TM 5-852-4/AFM 88-19, Chap. 4
CHAPTER 6
CONSTRUCTION CONSIDERATIONS
138
described by Dickens and Gray , it is possible to
6-1. Effect of construction procedures on design.
construct footing type foundations in the summer months
a. Design decisions must be approached not
with satisfactory results; however, such type construction
as isolated technical questions but as a system of
may involve quite different labor, materials, and
interrelated elements under broad design, construction,
equipment requirements with different transportation,
operational and maintenance facility requirements.
housing, maintenance and supply problems than would
b. The tentative construction schedule and
apply in winter.
procedures should be kept in mind during all phases of
d. Through proper design and construction, a
the design procedure and should provide input
foundation may be installed in permafrost with minimum
influencing design decisions. The facility location and its
disturbance to the thermal regime and with rapid healing
environment, the relative urgency of the project and of
of thermal damage caused by construction. However,
desired completion data to meet user needs and the type
the construction procedure adopted will be a major factor
and scope of the effort will indicate the type and amount
in determining the amount of environmental damage and
of construction to be accomplished under adverse
therefore the damage-corrective provisions in the plans
seasonal conditions. The progress and efficiency of the
and specifications, as well as costs.
work during such periods will depend on how well the
designer has anticipated and adapted the design to the
6-2. Excavation.
conditions.
c. Site accessibility and working conditions
a. In permafrost areas, excavation should be
avoided as much as possible in the foundation design
may affect choice of type of foundations. Access to
because of the increased disturbance of the thermal
remote sites by sea or river may be possible only during
regime and the increased effort required when frozen
a short period in the summer. In permafrost areas
ground must be handled.
During the summer,
overland access may be possible only in winter after the
excavations in finegrained permafrost for placement of
annual thaw zone has solidly refrozen. Aircraft landing
footings may experience very rapid thaw and softening
facilities may severely restrict the size and type of aircraft
on exposure and it is almost impossible to install footings
which can land at the site. This may limit the sizes and
and to complete backfill under these conditions without
types of construction equipment which can be brought in
experiencing at least some short-term settlement of the
by air. For small to moderate size construction jobs, the
base of the footing, even though gravel fill or insulation is
cost of improving the aircraft landing facilities may be
placed quickly at the bottom of the excavation to
prohibitive. Landings on ice cannot be made during the
minimize this effect. Therefore, such excavations are
ice break-up and early freeze-up periods. Heavy aircraft
much more easily accomplished when air temperatures
cannot land on floating ice until middle or even late
are below freezing, preferably in the early fall when the
winter. Tractor train operations on ice are similarly
annual frost zone is completely thawed and most easily
limited. Access roads and granular working mats may
excavated through. At subarctic locations, excavation of
be easy to place in winter when the terrain is frozen but
soil above the permafrost table may not be a major
much more difficult to construct in summer. On the other
problem during the early part of the freezing season,
hand, if the facility construction is small and can be
especially if ground-freezing is minimized by an
completed in winter, roads and working mats may not be
insulating cover of snow, moss, or other material. As the
needed at all except for facility operational purposes.
winter progresses and depth of freezing increases,
Under proper scheduling, pile installation equipment can
excavation becomes more difficult, unless the excavated
work on compacted snow or frozen ground in late winter
materials are very coarse and well-drained. Winter
or early spring at maximum efficiency, without the use of
construction involving excavation is handicapped by
granular work mats. As described in paragraph 4-8d,
frozen ground conditions, the difficulties of operation of
this same period of maximum cooling of the ground in
equipment and handling of frozen materials at very low
depth (February through May) is the most effective time
temperatures, reduction of daylight hours and work
for installation of slurried piles intended to freeze back
season, and lowered worker efficiency at low
naturally. However, if it is not possible to install the piles
temperatures.
in the critical months and it is a marginal permafrost
b. Special equipment such as heavy rippers,
area, it will be necessary to use artificial refrigeration to
systematic drilling and blasting or possibly pre-thawing of
assist freezeback or to choose another type of
foundation, and this must be reflected in the plans,
specifications and cost estimates.
.As has been
6-1
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