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

Table 1

Rock mass parameters.

Lithology	mi	D	GSI	σt (MPa)	Em (GPa)	K (GPa)	G (GPa)	Φ (deg.)	c (MPa)	ν
Coarse sandstone	16	0.8	72	0.50	21.29	11.83	8.87	48.6	2.70	0.20
Fine sandstone	10	0.8	62	0.17	8.91	5.12	3.68	35.2	1.27	0.21
Siltstone	11	0.8	64	0.17	9.47	5.85	3.85	36.1	1.32	0.23
4# coal seam	5	0.8	40	0.03	1.90	1.22	0.77	16.3	0.42	0.24
Medium-fine sandstone	12	0.8	66	0.28	13.08	7.78	5.36	41.0	1.74	0.22
Kaolinite rock	7	0.8	53	0.07	4.42	2.73	1.80	25.3	0.75	0.23
Conglomerate	14	0.8	68	0.22	12.86	7.39	5.31	41.2	1.68	0.21
Fine sandstone	10	0.8	62	0.15	8.51	5.06	3.49	34.5	1.22	0.22
Carbonaceous mudstone	7	0.8	47	0.05	3.30	2.03	1.34	23.3	0.66	0.23
3# coal seam	5	0.8	33	0.01	1.20	0.77	0.49	13.2	0.31	0.24
Carbonaceous mudstone	7	0.8	47	0.05	3.29	2.03	1.34	23.3	0.66	0.23
Kaolinite rock	7	0.8	53	0.07	4.42	2.83	1.78	25.3	0.75	0.24
Medium-fine sandstone	12	0.8	66	0.28	13.10	7.53	5.41	41.0	1.75	0.21

Note: m_i is the constant of intact rock, D is the disturbance coefficient, and GSI is the evaluation parameters of fracture rock.