fully extended it is 35.5 m. At full system exten-
to be of limited value.
sion, the tubes must be collapsed and redeployed.
Access holes for power and chip removal are
Tube assemblies can be added as the tunneler
drilled using 30-cm-diam. single-flight augers. The
progresses, adding to the distance between setups.
auger is in 1-m lengths, and three assemblies have
They are narrow enough to pass by each other in
been made up using three segments each, for a
the tunnel. Each sliding tube joint has a set of metal
total length of 9 m. One segment is left for attach-
fingers and a silicone annular gasket that allows
ment to the augerhead when starting the hole. Two
sliding motion but little suction loss. A 30-cm sec-
augerheads are available; a short double bit head
tion of flexible pipe is attached between assem-
and a longer single bit head. The double bit head
blies to compensate for misalignment. The ends
is generally used because of its superior cutting
of the assemblies can be vertically adjusted using
built-in screw jacks. Although difficult starting, the
A 1-m-diam. backboring bit, designed and fab-
assemblies can be individually moved and posi-
ricated at CRREL, is also supplied. This bit is used
tioned by two people.
for forming emergency egress shafts from the sur-
To redirect the chips from horizontal to verti-
face to the tunnel. To use the backboring bit, a 30-
cal, a transition sled was fabricated. This is pri-
cm access hole must first be drilled at the location
marily a long flexible hose supported on a light-
of the egress shaft. Drill string is then lowered
weight, ski-mounted frame. The end of the hose
through the hole and the bit attached. The bit is
that connects to the expanding tubes has limited
then raised while it is spinning to enlarge the hole.
vertical freedom but a 1-m horizontal range. A
A 30-cm plug on the upper end of the bit keeps
blade-type pneumatic shut-off valve known as a
the bit centered in the access hole.
blast gate is incorporated into the end of the tube
to cut off airflow during maintenance operations.
The vertical connection end is attached to a hori-
zontally sliding adapter, which has a range of
about 15 cm. This allows alignment with the ver-
tical tubes lowered through a drilled access hole
from the surface. All connections between assem-
blies are made using Voss ring clamps.
A series of vertical tubes, lowered from the sur-
face using a tripod, guides the chips from the tun-
nel to the surface (Fig. 14). These tubes, ranging in
length from 3 m to 60 cm in length, were origi-
nally connected together using quarter-turn
latches. After several tubes became disconnected
and plunged down the access hole, the connec-
tions were redesigned to accept low-profile Voss
clamp rings. The lowest vertical pipe segment used
is 1.2 m long with a nested flexible hose for verti-
cal adjustment and alignment to the transition sled
adapter. Total vertical adjustment is 1 m. At the
surface, a tube with a flange is used to anchor the
vertical tube assembly. A flexible hose and sliding
tube assembly connects the fan to the vertical
The drill rig is a Simco 2400 SK-1 trailer-
mounted drill with special CRREL-designed skis
to allow easy transport on snow (Fig. 15). The con-
trols have been slightly modified to allow speed
control when operating the up-feed as well as the
down-feed of the drill head traverse. Heaters have
Figure 14. Installing vertical chip conveyance tubes.
been added to the hydraulic tank but have proven