Analysis of the Influence of Upper Protective Layer Mining on the Effect of Pressure Relief and Protection of Coal and Rock Masses between the Lower Overburden Layers

Table 2

Mechanical parameters of roof and floor rock strata at the coal seam.

Lithology	Density (kg/m^3)	Bulk modulus (GPa)	Shear modulus (GPa)	Tensile strength (MPa)	Cohesion (MPa)	Internal friction angle (°)
Sandy mudstone	2605	2.16	1.69	0.38	2.6	27
Siltstone	3211	10.48	8.19	0.44	2.85	28
Quartz sandstone	2600	21.03	13.53	0.47	2.8	30
9-2# coal	1300	0.83	0.38	0.29	1.8	24
Mudstone	2554	3.23	1.85	0.32	2.2	28
9-1# coal	1300	0.83	0.38	0.29	1.8	24
Mudstone	2554	3.23	1.85	0.32	2.2	28
Siltstone	3211	10.48	8.19	0.44	2.85	28
Sandy mudstone	2605	2.16	1.69	0.38	2.6	27
8# coal	1300	0.83	0.38	0.29	1.8	24
Mudstone	2554	3.23	1.85	0.32	2.2	28