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The same procedure is repeated while charging rest of

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Unformatted text preview: i.e. the other half is then charged. The hole is then stemmed, for a length of 1–2 m or so, using suitable material. The same procedure is repeated while charging rest of the holes. This may be noted that the low density explosives © 2005 by Taylor & Francis Group, LLC EXCAVATIONS IN UPWARD DIRECTION – RAISING 347 such as ANFO is not suitable for this technique, and therefore usually slurry explosives, which can also be used in the watery holes, are used. Use of double deck or multi deck charging has been tried successfully in some mines but during stoping operations its application is common. Performance: Since drilling and blasting are the independent operations so better productivity can be achieved by this technique. While drilling performance depends upon the usual parameters such as rock factor (type of strata), operating factors (drill’s power, blow energy, speed and flushing mechanism), drill hole factors (hole dia., length and inclination) and service factors (working conditions, skill of operator etc.). But after completion of drilling, by a trained crew, a blasting round of 3–4 m/shift or at least a round in the alternate shifts can be achieved. Scope, advantages and limitations: This technique has got the same scope of its application, advantages and limitations as the long hole raising practice, described in the preceding section. In addition, there is a scope to reduce the cost further as a better drill factor, powder factor and productivity can be achieved by this technique. Longer raises up to 80 m or so have been driven successfully, however, the only limitation is the requirement to use the same drilling equipment in the stoping operations too, in order to justify the investment made. 13.11 RAISING BY THE APPLICATION OF RAISE BORERS11 This is another technique (fig. 13.4(f))11 that can be applied to drive a raise between two levels. Using this technique raise up to 910 m length and 30° to vertical (usually steeper than 45°) of 0.9 m to 3.7 m cross section can be driven. This is the usual range but Robbins – Atlas Copco raise borers have even cross this range (table 13.2). Raises have been drilled successfully even in a relatively poor grounds. A circular configuration is obtained by this technique without application of drilling and blasting. The machine is setup at the top and a pilot hole of 225 to 250 mm dia. is first drilled down to get through into the lower level, as shown in figure 13.10. Then a large reamer bit is put on at the bottom of the drill rod and the raise is reamed to the desired dia. up to the upper level. The pilot hole also provides information about the type of strata to be encountered and helps in driving the raise accurately. In case of large deviation, the Raise drill operating cycle Working above or below ground, the machine drills a pilot hole Raise drilling A reamer is attached in place of drill bit The raise drill pulls the reamer toward itself. Tailings fall down the shaft and are removed Figure 13.10 Driving vertical raise using raise bo...
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