Abstract
In order to evaluate the coal pillar stability in recovery of residual room pillars under different mining rates, this paper studies the influence of loading rate on the mechanical properties of the coal body. The uniaxial compression tests of coal samples in Yangcheng area at different loading rates were carried out with the MTS815 electrohydraulic servo rock mechanics test system. The stress‐strain curves and the evolution characteristics of AE signals were analyzed. At same time, the mechanism of damage and failure of specimens are also discussed. The results show the following. (1) With the increase in loading rate, the ultimate stress and ultimate strain of specimens decrease first and then increase. (2) Loading rate has a significant effect on the stability adjustment of specimens. With the decrease in loading rate, the earlier the stress adjustment is, the larger the adjustment range is, and the failure mode changes from shear failure to tensile failure. (3) In addition, when the loading rate increases, the AE evolves from continuous dense to discrete catastrophe, which indicates that the failure of the sample at a larger loading rate is sudden, which is not conducive to the maintenance of the stability of the coal pillar. (4) Finally, the failure mechanism of the specimen structure under different loading rates is obtained, and the improvement measures for the effect of mining velocity of working face on the stability of coal pillar are put forward. The results reveal the loading rate effect of mechanical properties of coal and provide a reference for controlling the stability of the residual coal pillar.
Highlights
As a natural disaster, instability of coal pillar often poses a serious threat to safe and efficient mining, especially in room-pillar mining [1, 2]. ere are a large number of residual coal pillars left in room-pillar re-mined panels, and these pillars play an essential role in the stability of the working face [3]. erefore, it is very important to study the instability and failure mechanism of coal pillars for the safe mining of room-pillar residual coal.In room-pillar mining, the main parameters affecting the stability of coal pillars are pillar material, pillar width, pillar height, and roof strength [4, 5]
Previous studies have shown that the adjustment of load-bearing structure during loading will affect the development of microcracks and affect the strength of specimens [39, 40]
In order to explain the mechanism of the effect of loading rate on the mechanical and deformation characteristics of specimens, “Weak Structure” (WS) and “Hard Bearing Structure” (HBS) are introduced
Summary
Instability of coal pillar often poses a serious threat to safe and efficient mining, especially in room-pillar mining [1, 2]. ere are a large number of residual coal pillars left in room-pillar re-mined panels, and these pillars play an essential role in the stability of the working face [3]. erefore, it is very important to study the instability and failure mechanism of coal pillars for the safe mining of room-pillar residual coal. Erefore, it is very important to study the instability and failure mechanism of coal pillars for the safe mining of room-pillar residual coal. Zhou et al studied the influence of dynamic load on the stability of adjacent coal pillars during excavation by the numerical simulation method [13]. Erefore, the study of coal mechanical response under different loading rates will have important theoretical guidance and practical significance for ensuring the stability of pillars. E main purpose of this paper is to study the effects of loading rate on the deformation and mechanical characteristics of coal samples through experiments. According to the type of loading test machine and the mechanical state of rock, strain rate can be divided into creep, static/quasistatic, quasidynamic, dynamic, impact, and so on, as shown in Figure 1 [31,32,33]. In order to make the AE data correspond to the stress data in time, the AE data will be collected at the beginning of the experiment when the stress-strain curve appears on the loading acquisition system. e above experimental methods are sufficient to obtain the mechanical characteristics and emission distribution of samples under different loading rates
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