Study of the Stability Control of the Rock Surrounding Double-Key Strata Recovery Roadways in Shallow Seams

Table 2

Values of the coefficients C₁ and C₂ for various stratum strengths.

Type of immediate roof	Uniaxial compressive strength (MPa)	Coefficient
		C1	C2
Strong and hard	>40	2.1	16
Medium strong	20∼40	4.7	19
Soft and weak	<20	6.2	32

Σh is the height of the caving zone, and m is the mining height.