## 5 Conclusions  
In this paper, the stress-strain relationship and dynamic failure characteristics of coal samples under different mining-induced stress disturbances are systematically studied by using a self-developed true-triaxial coal-rock dynamic characteristic test system. The coal crater's formation mechanism and the coal burst's triggering mechanism are discussed. The main conclusions are as follows:  
1. Disturbance duration of the coal sample under quasi-static load decreases with the increase of disturbance rate. The peak stress is not affected by the disturbance rate. It increases first and then decreases with the disturbance stress level. The peak strain increases with the increase in stress level. It is beneficial for coal samples to accumulate elastic energy at a relatively stable rate, the corresponding rock burst pit depth is the  
Figure 14: Triggering mechanism of coal burst under different disturbing mining-induced stress.  
largest, and the most debris is formed. It corresponds to a high static load dominant coal burst.
2. Disturbance duration and peak stress of coal samples under cyclic loading decrease with cyclic amplitude and frequency increase. The peak strain increased gradually with the increase of cyclic amplitude. It increased first and then decreased with the increase of peak frequency. The cyclic mining disturbance load is more likely to cause the coal sample to produce flaky or layered damage on the surface of the free surface. The cyclic load leads to the permanent deformation of the coal sample, corresponding to a seismic fatigue load dominant coal burst.
3. The disturbance duration and stress peak of the coal sample under transient load decrease with the increase of transient increment and disturbance stress level. The peak strain decreases linearly with the increase of transient increment and increases with the increase of stress level. The dynamic impact failure characteristics caused by the transient mining disturbance load are superficial. Because the load is generated instantaneously, the energy accumulation and release speed are also speedy. After reaching a certain degree of damage, a violent spray is generated, and the final damage degree is intense. It corresponds to the instantaneous impact dynamic load dominant coal burst.  
In conclusion, the mechanism of coal burst is affected by both quasi-static load, cyclic load, and transient load, and the combination of these three can deepen the understanding of the triggering mechanism of coal bursts and provide theoretical guidance for the further plan of monitoring and prevention.  
Conceptualization, J.B.; project administration, L.D.; software, X.L.; writing, J.B. and K.W.; investigation, J.C., Y.C. and J.K. All authors have read and agreed to the published version of the manuscript.  
This research was carried out with the funded projects: National Natural Science Foundation of China (Grant No. 51874292, 51934007) and National Key Research and Development Program of China (Grant No. 2016 YFC0801403). The first author also acknowledges the Postgraduate Research & Practice Innovation Program of Jiangsu Province (KYCX21_2342).  
Not applicable.  
The authors confirm that the data supporting the findings of this study are available within the article.  
We appreciate the support from the State Key Laboratory of Coal Resources and Safe Mining, and Shaanxi Zhengtong Coal Industry Co., Ltd.  
The authors declare that there are no conflict with this publication.