Mechanism of Secondary Breakage in the Overlying Strata during Repetitious Mining of an Ultrathick Coal Seam in Design Stage

Figure 3

Structural evolution of overburden when slicing mining (SM) a UTCS: (a) first SM; (b) second SM; (c) third SM; (d) fourth SM; (e) fifth SM; (f) sixth SM.

(a)

(b)

(c)

(d)

(e)

(f)