Grading Evaluation of Goaf Stability Based on Entropy and Normal Cloud Model

Table 1

Classification and assignment of quantitative indexes for goaf stability evaluation.

Indicator	Stability level
	Level I	Level II	Level III	Level IV
Rock quality (), %	>60	50∼60	40∼50	<40
Span (), m	<40	80∼40	80∼120	>120
Area (), m^2	<800	800∼1200	800∼1200	>2700
Height (), m	<8	8∼20	20∼30	>30
Depth (), m	<100	100∼200	200∼400	>400