S E C T I O N 5. G R O U T I N G E Q U I P M E N T
13.
INTRODUCTION. Guidance for selecting or approving the specialized
equipment necessary for a grouting project is provided below, and operational
principles for the equipment are outlined and related to job requirements.
14.
DRILLING
EQUIPMENT.
Percussion Drilling. Percussion drills are operated by air-driven
a.
h a m m e r s . The best known types are the jackhammer, drifter, and wagon
d r i l l . The drill proper consists of a hollow steel rod, fitted with a fixed or
detachable bit on one end and a shank on the other.
( i ) Operation. Percussion drills are used for drilling in rock. The
p e r c u s s i o n drill does not reciprocate. Its shank fits into and is held loosely
in the chuck at the forward end of the machine, where it is struck by a
h a m m e r - l i k e piston actuated by compressed air. The compressor capacity
necessary to operate a single-hammer drill ranges from 50 to 200 cfm, de-
pending upon the size of the drill cylinder and the pressure at which air is
supplied. During drilling the bit remains in close contact with the rock at
the bottom of the hole at all times except during the slight rebound caused by
impact of the hammer. Drills are provided with a mechanism that causes
the drill steel rod to rotate between blows of the hammer. Cuttings or sludge
are removed from the hole by air or water that passes through the machine,
down the hollow drill steel rod to the bottom of the hole, and then rises up
the hole to the surface. Removal of cuttings by water is preferred for grout-
hole drilling but is not mandatory. Jackhammer drills, due to their light
weight, are usually held in position by hand. Drifter-type drills are designed
for tripod or bar mounts. The wagon drill, as commercially available, is
comprised of a drill head mounted in leads that are supported on a track-,
w h e e l - , o r skid-mounted chassis.
(2) Application.
Percussion drilling produces acceptable grout holes
and, generally, is the most economical method of drilling shallow holes. This
advantage decreases with depth and disappears at depths from 75 to 125 ft
depending on the type of rock. In operation, the edges or wings of the bit
wear away so that a progressively smaller hole is drilled. Therefore, when
pertinent, the specifications should state the minimum acceptable size of
grout hole.
b . Rotary Drilling. Rotary drilling is the process of making a hole by
advancing a drilling bit attached to a rotating column of hollow drill pipe.
The drill pipe is turned by a motor at speeds ranging from a few hundred to
3 , 0 0 0 or more rpm. Pressure on the bit is applied hydraulically or mechan-
ically. Water is forced through the drill pipe to wash cuttings out of the hole.
Drill rigs vary in size from small lightweight machines capable of drilling
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