Local Fall - This is also called as first roof fall. In this type of fall the lower strata of immediate roof separate and fall in the underground opening . These fall are normally takes place soon after withdrawn of supports is called local fall . These fall takes place within 24 hours to 48 hours of withdrawal of supports. These type of falls normally does not extend to the surface.
Main Fall : When the area of extraction or could area of opening is nearly equal to or more than the square of the depth, the cracks due to pillar extraction extend up to surface. The roof fall which affects the surface is known as the main fall. Main fall takes place long after the first roof fall or local fall in the de pillaring district.
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