Stress Evolution Law of Surrounding Rock with Gob-Side Entry Retaining by Roof Cutting and Pressure Release in Composite Roof

Table 1

Mechanical parameters of surrounding rock.

Position	Rock stratum	Thickness (m)	Shear modulus (GPa)	Bulk modulus (GPa)	Cohesive force (MPa)	Internal friction (°)	Tensile strength (MPa)	Density kg/m^3
Roof	Medium sand	18.13	7.26	11.49	2.6	28	2.4	2450
	Siltstone	4.05	0.305	0.181	0.388	36	0.392	2400
	Fine grained sandstone	3.34	3.05	3.81	1	32	1.2	2400
	Mudstone	1.35	0.145	0.197	0.188	33	0.192	2360
	1^−2 upper coal	1.56	0.122	0.181	0.171	31	0.169	1400
	Siltstone	1.84	0.205	1.21	3.28	36	2.92	2300
Coal seam	1^−2 coal	2	0.122	0.181	0.171	31	0.169	1400
Floor	Siltstone	10	0.305	0.181	0.388	36	0.392	2400