Study on Roof Breakage-Induced Roadway Coal Burst in an Extrathick Steeply Inclined Coal Seam

Table 3

Relation between the wave velocity anomaly and the stress concentration level.

Coal burst risk index	Stress concentration level	Wave velocity anomaly An (%)
0	None	<5
1	Weak	5∼15
2	Moderate	15∼25
3	Strong	>25