Safety Mining Technology of Coal Seams in Weathered Zone Based on Ground J-Type Pregrouting Reinforcement

Figure 4

Movement law of the overburden strata when two hard rocks exist: advancing distances of the working face are (a) 35 m, (b) 45 m, (c) 50 m, and (d) 90 m.

(a)

(b)

(c)

(d)