seemed to be indicative of recent seasonal melt/
operating efficiently, the melter was capable of
refreeze activity near the ice surface. The trash ice
producing water at close to 1900 L/hr (500 gal./
had little bearing strength and in areas would
hr). We discovered quickly that this method of fill
break under the pressure of a light utility truck
was wrong for two reasons. The fill operation
tires.
wasn't initiated until mid-November, which
The goal of this last reconnaissance of the ice is
meant that air temperatures and solar intensity
to make decisions about the final grade for the
were moderately high and rising significantly with
runway. In most cases, a single grade for the en-
time. Thus, the water acted as a heat sink and was
tire airstrip is neither practical nor necessary. A
not only reluctant to freeze, but actually caused
series of tabular segments, joined at a common
melting in much of the surrounding ice and snow.
elevation (or nearly so), will be adequate for nearly
Parts of the runway turned into a lake and re-
any aircraft that would use a glacial ice runway.
mained so until late in January. When the water
For the purpose of efficiency during grading, it
finally did start to freeze late in the season, the
probably does not make sense to design for tabu-
top of the water froze quickly, producing an insu-
lar segments any shorter than about 300 m (mea-
lating cap that drastically slowed the cooling and
sured along the length of the runway). Each
freezing of the bulk of the water. We discovered
segment should be level across the runway width
later (see Chapter 5) that this allowed large, ori-
(perpendicular to aircraft travel direction) but may
ented ice crystals to form, yielding very brittle,
be sloped along the length.
weak ice.
Large fill operations should be conducted only
at low temperatures, in the range of 10C or less.
Filling of low areas
In some situations, a single, or small number
Low areas should be prepared before water ap-
of, low areas may suggest a significant amount of
plication by essentially filling the entire basin with
grading to arrive at a plane surface. Filling such
snow and broken-up ice chunks. Construction de-
low areas is possible, although it is not as straight-
bris is ideal for this purpose, and the grading
forward as with earthwork. Filling low areas may
following initial strip-off should provide ample
be an attractive and economical alternative to hav-
material of an ideal mix of snow and ice. This fill
ing to grade huge areas just to accommodate a
material should be compacted as much as pos-
low-lying segment of ice.
sible by repeated passes with a vehicle. A bull-
At Pegasus, we filled an area that extended
dozer tractor with wide tracks is ideal since it will
between the 5000- and 7000-ft markers along the
have significant weight, and the passage of track-
runway and spanned the full width of the run-
guide rollers (boggies) acts to vibrate the fill, as-
way. (Distance along runways is most commonly
sisting in compaction.
given in multiples of 1000 ft [305 m]; thus we will
Once the low area is filled with compacted
use English units when referring to location along
snow and ice, it should be flooded slowly with
the length of the runway.) We approached this
fresh water from the edges. The goal is to slowly
task by massive flooding of the area using a por-
flood the interstices of the compacted snow and
table snow melter (Fig. 42); the snow melter was
ice, allowing air to escape and ensuring that no
diesel-fired and was fed by a bucket loader. Once
large pockets of unsaturated fill are trapped and
Figure 42. Portable snow melter.
40
Previous Page
