As the coal in a longwall panel is being extracted by the shearer slice by slice, the surrounding strata are forced to move toward and attempt to fill the voids left by the extracted coal. When a longwall panel of sufficient width and length is excavated, the overburden roof strata are disturbed in order of severity from the immediate roof toward the surface. The formation of separate zones in the overburden has been reproduced in laboratory experiments. When the fall height of the falling strata is more than 2.0–2.5 times the thickness of the falling strata, the strata will fall rapidly and rotate during falling, resulting in irregular rock fragments on the floor. There are many ways of classifying the roof for purpose of powered support evaluation for longwall mining. From the production point of view, the strata immediately above the coal seam top can be divided into three groups, that is, unstable, medium stable, and stable.