Experimental Investigation of the Creep Behaviour of Coal by Monitoring Changes of Acoustic Properties

Time-dependent deformation of coal is a major concern for deep coal mining. When experiencing high stress conditions, the enhanced time-dependent deformation of coal will become a very possible factor to trigger the violent failure of underground openings. For this study, the inner structural variat...

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Bibliographic Details
Published in:Applied sciences 2018-04, Vol.8 (4), p.633
Main Authors: Yang, Sen, Zhang, Nong, Feng, Xiaowei, Kan, Jiaguang
Format: Article
Language:English
Subjects:
acoustic attenuation
Acoustic properties
Acoustics
Coal
coal creep
Coal mining
Coal-fired power plants
Concrete
Creep tests
Global economy
Inhomogeneity
Laboratories
long-term ground stability
Mathematical models
Microcracks
Mines
S waves
Stone
wave velocity
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Summary:Time-dependent deformation of coal is a major concern for deep coal mining. When experiencing high stress conditions, the enhanced time-dependent deformation of coal will become a very possible factor to trigger the violent failure of underground openings. For this study, the inner structural variation of an extremely inhomogeneous coal subjected to incremental creep stress has been experimentally investigated by monitoring both the macroscopic deformation and acoustic property. Results show the following: (1) The pronounced inhomogeneity of coal induces considerable irregularities in creep strain data collected during the increase of stress level. These flawed data highlight the shortcomings of conventional strain-time relationship experiments for deciphering the mechanisms that control creep; (2) The mechanical response of samples under creep compression is the result of competition between compaction and cracking. Cracking deteriorates the structure and increases the ultrasonic attenuation, whilst the compaction causes the densification along the axial axis and reduces attenuation; (3) Long-term creep involves multiple structural deformations that alter the internal structure of the coal. This results in fluctuations of the ultrasonic velocities and their dynamic moduli; (4) During uploading phase of short term creep, vertical cracks develop and transform the sample into a structure consisting of separated columns. Further deterioration of the coal increases the possibility of tensile and shear failure of individual columns, which can trigger the violent collapse of an already fragile structure.
ISSN:2076-3417
2076-3417
DOI:10.3390/app8040633