U.S. patent number 3,791,443 [Application Number 05/207,379] was granted by the patent office on 1974-02-12 for foundation for construction on frozen substrata.
This patent grant is currently assigned to Atlantic Richfield Company. Invention is credited to Glenn R. Burt, Albert C. Condo, Kay E. Eliason, Richard L. Odsather.
United States Patent |
3,791,443 |
Burt , et al. |
February 12, 1974 |
FOUNDATION FOR CONSTRUCTION ON FROZEN SUBSTRATA
Abstract
A foundation construction, particularly useful for buildings and
other supported structures in Arctic regions wherein a permafrost
condition typically prevails, is provided by a construction pad
having at least one or more perforated and ventilated conduits
positioned within a cushion of air-permeable particulate material,
said cushion containing the perforated conduit being substantially
thermally isolated from the supported structure by means such as
encapsulating with an insulating material. Generally, the pad is
overburdened with, or imbedded in, a suitable gravel fill material.
The pad can substantially reduce, and in certain instances
eliminate, the necessity of providing piling supports in Arctic
regions and furthermore provides both a thermal barrier restricting
heat flowing downward from the building to the frozen substrata and
a type of thermal shunt blocking heat from the structure while
admitting a certain amount of geothermal heat flowing upward from
the ground to an ambient air heat sink.
Inventors: |
Burt; Glenn R. (Deer Park,
TX), Condo; Albert C. (Newtown Square, PA), Odsather;
Richard L. (Fairbanks, AK), Eliason; Kay E. (Fort
Madison, IA) |
Assignee: |
Atlantic Richfield Company (New
York, NY)
|
Family
ID: |
22770301 |
Appl.
No.: |
05/207,379 |
Filed: |
December 13, 1971 |
Current U.S.
Class: |
165/45; 52/169.5;
166/901; 405/229; 52/169.11; 62/260; 405/131; 454/251 |
Current CPC
Class: |
E02D
3/115 (20130101); E02D 27/35 (20130101); Y10S
166/901 (20130101) |
Current International
Class: |
E02D
3/115 (20060101); E02D 27/35 (20060101); E02D
3/00 (20060101); E02D 27/32 (20060101); E02d
003/00 () |
Field of
Search: |
;165/45 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
767,887 |
|
Sep 1967 |
|
CA |
|
248,161 |
|
Jan 1948 |
|
CH |
|
Other References
Arctic Construction: Buildings and Utilities, Prepared at the U.S.
Army Engineer School, CN-C.022-12, Oct. 1961..
|
Primary Examiner: Davis, Jr.; Albert W.
Assistant Examiner: Richter; S. J.
Attorney, Agent or Firm: Reap; Coleman R.
Claims
We claim:
1. A thermal barrier capable of being employed in Arctic region
construction comprising at least one perforated and ventilated
conduit positioned within a cushion of air-permeable load-bearing
particulate material wherein said particulate material is
substantially completely encapsulated with synthetic insulating
load-bearing material from ambient environment.
2. The thermal barrier of claim 1 wherein said conduit is at least
one pair of air conduits arranged to provide an air inlet conduit
and a separate air outlet conduit.
3. The thermal barrier of claim 1 wherein said insulating material
is a synthetic polymeric foam.
4. The thermal barrier of claim 3 wherein said synthetic polymeric
foam is a polyurethane.
5. The thermal barrier of claim 1 having means to provide
evaporative cooling within the thermal barrier.
6. The thermal barrier of claim 5 wherein evaporation cooling is
provided by a water spray system at the air inlet of the
conduit.
7. A foundation construction, useful in Arctic regions wherein a
permafrost condition typically pervails, capable of providing a
thermal barrier between a structure and the substrata comprising a
pad having at least one perforated and ventilated conduit
positioned within a cushion of air-permeable particulate material,
said cushion and perforated conduit being substantially completely
encapsulated by synthetic insulating material.
8. A foundation construction according to claim 7 wherein said pad
is encapsulated with a foamed polyurethane insulating material.
9. A foundation construction according to claim 7 wherein said
structure is a building.
10. A foundation construction according to claim 7 wherein said
substrata is a frozen substrata.
11. A foundation construction according to claim 7 having
mechanical means for forcing air through the perforated
conduits.
12. A foundation construction according to claim 7 wherein said
insulation material is synthetic foam.
13. A foundation construction according to claim 12 wherein said
synthetic foam is selected from the group consisting of
polyurethanes and polystyrenes.
14. A foundation construction according to claim 7 wherein said
perforated conduit is a series of conduits independently spaced and
distributed within the cushion of particulate material.
15. A foundation construction according to claim 14 wherein said
series of conduits comprise at least one communicating pair of
inlet and outlet conduits.
16. In a building structure for northern regions having a building
supported on a foundation, the improvement wherein a pad is
positioned beneath the building floor, said pad being substantially
completely thermally isolated from the ambient environment and
having at least one perforated and ventilated conduit placed within
a cushion of air-permeable particulate material said cushion being
encapsulated in synthetic insulating material.
17. The building structure according to claim 16 wherein said
conduit comprises at least one communicating pair of inlet and
outlet conduits.
18. A method of thermally insulating a frozen substrata from a
structure located above said frozen substrata comprising installing
beneath the structure a pad of air permeable particulate material
having at least one perforated conduit positioned therein,
encapsulating said pad with a thermal insulating material and
intermittently forcing air through said conduit.
19. A method according to claim 18 wherein said thermal insulating
material is a synthetic foam selected from group consisting of
polyurethanes and polystyrenes.
Description
BACKGROUND OF THE INVENTION
Regions of the Arctic and sub-Arctic wherein perpetually frozen
ground starts a few feet below the surface and extends downwardly
are generally referred to as permafrost regions. Permafrost is
permanently frozen ground and consists of mixtures of varying
content of water, salt, sand and gravel. At the ground surface
there is an active growth layer called the tundra which covers the
permafrost and in the spring and summer thawing occurs to varying
depths ranging from a few inches to several feet in an area between
the tundra mat and permafrost zone which is called the "active
layer." Thaw converts the tundra and active layer into a soggy
marsh having minimal load bearing value. Thus, any foundation will
displace the mud causing the building structure to either sink or
become unstable.
Generally, foundations for such building structures as well as
storage tanks, boiler houses and power plants are supported on the
permafrost by pilings of steel or timber. The pilings are necessary
to avoid excessive settlement caused by repeated thawing and
subsequent subsidence of the Arctic substrata. However,
installation of pilings not only requires a substantial investment
but pilings may not adequately protect the building from the
vagaries of the active layer such as frost-heave or "pole-jacking"
due to freezing and thawing. Therefore, a more economical and
efficient method for constructing building foundations would be an
important contribution to the technology of coping with the climate
variations of northern regions where a permafrost condition
prevails.
It is known in the building of structures in permafrost regions
that the foundation of the structures may be laid on gravel pads or
sills. However, a gravel pad tends to function as too good a
thermal conductor by permitting heat from the building floor to
reach the permafrost substrata and conversely the temperature of
the permafrost will be conducted upwardly toward that of the
building floor. Therefore, a gravel pad, by itself, fails to
completely eliminate the cycle of heaving and settlement resulting
from seasonal freezing and thawing and subsidence due to permafrost
destruction.
It is also known to place an insulating layer at some point between
the building floor and the permafrost substrata; however, an
insulating layer does not permit selective temperature control at
the insulating layer environment such as to impede heat-input to
the frozen substrata. Furthermore, an insulating layer functioning
as the sole thermal barrier would be of substantial thickness and
therefore economically expensive to install as well as be
technically unsuitable. Likewise, other high thermal impedance
systems such as gravel are similarly disadvantageous.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a foundation
construction particularly useful as a foundation for building
structures in northern regions wherein a permafrost condition
typically prevails. It is another object of this invention to
provide a method of constructing a building foundation that will
substantially reduce or eliminate the necessity of placing
buildings on pilings. It is still another object of this invention
to provide a foundation construction having a thermal barrier
between the structure and the frozen substrata restricting heat
flowing downward from the structure to the frozen substrata and
providing a thermal shunt blocking heat from the structure while
admitting some geothermal heat flowing upward from the permafrost
substrata to an ambient air heat sink. A still further object of
the invention is to provide an efficient and simplified thermal
barrier that may be employed in construction in northern regions
such as the Arctic and sub-Arctic
These and other objects of the invention are accomplished by
providing a thermal barrier between the structure and the substrata
comprising at least one perforated and ventilated conduit
positioned within a cushion of air-permeable particulate material,
said cushion and perforated conduit being substantially thermally
isolated from the ambient atmosphere by encapsulation within an
insulation material. If desired, the conduit system may comprise
communicating pairs of inlet and outlet conduits.
DESCRIPTION OF THE INVENTION
The advantages of the invention will become more apparent from the
following description considered in conjunction with the
accompanying drawings wherein:
FIG. 1 is a cross section view of the foundation construction
illustrating one embodiment of the invention;
FIG. 2 is a plan view of one variation of conduit arrangement
within the cushion of particulate material;
FIG. 3 is another plan view illustrating the communicating pair
arrangement of the conduits within the cushion of particulate
material;
FIG. 4 is a fragmentary cross section view of a second embodiment
of the foundation construction in accordance with the present
invention;
FIG. 5 is a fragmentary cross section view of a third embodiment of
the foundation construction in accordance with the present
invention; and
FIG. 6 is another fragmentary cross section view of a fourth
embodiment of the foundation construction.
Before giving detailed descriptions of the various views of the
drawings, briefly stated in the foundation construction of the
present invention requires a barrier that is thermally isolated
from ambient air being, generally, in the form of a pad containing
a perforated and ventilated conduit system embedded in a cushion of
air-permeable particulate material wherein the perimeter of the pad
is isolated from ambient air by encapsulation. Generally, the
ventilated and perforated conduit system draws air from an inlet
source through the conduits by mechanical means such as an exhaust
fan to an outlet point while the perforations permit air within the
thermally isolated cushion of air-permeable particulate material to
also be drawn to the conduit outlet.
The perforated and ventilated conduit system is an essential
feature of the invention and provides the means to move air within
the air-permeable particulate material. For instance, during colder
periods, ventilating means such as an exhaust fan placed at the
outlet point of the conduit can be operated to draw cold ambient
air through the particulate material and exhaust warm air
transferred from the building floor to the cushion of particulate
material. Therefore, the pad provides a means to intercept warm air
flowing from the building floor toward the frozen substrate and
dissipate it by conducting the air to the outer ambient "heat
sink." At times when the ambient air is warmer than the desired
temperature within the pad, the system may be shut down. Therefore,
the pad functions in a different manner than mere insulation
material that is incapable of dissipating heat but only serves to
retard its passage to some degree.
Another essential feature of the invention is to provide means of
thermal isolation of the pad from the ambient atmosphere in order
to permit the pad to function as a thermal barrier so that
temperatures within the pad are controllable. The pad may be
thermally isolated by such means as encapsulation with an
insulating material or by combinations of encapsulating means
utilizing insulating material, gravel, sand, the building itself,
frozen substrata, or other suitable barrier materials as will be
described in greater detail hereinafter.
Referring now in greater detail to the various views of the
drawings, in cross section view FIG. 1 thermally isolated pad 10
comprises perforated and ventilated conduits 12 horizontally spaced
and containing perforations 14 and wherein the conduits are
cushioned on screened particulate material 16. For purposes of this
invention the term "particulate material" designates air-permeable
granules in the form of discrete particles as opposed to a mass of
fines. Substantially all particles of air-permeable particulate
material will have a diameter greater than the diameter of the
perforations of the conduit to prevent clogging of the conduit with
particulate material. However, small amounts of fines may be
present in the particulate material to provide stability in the
cushion. Suitable particulate material include screened gravel,
crushed rock, pulverized concrete, and the like. The cushion of
air-permeable particulate material 16 and the perforated portions
of conduits 12 are encapsulated with insulation layer 18 to provide
thermal isolation from the ambient air. Those portions of the
conduit exposed to the ambient environment and/or are otherwise
outside of the thermal barrier are solid (i.e., not perforated).
Pad 10 is overburdened with granular fill material 20 that may be
any conventionally used fill of any desired particle size used for
base construction of buildings, roads, etc., such as gravel,
crushed rock, sand and the like.
Ventilators 28 and 30 are provided at the conduit extremities to
permit passage of air through the conduit. Motorized fans or blower
arrangements 32 pull air into inlet ventillator 28 and through
conduit 12 to exhaust ventilator 30. The fans or blowers may be
provided with temperature control means such as thermostat 34 to
actuate the blower arrangement whenever it is necessary to
dissipate heat build-up or otherwise alter the temperature within
the pad.
Pat 10 is positioned beneath building floor 24 and rests on frozen
substrata 22. Building floor 24 may be concrete, wood, metal or any
suitable flooring material and rests on the granular fill material
20. Building load bearing supports 26 may also be of any suitable
construction material as well as building walls 36.
Preferably, insulation layer 18 is a rigid synthetic foam
insulating material such as any of the polyurethanes or
polystyrenes capable of supporting a load in low temperature
applications without over-compressing or otherwise interfering with
the thermal insulation properties. The thickness of the insulating
pad may vary according to such parameters as the type of the
insulating material used, the building design, environmental
conditions, and the nature of the pad. Insulation thickness may be
calculated from known equations which consider such variables as
conductivity of the insulation, conductivity of the ground surface,
thermal history of ambient air and temperature of the ground
surface. Synthetic polymeric foams such as polyurethane
specifically designed for low temperature environments are
particularly desirable. However, other insulating means to provide
the thermal barrier such as conventional inorganic materials
including asbestos, fiberglass, insulating concrete block and the
like could be employed for a portion or all of the insulation
depending upon the building design and environmental
conditions.
FIGS. 2 and 3 are fragmentary views illustrating various placements
of the conduits within pad 10. In FIG. 2 conduits 12a, 12b, and 12c
are distributed at longitudinally spaced intervals 11 with each
conduit having an air intake 21a, 21b and 21c and an air exhaust
23a, 23b and 23c. However, if desired, all or a portion of the air
intakes may be connected to a common air intake and likewise all or
a portion of the air exhausts may be connected to a common air
exhaust. The particular longitudinal spacing 11 arrangement of the
conduits or a desired vertical spacing may depend upon the nature
of the particulate material, the size of the foundation, the
temperature within the building, properties of the insulation, as
well as other environmental considerations. Arrows A-1 through A-6
generally illustrate the air flow path within the thermally
isolated pad and particularly illustrate that the voids within the
particulate material permit air circulation within the thermally
isolated pad.
FIG. 3 is another fragmentary view of the thermally isolated pad
illustrating a conduit system wherein individual conduits are
employed for air intake and individual conduits employed for air
exhaust. Conduits 12u, 12v, 12w, 12x, 12y and 12z are
longitudinally spaced within the cushion of particulate material.
Conduits 12u, 12w, and 12y function as air intakes at 21d, 21e and
21f. Conduits 12v, 12x and 12z function as exhaust means at 23d,
23e, and 23f. For foundations of larger buildings the conduit
placement of FIG. 3 may be desirable to provide improved air
circulation within the thermally isolated pad. Although the FIG. 3
conduits illustrate a horizontal arrangement, the conduits may be
independently spaced vertically and horizontally within the
air-permeable particulate material. Arrows A-10 through A-16
generally indicate the air flow path within the pad. If desired,
the air intake points may be commoned as well as air exhaust
points.
FIGS. 4, 5, and 6 illustrate alternative means of providing the
thermal isolation for the pad. In FIG. 4 the fragmentary view
illustrates a system similar to FIG. 1 with the exception the
insulating layer between conduit 12 and frozen substrata 22 is
omitted. In this embodiment thermal isolation beneath the conduit
is provided by the combination of granular fill material and frozen
substrata. Suitable thermal isolation means are provided at the
sides of the pad and insulating layer 18 is a thermal barrier above
the pad.
FIG. 5 is similar to FIG. 4 but in this embodiment the separate
insulation material above the conduit was omitted so that the
insulating layer is provided by the building floor. Suitable
insulating means substantially enclose the sides of the pad.
FIG. 6 is similar to FIG. 1 with the exception that the granular
fill material was omitted so that the thermally isolated pad
provides the entire foundation beneath the building.
In a preferred embodiment of this invention, the foundation
construction is generally provided in the following manner. If the
pad will be substantially encapsulated with a synthetic foam
insulating material, a layer of insulation will be placed on the
ground surface occupied by the proposed pad and then a layer of
appropriate particulate material sufficient to support the conduit
system placed on the insulation. After determining the pattern of
placing the conduit system, i.e., to longitudinally and/or
vertically space or a combination of both, the conduit system is
laid and additional particulate material embeds the conduit system
to provide the cushion. Then the remainder of the pad may be
enclosed with insulation material to provide a thermal barrier
obtained by an encapsulated layer of insulation. Installation of
ventilating means such as motorized fans will pull the air from an
inlet source to an exhaust point. The pad may be overburdened with
appropriate granular fill material conventionally used as a base
for building foundations, roadways, etc.
For purposes of this invention the term "thermally isolated" means
that the cushion of air-permeable particulate material and
perforated conduits, together with any required barrier material,
create a thermal barrier so that substantially no significant
uncontrolled amount of ambient air is permitted to enter the
barrier, except that controlled amount entering the air intake
distribution system, unless so desired. Although thermal isolation
is generally obtained by an encapsulating layer of insulation
material, in some instances the building floor, frozen substrata,
etc., provide a portion of the thermal barrier. In addition to
synthetic foams, other inorganic insulating materials such as
insulated concrete block, insulating boards, etc., may be used, in
whole or in part, to provide a thermal barrier.
In instances wherein the insulating material possesses
water-absorbing properties, it is desirable to provide a
hydrophobic or water impermeable layer to the foundation substrate.
Generally, this hydrophobic barrier layer or "precoat" would be
applied while warm and thereafter a layer of polyurethane foam may
be spray applied to the warm surface. The thickness of the barrier
layer may be in the range of from about 5 mils to 30 mils.
If the particular insulating material is a synthetic polymeric film
such as a polyurethane, it is preferred to spray apply the foam in
layers of about 3 to 8 per inch. In applying successive
superimposed layers of foam to obtain cohesion between the layers,
time should be allowed for the formation of a skin so that it is
uniform and free from discontinuities before the next layer is
applied. In order to get chemical bonding and consequently greater
cohesion and strength, it is preferred to apply the next layer of
foam before the skin layer on the layer of foam below has
completely cured. In general, the next layer of foam should be
applied within 1/2 to 30 minutes after the layer below it has
completed foaming. This permits the lower skin layer to be
completely formed without being completely cured and at the same
time allows for variations in temperature.
In the construction of a warehouse building in the Prudhoe Bay area
of the Arctic on a frozen substrata wherein the area of the
building floor measures approximately 60 feet by 80 feet, a
foundation pad for the building is provided as follows: A
bituminous moisture barrier coating a petroleum residuum containing
polyethylene is applied to an area of approximately 65 feet by 85
feet and thereafter about 11/2 inches of a rigid polyurethane foam
designed for low temperature application is applied with a spray
foam machine using dichlorodifluoromethane as the blowing agent.
Generally, any lower layer of insulation will extend beyond the
building perimeter so that any thaw under the edge of the
insulation does not proceed too closely to the direct load of the
building. The foam has the following physical properties: A
thermoconductivity of 0.13 BTU/Hr./Ft..sup.2 /.degree.F./In. (k
factor at 77.degree. F. as determined by ASTM-D-2326-64T using the
probe method), a compression strength at yield of 43- 50 psi, and
an over-all density of 2.7 lbs./ft..sup.3 (as determined by
ASTM-D-1622-63).
Thereafter, Prudhoe Bay area gravel screened to remove particles of
a size smaller than about 1/16 inch is placed over the entire
foamed area to a depth of about 12 inches. Three aluminum
perforated conduits each having a diameter of 10 inches are
horizontally spaced from each other on the screened gravel. The
size of the perforations of the concrete conduit are about 1/16
inch or smaller and the amount of perforated surface area of the
conduit is about 5 percent. Thereafter, additional screened
particulate material is poured over the duct so that the crown of
the conduits are overburdened with about 12 inches of screened
gravel. Using the same spray foam machine and the same polyurethane
insulating material, a layer of foam about 2 to 4 inches in
thickness applied in successive superimposed layers of about 5 per
inch is placed over the entire exposed screened gravel surface on
the top and sides and, together with the previously applied lower
layer of foam, a thermal barrier is provided. Ventilators and
appropriate fans or blowers are installed together with an optional
fan control system such as a thermostat designed to actuate the
fans when the temperature inside the thermal barrier is warmer than
the outside ambient air. The thermal barrier pad is now covered
with about 1 foot of granular fill material to provide a complete
foundation without the necessity of pilings; however, piling may be
provided as supplemental foundation means at high load-bearing
areas.
During warmer months in the northern regions when the temperature
of the ambient air exceeds the temperature within the thermal
barrier, it may be desirable to provide a refrigeration effect. One
method of accomplishing this is by an atomizer water spray system
to provide evaporative cooling. Such a system 38 may be provided at
the air inlet of the conduit as shown in FIG. 1 and would function
to conduct water saturated air through the pad. Such air moving
through the conduit by forcing means such as an exhaust or blower
system produces evaporation of the atomized moisture and a
resulting refrigeration effect so that the temperature within the
encapsulated pad would be significantly below the inlet ambient air
temperature. When the ambient air temperature reaches a point where
it exceeds the desired temperature within the encapsulated pad, the
motorized exhaust or blower system will automatically shut off if a
thermostat is employed; however, the aforementioned atomizer water
spray system would provide additional cooling means to dissipate
heat from the thermal barrier pad.
As another alternative system to provide additional cooling within
the encapsulated pad during warmer periods, the entire conduit
system may be closed and connected to a heat exchanger unit to
provide further control of the temperature within the pad.
Although this invention may obviate the necessity of pilings, in
certain instances wherein the building load is concentrated at a
particular point(s), it may be desirable to supplement the
foundation construction of this invention with timber, concrete or
steel pilings.
The moisture barrier coating is generally a bituminous composition,
but other materials may be employed, such as plastic films and the
like that act to separate surface moisture from any applied
synthetic foams. Preferred as the moisture barrier is a crude oil
residuum that may be extended with a synthetic polymeric material
such as a low molecular weight polyethylene or styrene-butadiene
rubber.
The aforementioned conduit systems were described as being
independently horizontally spaced; however, depending upon the
height of the pad, it may be desirable to horizontally and
vertically space the conduits or employ one or more conduits
wherein each winds a tortuous path within the thermal barrier.
Similarly, branched pipeline systems may be designed. Fluid flow
metering systems have been established for branching pipeline
systems so that equal pressures and volumes can be controlled by
determining the intake opening from the initial distribution
system. Thus conduits located at increasing distances from the
source will receive the same pressure and volume as those nearest
the source.
Although the foundation construction of this invention is primarily
intended for structures such as buildings, it may also be employed,
either alone or together with pilings, as the foundation for drill
rigs, water storage facilities, fuel storage bladders, pipelines,
exposed storage areas, and the like.
Reasonable variations and modifications are possible within the
scope of this invention without departing from the spirit and scope
of the claims.
* * * * *