Investigation on the Movement and Fracture Characteristics of an Extra-Thick Hard Roof during Longwall Panel Extraction in the Yima Mining Area, China

Figure 6

Vertical displacement variation of five periodic caving of extra-thick roof.

(a) Initial equilibrium state

(b) The first periodic caving

(c) The second periodic caving

(d) The third periodic caving

(e) The fourth periodic caving

(f) The fifth periodic caving