## 5 Discussion and Conclusions  
The free surface is intact and smooth before the rockburst. The phenomenon of small particles rock ejecting occurred to the free surface in the process of a slight rockburst. During the violent rockburst, the rock block was fiercely ejected from the free surface, accompanied by spray rock powders, and an explosion sound can be heard. After the destruction of the rockburst, the specimen's surface left multiple split cracks and penetrating sheared cracks. The free surface became a rockburst destruction surface and a typical rockburst pit was shaped as a V type in the ejection area. However, the surface with additional binding force remained intact and smooth.  
The effective acoustic emission signals of the whole test process were decomposed and reconstructed by five-layer wavelet processing. The energy distribution coefficients of each frequency band were concentrated in the compaction and destruction phases. The energy distribution coefficient's tendency in the frequency band of 125-250 kHz shows a valley-type in the destruction stage. The energy distribution coefficients of the frequency band of 125-250 kHz had more obvious advantages than other frequency bands over the whole experiment process. This frequency range was consistent with the results of [PERSON]'s research [51], in which the acoustic emission frequency band was predominantly distributed at 100-300 kHz during the complete deformation. The wavelet transforms energy analysis can establish more accurately the characteristic frequency.  
The frequency band of 125-250 kHz can be defined as the dominant frequency band and the frequency band of 250-500 kHz as the suboptimal frequency band by the evolution process of the frequency band's proportion. These results were similar to those of [PERSON] et al. [52], where the main frequency ranges of AE were 220-280 kHz in the elastic stage and the average value was 123 kHz in the plastic stage, and they also pointed out that the main frequency decreased during the rockburst stage. The following results could have promising applications: Acoustic emission signals emerge in large numbers and the energy distribution coefficients of the dominant frequency band are concentrated above 0.4. The tendency in the proportion of dominant frequency band appears in continuous valley type and is maintained below 80%. The tendency to the proportion of suboptimal frequency band is continuous peak type and maintained above 20%. These results can be used as predicted features for the rockburst disaster in engineering fields.  
Due to the limitation of the experiment conditions, only the marble specimen was considered as the test object in this article. The experimental subjects will be extended in future research work, and the applicable conditions of wavelet energy evolution characteristics of acoustic emission signal will be further discussed, which will be considered for use in the field of rockburst disaster warning.  
Conceptualization, F.M.; Formal analysis, C.H.; Project administration, F.M.; Resources, F.M.; Software, C.H.; Writing--original draft, C.H.; Writing--review and editing, W.H. All authors have read and agreed to the published version of the manuscript.  
This research was funded by China University of Geosciences (Wuhan), grant number KH186619 and SKJ2017127.  
**Acknowledgments:** The authors would like to thank Guangxi University College of Civil Engineering and Architecture [PERSON]'s team and [PERSON] for their support.  
**Conflicts of Interest:** The authors declare no conflict of interest.