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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
operating cycle Working above
a pilot hole Raise drilling A reamer is
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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This document was uploaded on 02/12/2014.
- Spring '14
- The Land