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Unformatted text preview: operations in underground mines too. This terminology to designate production drilling will be used throughout this book. Thus, to dislodge the rock
from its rock-massif use of suitable drills, explosives and blasting techniques, is made.
This task can also be accomplished without using explosives, which will be dealt in the
following chapters. This chapter deals with the drills and their utilities in detail.
The drilling with few exceptions such as: exploration, to provide drainage, in fixing rock
bolts, in stabilizing slopes and to test foundations, is employed in mining and tunneling
for placement of explosives. Figure 4.1, illustrates the application of this operation.
4.4 OPERATING COMPONENTS OF THE DRILLING SYSTEM
There are four main functional components of a drilling system, working in the following manner to attack the rock as illustrated in figure 4.2(d).2
1. The drill: it acts as prime mover converting the original form of energy that could
be fluid, pneumatic or electric into the mechanical energy to actuate the system.
2. The rod (or drill steel, stem or pipe): it transmits the energy from prime mover to
the bit or applicator.
3. The bit: it is the applicator of energy attacking the rock mechanically to achieve
4. The circulation fluid: it cleans the hole, cools the bit, and at times stabilizes the
hole. It supports the penetration through removal of cuttings. Air, water or © 2005 by Taylor & Francis Group, LLC DRILLING 63 (a) Flushing (air/water) Tons Rotation Percussion
chips Feed Bit
Drill rod (d) Principle of percussive drilling Flushing
drilling (b) Water flushing Air flushing
0.4% - 1.0m/s 15% - 30m/s (c) Chips Chips Rotary crushing Rotary cutting Augur drilling Types of rock
Chalk Limestone Granite Taconite Sandstone
Compressive strength in bar
500 1000 1500 2500 Quartzite
3000 4000 5000 (e) Flushing principle Percussive drilling
Rotary crushing - cemented carbide roller bits
Rotary crushing - steel - toothed roller bits
Rotary abrasive drilling
(f) Application of drills of different type based on
rocks of different types Figure 4.2 Drilling principles, mechanism and flushing systems. Functional components of a
drilling system also shown. (Courtesy: Atlas Copco)1 sometimes mud can be used for this purpose. It flushes the cuttings as per the principle illustrated in figure 4.2(e).1 Figure 4.2 (e) also shows the flushing velocities.
4.5 MECHANICS OF ROCK PENETRATION
Using the drills the rock is attacked mechanically, as shown in figure 4.2(a),1 either by
percussive or rotary actions. Combinations (roller bit, rotary-percussion) of these two
methods are also used. The resulting action of the bit in each case is almost similar i.e.
crushing and chipping; what differs mainly is that the crushing action predominates in
percussion drilling and chipping action in the rotary drilling, and a hybrid action in the
combination of the two systems. Based on this logic the drills are manufactured as
percussive, rotary-percussive and rotary. Classification based on this logic is presented in figure 4.3.
4.5.1 TOP-HAMMER DRILLING
In this system the top-hammer’s piston hits the shank adapter and creates a shock
wave, which is transmitted through the drill string to the bit (fig. 4.2(a)). The energy © 2005 by Taylor & Francis Group, LLC 64 SURFACE AND UNDERGROUND EXCAVATIONS ROCK DRILLS PERCUSSIVE ROTARY Top-hammer
(Conventional drills) Down-the-hole
(DTH drills) Crushing Shearing Impact mechanism
outside the hole &
rotation ratchet type,
or independent and
outside the hole. Impact mechanism
inside hole, rotation
independent. Roller bit Drag bit Medium-hard, hard
rocks in u/g mines
and tunnels. Medium-hard, hard
rocks in surface &...
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