Mechanical Performances of Pressure Arch in Thick Bedrock during Shallow Coal Mining

Table 1

Material properties of coal and roof strata.

Name	Unit weight (kN/m^3)	Elastic modulus (GPa)	Poisson’s ratio	Cohesive strength (MPa)	Tensile strength (MPa)	Friction angle (°)
Sandstone	25.00	36.50	0.22	2.60	1.50	30
Coal	13.10	12.70	0.29	1.20	0.60	27
Siltstone	24.60	37.90	0.20	4.50	3	40