TM 5-852-4/AFM 88-19, Chap. 4
d. Simplified example of selection of
estimated together with related effects of the changes on
foundation type in an area of continuous permafrost.
subdrainage in the area and the thermal regime in the
ground.
(1) Facility Requirements
(g) Preferred practice is to aim as
One story permanent facility, above
closely as practicable at the method in (1) above, but
surface.
with knowledge that construction must inevitably effect
40 lb/ft' floor load capacity.
some changes in accordance with the method in (2)
72F room temperature, year-round No
above. Under the latter, design should aim at making
special thermal loads.
the changes in thermal regime determinate. Where
(2) Site Data Very remote site, continuous
conditions are favorable, the method in (3) above may
permafrost.
sometimes obviate the need for special foundation
No local trained labor or materials.
Mean permafrost temperature + 12 F.
structural design, although the requisite conditions for
employing this technique occur somewhat rarely.
Thawing index = 700.
(h) Unless foundation soils are clean
Freezing index = 8000.
granular materials which will not produce significant frost
Permafrost thickness = 1700 feet.
heave or settlement with fluctuations of thermal regime, it
Overburden: 90 ft glacial till, silty gravel
is accepted practice to support structures either entirely
GMVr, containing ice wedges, over
on top of the annual frost zone or entirely in the
bedrock.
underlying permafrost zone using piles or other means to
Anticipated settlement of overburden on
transmit structure loads through the annual frost zone.
thaw = 2 in./ft of thaw depth.
c. Simplified example of selection of
(3) Because permafrost is very deep and
foundation type in an area of discontinuous permafrost.
continuous, as well as containing substantial ground ice,
(1) Facility Requirements
the alternative "Modification of Foundation Conditions
One story permanent facility, above
Prior to Construction" (fig. 4-2) is impractical and
surface. 250 Ib/ft' minimum floor load
inapplicable. Permafrost temperature is low enough so
capacity.
that a thermally stable design is readily achievable.
72ƒ F normal room temperature.
Under the foundation conditions, the alternative
No special thermal loads.
"Acceptance of Thermal Regime Changes to be Caused
(2) Site Data
by Construction and Facility" is impractical for a
Within 5 miles of a city, in discontinuous
permanent facility. Therefore, the possible designs
permafrost region.
shown under "Existing Thermal Regime to be
Construction materials, labor, equipment,
Maintained" should be considered. For the light floor
transportation all readily available.
loading the ducted foundation and the rigid structural
Clean, bank run gravel borrow available 3
base options are too heavy and costly and are
miles from site.
inappropriate. Since there is no special thermal load,
Mean permafrost temperature 300F.
permafrost temperature is low, and the structure is
Thawing index = 5700.
above-surface and can have a ventilated foundation,
Permafrost thickness = 200 ft continuous
there is no need for artificial refrigeration. Therefore,
over site.
design alternatives for permanent type foundation are
Overburden: 5 ft silt, non-plastic ML-Vs,
piling, spread footings, and post and pad. Choice can be
over clean, frozen, thaw-stable sandy
made on basis of cost after development of details for
gravels, GW-Nbn, extending to bedrock at
each of these types to the degree needed for resolution.
210 feet.
4-2. Control of heat transfer and degradation.
No ice wedges. Anticipated settlement of
a. General.
silt on thaw = 1 1/2 in./ft.
(1) Frost and permafrost conditions,
(3) Since there is only 5 feet of thaw-
thermal regime in the ground and effects of heat from
susceptible over-burden, floor loading is high, and gravel
facilities have been discussed in general terms in
is available, the silt should be removed and replaced with
paragraphs 1-2 and 2-1. Beneath and surrounding a
gravel, and a slab-on-grade type foundation should be
foundation on frozen soil, the degree of disturbance of
employed. For a facility in which a more modest floor
the normal thermal regime brought about by construction
load capacity would be acceptable, a basement-type
depends upon such factors as construction methods,
construction might be considered since this would avoid
exposure, drainage, snow cover and drifting, and extent
the hauling, spreading and compaction of gravel.
of disturbance or change of the original surface cover, in
However, a basement water problem might be
addition to normal heat loss from the structure which
encountered if thaw water were unable to drain naturally
may reach the ground. These factors must be taken into
from the thaw bulb which will develop under the
account in estimating both the immediate and long term
structure.
stability of the struc-
4-6
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