Angle of draw
Angle of draw
In coal mine subsidence, this angle is assumed to bisect the angle between the vertical and the angle of repose of the material and is 20 degrees for flat seams. For dipping seams, the angle of break increases, being 35.8 degrees from the vertical for a 40 degrees dip. The main break occurs over the seam at an angle from the vertical equal to half the dip.
The angle between the limit line and the vertical
The angle made by the cave boundary with the vertical, i.e. the complement of the angle of break.