Pressure-Arching Characteristics in Roof Blocks during Shallow Coal Mining

Table 1

Physical and mechanical parameters of the materials.

Name	Unit weight (kN/m^3)	Elastic modulus (GPa)	Poisson’s ratio	Cohesive strength (MPa)	Tensile strength (MPa)	Friction angle (°)
Coarse sand-stone	24.3	35	0.23	5.5	4	33
Sand-stone	25.0	32	0.24	7.3	4.9	35
Mud-stone	22.4	23	0.15	2.5	1.7	30
Coal	13.1	15	0.29	0.79	0.57	27
Silt-stone	24.6	26	0.22	3.9	2.5	38