Permeability Enhancement of Coal Seam by Lower Protective Layer Mining for Gas Outburst Prevention

Figure 6

Stress field and permeability evolution law of the protected layer in #3 coal seam: working face of #8 coal seam advancing (a) 40 m, (b) 80 m, (c) 120 m, and (d) 480 m.

(a)

(b)

(c)

(d)