The surrounding rock of roadway is a compound structure consisted of roof, floor and sides. The sides of extraction opening are the weak coal mass, which affect the stability of floor directly.
巷道围岩是由顶板、底板、两帮组成的复合结构体，回采巷道两帮为软弱煤体，直接影响到底板的稳定性。
3
Up a dark, winding staircase lies a shabby room, lit only by a small window set into the sloping roof which throws a weak square of daylight onto the bare wooden floor beneath.