# Research on the Outburst-Rockburst Coupling Disaster Law Based on True Triaxial Unloading Tests
## 5 Conclusions  
In this study, some physical tests and numerical simulation tests for outburst-rockburst coupling disasters were conducted. Additionally, the mechanical characteristics, meso crushing characteristics, and acoustic characteristics of the coal body under different gas pressures were analyzed. Based on real working conditions, the temporal and spatial evolution law of gas pressure and the migration characteristics of the crushed coal bodies were explored. The main conclusions were elucidated as follows.  
1. When the initial gas pressure increased from 0.6 MPa to 1.8 MPa (0.6 MPa, 0.9 MPa, 1.2 MPa, 1.5 MPa, and 1.8 MPa), the unloading stress on the unloading surface of the specimen during instability failure decreased by 7.94%, 8.34%, 17.38%, and 25.99%, respectively, compared with the corresponding previous gas pressure. The results demonstrated that the stress unloading degree of the coal body was negatively correlated with the initial gas pressure in the outburst-rockburst coupling disasters.
2. There was a \"double-peak\" distribution between the time domain characteristic parameter count and the energy of acoustic emission in the outburst-rockburst coupling disasters. More specifically, the peak value in a \"high-count and low-energy\" state corresponded to the dynamic \"small structure\" instability failure (coal and gas outburst) under the action of gas, while that in a \"low-count and high-energy\" state corresponded to the dynamic \"large structure\" instability failure (rockburst) under the action of three-dimensional stress.
3. In the outburst-rockburst coupling disaster process, the deterioration of gas promoted the development of tensile microcracks and shear microcracks in the coal body. After the occurrence of the rockburst, the further extension and penetration of these crackscontributed to the main crack of structural instability between the outburst opening and the deep coal body.
4. In the outburst-rockburst coupling disaster process, the outburst can be attributed to the small-scale failure in the shallow coal body, while the rockburst can be attributed to the large-scale failure in the deep coal body. Therefore, the \"cross\" shear failure of the coal body caused by the outburst-rockburst coupling disasters played a leading role in the coal and gas outburst.
5. The essence of the outburst-rockburst coupling disasters was identified by physical experiments and numerical simulation analyses. Specifically, the coal body reached the yield limit under the synergistic action of gas and crustal stress, and the gas degradation accelerated the development of coal cracks, thus leading to the occurrence of the outburst-rockburst coupling disasters.  
Conceptualization, L.S.; methodology, L.S., F.X., G.L. and K.X.; validation, F.X. and G.L.; formal analysis and investigation, L.S.; data curation, L.S. and K.X.; writing--original draft preparation, L.S.; writing--review and editing, L.S., F.X., G.L. and K.X.; supervision, F.X. and G.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Natural Science Foundation of Heilongjiang (ZD2021E006) and the National Natural Science Foundation (52174075).  
Not applicable.  
The data used to support the findings of this study are available from the corresponding author upon request.  
The authors declare that there are no conflicts of interest regarding the publication of this paper.