Influence of Valleys Terrain on Pressure of Fully Mechanized Working Faces in Shallow Coal Seams

Table 4

Parameters of the indoor physical model.

Lithology	Thickness (cm)	Compression strength (MPa)	Volume-weight (KN/m^3)	Water ratio
Unconsolidated formation	36	31.2	25	1/8
Main key stratum	6	34.3	28	1/6
Immediate roof	9	29.9	25	1/8
1^−2 upper coal seam	3.5	12.0	14	1/8
Subcritical strata	5	34.0	28	1/8
Immediate roof	6	29.8	25	1/8
1^−2 coal seam	4.5	10	14	1/8