Influence of Coal Caving Time and Tail Beam Swing Angle on the Evolution of the Coal Gangue Boundary Line during Top Coal Caving

Table 2

Material interaction parameters.

Interaction parameters	Coal-coal	Coal-gangue	Coal-steel	Gangue-gangue	Gangue-steel
Coefficient of restitution	0.64	0.645	0.65	0.645	0.6
Coefficient of static friction	0.329	0.315	0.46	0.3	0.5
Coefficient of rolling friction	0.036	0.028	0.032	0.02	0.01