## 4 Discussion  
### Acoustic Emission Characteristics  
Figure 8 displays the acoustic emission curves for coal rock ringing and the cumulative ringing of the coal rock specimen corresponding to the stress-strain curve. The cumulative acoustic emission ringing curves for the specimen exhibit a stage with an increase in strain. During the compacting stage (stage I), the specimen's acoustic emission activity decreases, as internal pores and cracks gradually become compacted. Furthermore, new microcracks are not generated, and almost no energy is released. In the linear elasticity stage (stage II), the specimen's acoustic emission activity increases, but not to a significant extent. The ringing counts and cumulative ringing counts only increase slightly, while the microcracks inside the specimen expand steadily. During the yielding stage (stages II-III), the acoustic emission of the specimen becomes active, causing a significant increase in signal and permanent damage cracks. The expansion of unstable cracks on the surface is accompanied by the detachment of the coal rock, leading to an increase in internal loose particles. Accordingly, the compression and densification of the particles result in increased strength until peak stress, where the specimen's strength undergoes a zigzag-type reduction. At this stage, the specimen's acoustic emission ringing count sharply increases, and the cumulative ringing count continues to rise, suggesting the ongoing release of a significant amount of acoustic emission and strain energy. During the post-peak strain softening stage (stage IV), there is a decrease in the specimen's acoustic emission activity. Additionally, there is a reduction in the degree of growth of the cumulative ringing number, which eventually reaches a maximum value of 1.05 \(\times\) 10\({}^{5}\) before disappearing as the loading process comes to a halt. The ringing characteristics and cumulative ringing numbers of the immersed specimens are presented in Figure 9. The acoustic emission strain-ringing cumulative number curves of the specimens undergoing varying immersion durations exhibit comparable patterns to those of the unimmersed specimens, and the specimens can be categorized into  
Figure 8: Characteristics of energy and accumulated AE counts of natural coal samples at stage I–IV (0 d). four phases based on the uniaxial compression process. Upon initial analysis, the results appear congruent with the anticipated outcomes. During the compression-density phase, the specimens are in a compressed and dense state, resulting in decreased acoustic emission activity characterized by mainly small-energy events and a slow increase in cumulative ringing. In the linear elasticity stage, the specimen's acoustic emission activity is similarly low, with a maximum number of rings of less than 100, and the specimen remains undamaged. During the pre-peak stage of fissure stability development, the specimen exhibits active acoustic emission events. The degree of activity varies depending on the immersion length. Specifically, the immersion lengths of 1 d, 3 d, 5 d, and 7 d register maximum ringing numbers of 478, 729, 513, and 274, respectively. The cumulative increase in the ringing number is significant and corresponds to the internal damage of the specimen at this stage. Additionally, the number of broken particles increases. During the stage of crack instability development, the specimen reaches its peak stress attachment. At this point, acoustic emission events rapidly grow and are often accompanied by sudden increases in energy, particularly near the peak stress. This suggests that a substantial amount of strain energy is released during damage. Additionally, the cumulative number of rings experiences significant growth, plateauing after unloading. Finally, cracks appear on the specimen's surface, leading to plastic damage. The process of acoustic emission energy change in the water-immersed specimen corresponds with the stress-strain curve.