Study on Occurrence Mechanism of Coal Pillar in L-Shaped Zone during Fully Mechanized Mining Period and Prevention Technology

Table 4

Testing result of roof samples impact tendency.

Name	Indexes			Determination result
Roof	Tensile strength (MPa)	Density (g/cm^3)	Elasticity modulus (GPa)	Weak impact tendency (II)
	3.459	2.626	6.508
	Thickness (m)	Overburden load (MPa)	Bending energy index
	40	0.0261	65.632