Abstract
Briquette coals with different cement contents are frequently used to study the coal body’s properties. In this study, the deformation and strength of briquette coal samples with 0, 5, 10, and 20% cement contents were experimentally and theoretically investigated using the acoustic emission (AE) characteristics monitored during the uniaxial compression tests. The results show that the uniaxial compression process of raw coal and briquette coal samples can be subdivided into compaction, elastic, plastic (yield), and brittle failure stages. With an increase in cement content, briquette coal samples undergo the elastic and plastic stages, and their postpeak stress drop rate gradually grows, and their plastic deformation is followed by brittle failure. The uniaxial compressive strength and elastic modulus of briquette coal samples show a linearly increasing relationship with cement content, while their Poisson’s ratio decreases gradually. During the uniaxial compression, raw coal and briquette coal samples produce the AE signals. The overall AE signal of briquette coal samples is relatively low, and there are no obvious AE events in raw coal samples. The uniaxial compressive strength, elastic modulus, and Poisson’s ratio of briquette coal samples with a 20% cement content and their AE signal cumulative amplitude, count, and energy values are very close to the corresponding parameters of raw coal samples. Therefore, they can be used for simulating raw coal samples in laboratory tests.
Highlights
Coal production is jeopardized by coal and gas outbursts, with a large amount of gas and coal and rock mass sprayed out from the outburst mouth, which often results in serious casualties and huge economic losses [1, 2]
During the mechanical loading of coal samples, a DS-5 type 8-channel acoustic emission (AE) system was used for the online AE monitoring. e AE sensor was installed in the middle of the coal sample and fixed with the insulating tape. e sampling frequency was set to 3 MHz, the RS-2A AE sensor frequency was 150 kHz with the threshold value for mechanical and ambient noise was set 50 dB. e data acquisition system recorded a series of parameters, such as AE amplitude, count, and energy on a real-time scale
Deformation, strength, and AE characteristics of raw coal and briquette coal samples with different cement contents obtained during the uniaxial compression tests were analyzed and discussed in detail. e main conclusions are as follows: (1) e process of uniaxial compression of raw coal and briquette coal samples with different cement contents can be subdivided into compaction, elastic, plastic, and failure stages
Summary
Coal production is jeopardized by coal and gas outbursts, with a large amount of gas and coal and rock mass sprayed out from the outburst mouth, which often results in serious casualties and huge economic losses [1, 2]. E mechanical properties and AE characteristics of coal and rock bodies have been studied by numerous researchers. Wang et al [13] studied the characteristics of the AE spectrum generated during the fracture of raw coal samples under uniaxial compression. Yang et al [14] investigated the AE characteristics of raw coal samples under uniaxial compression and concluded that the fracture of coal rock masses could be predicted by the AE monitoring results. Su et al [17] conducted uniaxial compression tests on raw coal samples of two scales with the AE monitoring and concluded that it is more reasonable to predict the coal and rock dynamic disasters using the AE characteristic values of large raw coal samples. In the research of adding cement to briquette, Jasinge et al [21, 22] found that the closest match for the natural coal samples were reconstituted coal samples with a 4% cement content and 50% water content
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