TM 5-852-2/AFR 88-19, Vol. 2
CHAPTER 4
GROUND SURVEYS
4-1. General.
a rapid means of determining the location of the
upper surface of permafrost over a large area. It is
By using the overlays individually and in super-
necessary to supplement probings by explorations in
position, it is possible to design a ground sampling
which soil samples are obtained for visual
program. This program should take advantage of
classification or laboratory tests. Unfrozen soils are
the fact that within each pattern boundary the
sampled using techniques and equipment similar to
conditions are generally uniform and that extensive
those developed for the temperate zone (see App I
sampling is not required within those boundaries.
of TM 5-818-1).
However, field investigation should be undertaken
(3) Samples of frozen soils suitable for water
to verify that conditions in the area are as
content and classification tests can be obtained by
interpreted from the photos.
power auger. Tungsten carbide cutting teeth on the
base of augers give satisfactory service, if frozen
4-2. Ground reconnaissance.
material does not contain an excessive amount of
Based on the terrain categories defined by air-photo
cobbles or large boulders. It is not always possible
analysis, a field study should be started. Inspection
by use of a power auger to obtain sufficiently
of the selected area from the ground is the only
undisturbed samples for determination of the
certain method of getting all necessary information
intensity of ice segregation in soils. Relatively
for a particular site. It should include observations
undisturbed samples of frozen silts, clays, and some
of soil, snow cover, vegetation, ground water,
fine, saturated sands can be obtained by drive
surface water, local sources of construction
sampling using a pipe with a tempered, sharpened
materials, and other pertinent information. Much
cutting edge, or soil sampling tube, or by rotary
valuable information regarding floods, icings,
drilling, using tungsten carbide saw-toothed core
earthquakes, and landslides can often be obtained
bits or diamond core bits.
from local inhabitants. For ground reconnaissance,
(4) Soil that may appear to be unfrozen, espe-
hand equipment, such as hand levels and augers, are
cially in auger cuttings, may actually contain frozen
generally used. For more comprehensive surveys,
water. If there is any doubt, the sample should be
conventional surveying methods are employed. The
examined with great care. The soil should be
extent and precision of the information to be
warmed and carefully examined for a marked loss in
obtained is determined by professional judgment.
strength accompanied by an apparent marked
a. Subsurface explorations. In the evaluation of
increase in water content. Such behavior definitely
a potential site in a permafrost area, the site location
indicates that the sample initially contained frozen
in relation to local topography and land forms is an
water.
important factor in helping to understand the
(5) Borings are generally done without the use
character and nature of subsurface materials (see
of casing except as necessary to prevent caving in
TM 5-852-8/AFM 88-19, Vol. 8). Data can be
the thawed portions of the hole. The test boring may
obtained by sounding rods and by percussion,
be advanced from one sampling depth to the next
rotary, and auger drilling. Adequate exploration,
either by churn drilling, using water for drilling fluid
however, requires fairly continuous and undisturbed
with additives as necessary to prevent freezing, or
samples.
by rotary drilling, with a roller bit using precooled
(1) Explorations made during the late summer
compressed air to blow the cuttings to the surface.
or early fall may be necessary to determine the depth
The use of salt to depress the freezing point of the
to the permafrost table, the location of which has an
drilling fluid to a sufficiently low temperature for
important role in most design studies and
drilling and coring requires a considerable amount
construction planning. From the standpoint of
of salt, which dissolves ice in samples and often
equipment mobility, the best conditions for
causes skin irritations. Arctic grade diesel fuel
reconnaissance and preliminary explorations in the
cooled by ambient air in winter or by mechanical
more remote areas usually exist during the winter,
refrigeration in summer has yielded mechanically
while the ground surface is frozen.
and thermally undisturbed core samples of a wide
(2) Probings by driving rods by hand or by use
variety of frozen soils and rocks. The use of chilled
of a drill rig near the end of the thawing period are
diesel fuel as the drilling fluid may be disagreeable
4-1
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