Es = 0.3 0.85
cies of the drive and bearing systems that are about
Es = 0.26 MN/m2 .
the same, the actual required power could be as
high as 5.2 kW (7 hp).
For a 0.6-m-diam. drum rotating at 120 rpm,
three 587-cm3/s (9.3 gpm) gear pumps operating
the tangential tip velocity of the cutters (ut) is 3.8
m/s. This speed was chosen as a maximum to pre-
at 17.2 MPa (max.) for powering the system. As
vent overacceleration and dispersal of cutting
the operational speeds of the various components
chips during machining. The power required to
on the reconfigured excavator would not need to
accelerate the chips should be low if the system is
be as high as originally designed, maximum flow
to be optimized, as the chips do not need to go
to these components was halved. The three con-
much beyond the face of the tunnel. To determine
trol circuits were fed by two electrically driven
pumps, a 328-cm3/s gear pump and a 574-cm3/s
this, the power required to accelerate the chip (PA)
needs to be compared to the power required to
gear pump, operating through a 50:50 splitter. A
660-cm3/s gear pump powered the drum, while a
cut the material (PR):
215-cm3/s gear pump powered the snowblower.
PA/PR ≈ ρut2/(2 Es) (Mellor 1977).
Flow rates for the drum and snowblower pumps
were derived from the motors used for each de-
Plugging in the values for the anticipated situa-
vice. The two control circuit pumps were tandemly
tion, we get:
mounted on one end of a double-shafted electric
motor, with the other two pumps tandemly
PA/PR ≈ 0.03.
mounted to the other end. Maximum power avail-
kW for the drum circuit. The next-largest size elec-
material disaggregation of about 3%, a very low
tric motor commercially available was a 37.3-kW
number. Other sources give much higher uncon-
model, which allows some room for upsizing the
fined compressive strengths for snow at the South
pumps. A high-efficiency 460-V motor of this size
Pole (Mellor 1964, Ramseier 1963), so this should
is used for this application. The motor and pumps
be a conservative number. In any case, this result
are protected from high startup torque and inrush
is quite acceptable for the tunneling application,
amperage with a Baldor/Lectron soft-starter, rated
where we don't want a lot of power going into
to 75 kW. A thorough description of all systems
accelerating the chips.
and components is included in the South Pole Tun-
To calculate the power required to disaggregate
neling System Operation and Maintenance Manuals,
the firn at the face of the tunnel, a production rate
a four-volume set of manuals written for NSF to
needs to be established. For our purposes, we used
accompany the system (Walsh et al. 1997).
3 m/h as our forward progress rate, for a produc-
All operator controls are contained within the
tion rate Q of 18 m3/hr (in situ). According to
tunneler cab. These include the following:
Tracks forward and reverse
PR = Es Q.
Creepfeed circuit for tracks: forward only
Cab swing (limited)
Plugging in values for the production rate and
Drum cutters rotate (toggle switch)
Drum pivot (toggle switch)
PR = 1.3 kW.
This is the theoretical cutting power requirement.
Snowblower impeller actuation (toggle
Actual power required will be higher due to sys-
The functions actuated by toggle switches are on/
off functions. The switches are mounted on a pen-
dant control hanging to the right of the operator,
Using combined inefficiencies of the hydraulic
and indicator lights on the control show which
system of about 50%, and mechanical inefficien-
function is energized (Fig. 10). Both the boom el-