Chicago : Engineering and Contracting Pub. Co. · leaf 415
ature and slight \.inations in the toughness of the ground andthe si/e of the workings necessitate diffeienth placed relief holes for successive cuts. The most important rule to be observed,placing holes is that the determining factornot the distance apart of the starting points.-the holes but the… … Fig. 3. while between the bottom of the cuttingand the bottom of the squaring-up holes isft. of rock, so that in hard ground the _would not break. Fxpericnce in any variof rock will show what unit may be figuiupon for the dividing distance of the bott<of the hole, usually 2 or 2% ft. The…
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