses were conducted. The effects of water weakening, intermediate stress, and structural anisotropy on the mechanical properties and failure behavior of the coal were systematically studied. The results indicate that the presence of water significantly reduced the strength, elastic modulus, and strength anisotropy of the coal. The maximum stress at failure first increased and then decreased with increasing intermediate stress. The residual strength-to-peak strength ratios and failure plane angles of the coal showed a linear increase with increasing intermediate stress. When the coal samples were loaded in the bedding plane direction, the brittleness of the coal was higher than when they were loaded in the other two cleat plane directions. In addition, when the coal samples were loaded in the butt cleat plane direction, the brittleness of the coal decreased with increasing intermediate stress. Two typical failure modes of the dry and water-saturated coal samples were observed: shear and mixed splitting and shear failures. The dominant failure mode of the coal also varied with the loading direction relative to the weakness planes, which could be well recognized and predicted by the acoustic emission (AE) characteristic curves. To further reveal the fracture mechanism, the microcrack patterns of the coal were further identified based on the AE parameters.

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Abbreviations

σ 1 :

The maximum stress

σ 2 :

The intermediate stress

σ 3 :

The minimum stress

E :

Elastic modulus

M :

Postpeak modulus

v :

Poisson’s ratio

x :

The distance into the coal pillar

h :

The coal pillar height

B1, B2 :

The brittleness index

W r :

The postpeak rupture energy

W e :

The elastic energy

W a :

The released energy

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Acknowledgements

This study was financially supported by the National Natural Science Foundation of China (51804049, 51674049) and the Graduate Research and Innovation Foundation of Chongqing (CYB18033). The first author also acknowledges the financial support provided by the Chinese Scholarship Council (CSC).

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Authors and Affiliations

  1. State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing, 400030, China

    Yubing Liu, Guangzhi Yin, Minghui Li, Dongming Zhang, Gun Huang, Peng Liu, Chao Liu, Honggang Zhao & Beichen Yu

  2. School of Resources and Safety Engineering, Chongqing University, Chongqing, 400030, China

    Yubing Liu, Guangzhi Yin, Minghui Li, Dongming Zhang, Gun Huang, Peng Liu, Chao Liu, Honggang Zhao & Beichen Yu

  3. Department of Exploration Geophysics, Curtin University, 26 Dick Perry Avenue, Kensington, 6151, Australia

    Yubing Liu

  4. Guangdong Provincial Key Laboratory of Deep Earth Sciences and Geothermal Energy Exploitation and Utilization, Institute of Deep Earth Sciences and Green Energy, College of Civil and Transportation Engineering, Shenzhen University, Shenzhen, 518060, China

    Minghui Li

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  1. Yubing Liu
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  2. Guangzhi Yin
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Liu, Y., Yin, G., Li, M. et al. Mechanical Properties and Failure Behavior of Dry and Water-Saturated Anisotropic Coal Under True-Triaxial Loading Conditions. Rock Mech Rock Eng 53, 4799–4818 (2020). https://doi.org/10.1007/s00603-019-02035-9

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