Permeability Enhancement and Gas Drainage Effect in Deep High Gassy Coal Seams via Long-Distance Pressure Relief Mining: A Case Study

Table 2

Coefficient for average height of the caved zone and WCFZ [40].

Strata lithology	Compressive strength (MPa)	Coefficients
		C1 (m^−1)	C2 (-)	C3 (m^−1)	C4 (-)
Strong and hard	>40	2.1	16	1.2	2
Medium strong	20–40	4.7	19	1.6	3.6
Soft and weak	<20	6.2	32	3.1	5