Study on the Synchronous Instability Mechanism of the Coal Wall and Direct Roof of High Soft Coal Seam

Figure 4

Coal wall spalling type.

(a) Synchronous instability of the coal wall and roof

(b) Instability of the coal wall under high shear stress

(c) Instability of the coal wall affected by gangue

(d) Instability of the coal wall caused by tensile cracking