Meanwhile, it is positioned at triangle area of the stope roof arch, thus the tunnel roof cannot inbreak along with the mining face roof caving, and also a hanging arch is formed on the back of the work face, which becomes universally
When working face and nose move 4 coal cutters, namely, 3.2 m forward, the coals on top inside the setting roadway begin to inbreak. Meanwhile, the limestone on the upper roof gradually starts to collapse.