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Shallow Coring
Hand Augers
The hand auger is the most basic of
the mechanical drills and is driven from the surface
by a series of extensions that are added as drilling
proceeds into the ice. The drill, like all other coring
drills, has to be retrieved each time a core section
is recovered. The hand augers come in two different diameters:
3"
and 4". The 3-inch model takes cores 1 m long; the 4-inch
auger as currently configured will take only half-meter
cores. "Core dogs" serve both to break and to hold the
core.
These basic hand drills have undergone
adaptations for specific purposes. The "Prairie Dog" modification
includes a stationary outer barrel to allow operations
in solid ice as well as firn. The "Sidewinder" is driven
by an electric motor, utilizing solar power or a small
generator, with a winch to help retrieve the drill string.
The depth limit for hand auger systems
(including the Sidewinder and Prairie Dog versions) is
about 40 meters but most hand-coring operations are significantly
shallower.
A recent addition to our collection
of hand augers is a small, motor driven, hand-held coring
drill that quickly collects a short, 2 inch diameter
core in solid ice. It has two barrels, 15 cm long and
50 cm long, respectively. This device was designed and
produced at ICDS -UW in response to the requirements
of one of our many clients.
Pico
Hand Drill Manual
4-Inch Drills
Our old standby is the 4-inch electromechanical
drill, a cable-suspended and motorized version of the
hand auger. An electric motor drive is mounted directly
to the drill with torque reaction provided by bowed leaf
springs attached to the upper end of the drill. An electrothermal
version of this drill, which melts an annulus around
the core, can be substituted for use in ice warmer than
-10º
C. Both versions use core dogs to break the core off
and hold it for retrieval. Borehole depth is limited
by closure due to pressure acting across the borehole
walls. In ice at -2C the limit is about 200 m; as the
ice gets colder the depth limit rapidly increases. Core
quality often deteriorates for some distance below the
firn-ice transition; in this zone the ice becomes brittle
due to bubble pressure and other factors.
This drill and its winch can be disassembled
for transport into remote regions, and has been used
to retrieve cores up to 309 meters deep at altitudes
over 7000 meters. The drill has also been used with solar
panels.
Eclipse Drills
The Eclipse drill, manufactured by Icefield
Instruments in Whitehorse, Yukon, operates on the same
general principles as the 4-inch drill but is more sophisticated.
Its control system allows improved control of depth,
cutter and winching speed, and direction. There are displays
of motor speed, current, and voltage as well as centimeter-accuracy
drill depth, lockouts to prevent motor damage due to
current pulses, and magnetic brakes that engage automatically
if the power should fail. The Eclipse drill is designed
to be disassembled into easier-to-transport components,
none weighing more than about 25 kg. The Eclipse drill
takes a 3.25-inch core. An Eclipse Drill has been used
to core to a depth of 346 meters at the Eclipse Ice Field,
Yukon. ICDS has two of these drills in its inventory.
2-Inch Drill
In Autumn 2003, ICDS acquired a 2-inch
coring drill made by Glacier Data in Fairbanks, Alaska.
This drill is much smaller and lighter than the Eclipse
Drill. The 2-Inch Drill is equipped with an outer barrel
so as to make it possible to operate in solid ice as
well as firn. The drill is powered from the surface using
batteries, solar cells or generator system, and is suspended
on an electromechanical cable. The cable is wound and
payed-out using a hand-powered winch. Total weight of
the drill, excluding power source, is 200 pounds. The
maximum depth to which this model of drill has cored
is 42 meters.
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