Stability and Control of Retracement Channels in Thin Seam Working Faces with Soft Roof

Table 1

The parameters of coal and rock mass in numerical simulation.

Layer	Density (kg/m^3)	Bulk modulus (GPa)	Shear modulus (GPa)	Cohesion (MPa)	Internal friction angle (°)	Tensile strength (MPa)
Main roof	2800	10.80	5.50	4.40	33	6.00
Immediate roof	1900	3.67	2.20	2.40	29	1.50
Coal seam	1426	2.40	1.10	1.50	26	1.00
Floor	2495	8.45	3.90	5.10	33	8.00