ROOF SUPPORT
Generally Weight of the rock in coal mining area exerts a pressure of nearly 0.2kg/cm2 for every meter depth from the surface.Rocks are called massive when bedding planes are the 75mm to1.2meter and rock called fluggy when bedding planes less than 75mm.When working and driving road way the immediate roof called about 6m.above the seam and immediate fllor some 3m.*below the seam.Angle of draw-It is the angle between the vertical and final line of break. Comprehensive or crushing strength of coal many consider 2.25kg/mm2or1.5ton/sq inch. Comprehensive strength of sand stone is nearly13.5kg/mm2.Best rrof called in stone(eg-Girdhi Coal Fields).Shale roof is unrelible.0.6meter of coal intact near ashaly roof during development of mine.