Mechanism of Coal Burst and Prevention Practice in Deep Asymmetric Isolated Coal Pillar: A Case Study from YaoQiao Coal Mine

Table 7

Relation between negative velocity anomalies and coal burst risk level.

Weakened degree	Weakening characteristics	Negative velocity anomaly, An (%)	Stress reduction degree
0	None	0∼−7.5	<0.25
−1	Weak	−7.5∼−15	0.25∼0.55
−2	Middle	−15∼−25	0.55∼0.8
−3	Strong	<−25	>0.8