During drilling the drill machine is set to drill at

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Unformatted text preview: gns to place the cut holes can be adopted. During drilling the drill machine is set to drill at the intended angle at which the raise is to be driven. For measuring angle instrument such as “Brunton” can be used. The central hole is usually drilled first. Each hole is collared for its initial 0.5 m using a little large dia. bit than the normal one for fixing the PVC stand pipe e.g. for a 57 mm dia. hole, a 65 mm dia. bit can be used to insert the standpipe. It is important to run the machine slowly while drilling these down holes and flushing them after every 0.5 m of drilling, to avoid rod and bit jamming. Once the hole/s get through to the lower level then it assists in draining out the drilling sludge to the lower level, and thereby, keeping the drilling site neat and tidy. The success of drilling lies in drilling the holes accurately without deviation. To achieve this, machine and its components including various clamps should be tightened before and during the drilling operation. The drilling accessories that are required at the site includes: Bits for normal drilling (e.g. 57 mm), collaring (e.g. 64 mm dia.) and reaming (e.g. 104 mm dia.); coupling and adopters; Extension drill steels; Rod and bit spanners; Lubricant; PVC stand pipes; Tapered wooden plugs; Crow bars; Spades; Picks etc. Raise correlation Before carrying blasting operation and shifting the drill to another site, the holes should be surveyed for their accuracy, if deviation exceeds the tolerable limits (not exceeding 1–2%), then additional drilling may be necessary to replace the deviated holes. © 2005 by Taylor & Francis Group, LLC 342 SURFACE AND UNDERGROUND EXCAVATIONS VII VIII VIII V VI VI II IV VII V I I V VII II III 2.5–4.0 m III IV VI V VIII VII VI VIII 2.5–4.0 m Legend – Charged holes 50–55 mm dia. – Uncharged holes 75–100 mm dia. – Charged holes 75–100 mm dia. – Roman letters indicate delay numbers Figure 13.8 Long hole raising – pattern of holes. Blowing and plugging the holes Since all the holes get through to the next lower level, hence, their plugging is necessary before charging them with the explosive. This is achieved by using the wooden plugs, or sometimes the polythene bags, or Hessian cloths, or old used jute bags (fig. 13.9(c)). To achieve a perfect plugging, first of all the plugging material is tied by a wire or rope and lowered down the hole till it gets through to the lower level. This plugging material suspended in this manner is then pulled up slowly while rock cuttings are also poured from the top into the hole simultaneously so that the bottom part of the hole gets plugged. However, the rope/wire should be pulled tight and tied to the anchor bolt fixed at the raise top to ensure proper plugging of the hole. This is a skilled operation and should be carried out by the trained personnel. The techniques used to plug the holes for drop raising, described in the following sections, can be also used. Charging and blasting After plugging, the holes are charged with e...
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