1·An arch having cusps in the intrados on either side of the apex.
在顶点两侧的内弧面上仍然有尖端的拱。
2·Finally, the coal-rock mass in the arch angle and apex is slided, and causes the distortion of local rock pressure, even induces dynamic hazards around working face.
拱角与拱顶煤岩滑落失稳，造成工作面局部压力畸变并诱发动力学灾害。