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

Figure 7

Comparison of main key strata absence and nonabsence recovery situation of 1⁻² upper coal and 1⁻² coal. (a) Absence of main key strata of 1⁻² upper coal seam mining. (b) Nonabsence of main key strata of 1⁻² up coal seam mining. (c) Absence of main key strata of 1⁻² coal seam mining. (d) Nonabsence of main key strata of 1⁻² coal.

(a)

(b)

(c)

(d)