Coal mine surveying by Shurick A. T. (Adam Thomas) b. 1883 & Brinsmade Robert Bruce 1873-1936 & Donaldson Francis

Author:Shurick, A. T. (Adam Thomas), b. 1883 & Brinsmade, Robert Bruce, 1873-1936 & Donaldson, Francis
Language: eng
Format: epub
Tags: Mine surveying, Coal mines and mining
Publisher: New York : McGraw-Hill

of the seam; there is a thrust T, acting in the direction of dip, tending to make the roof slide over the face toward the empty space behind it.

The force T is evidenced in the fact that a fracture in the roof of a rise working " gapes," owing to the lower side having moved slightly down under the influence of T. Thus it is that falls of roof are more prevalent in rise workings than in any other; the side thrust T, not only quickly breaking up the roof, but also widening the joints the better to allow severed slabs to fall.

It is largely to this side thrust that we owe the production of slack which is one of the disadvantages of rise working; grinding is introduced, a far more effective slack producer than mere normal pressure.

The resultant action of the forces P and T on the coal may be best represented by the single force R. The direction of R cannot be accurately assigned, but it lies somewhere between the normal (P) and the perpendicular (shown dotted), and its position is probably somewhere as shown; its magnitude, by the parallelogram of forces is simply\/P 2 + T 2 . Considering the coal acted on by R aided by the weight of the coal itself, no further demonstration is needed of the reason of the ease experienced in working coal to the rise

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