Failure Mechanism and Control of Lower Retracement Channel in Close-Distance Double-Thick Coal Seams

Table 3

Coal pillar safety factor.

Safety factor (FOS)	0 ≤ FOS < 0.8	0.8 ≤ FOS ≤ 1	1 < FOS ≤ 1.5	FOS ≥ 2
Coal pillar state	Unstable	Critical stable	Stable	Absolute stable