Preliminary Discussion on Comprehensive Research Method for Rock Burst in Coal Mine Based on Newton’s Second Law

Table 2

Classification system for immediate roof [25].

Classification	I		II	III	IV
	Ia	Ib
	Instable		Moderately stable	Stable	Very stable
Lithology and structural property	Mudstone, shale; developed joints and fissures	Mudstone, carbonaceous mudstone; relatively developed joints and fissures	Compact mudstone, siltstone, sandy mudstone; undeveloped joints and fissures	Sandstone, limestone; few joints and fissures	Compact sandstone, limestone; extremely few joints and fissures
lr	≤4	4–8	8–18	18–28	28–50
Rc	27.94 ± 10.75	36 ± 25.75	46.3 ± 20	65.3 ± 33.7	89.4 ± 32.6
h0	0.26 ± 0.125	0.285 ± 0.13	0.51 ± 0.355	0.675 ± 0.34	0.72 ± 0.34
Rc·h0	<7.5	2.9–11.4	7.8–29.1	33–104	45.5–139.4
Cz	0.163 ± 0.064	0.273 ± 0.09	0.30 ± 0.12	0.43 ± 0.157	0.48 ± 0.11

Note. l_r: first caving span of immediate roof; R_c: uniaxial compressive strength; h₀: layer thickness; R_c·h₀: equivalent bending capacity; C_z: comprehensive weakening constant.