CA1337786C - Floating foundation system - Google Patents
Floating foundation systemInfo
- Publication number
- CA1337786C CA1337786C CA 592014 CA592014A CA1337786C CA 1337786 C CA1337786 C CA 1337786C CA 592014 CA592014 CA 592014 CA 592014 A CA592014 A CA 592014A CA 1337786 C CA1337786 C CA 1337786C
- Authority
- CA
- Canada
- Prior art keywords
- frame
- foundation
- flotation
- flotation modules
- modules
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Landscapes
- Buildings Adapted To Withstand Abnormal External Influences (AREA)
Abstract
A floating foundation for use in discontinuous permafrost or areas of unstable soil conditions, comprising a substantially horizontal frame for carrying a structure having a predetermined bearing load, a plurality of flotation modules, and a plurality of pivotal connections between respective areas of the flotation modules and the frame. The flotation modules are connected in a distributed arrangement for maintaining the frame and supported structure supported on the discontinuous permafrost in a substantially horizontal plane.
Description
FLOATING FOUNDATION SYSTEM
Field of the Invention This invention relates in general to foundations, and more particularly to a floating foundation module for use in discontinuous permafrost or in areas having unstable soil conditions.
Background of the Invention Regions of discontinuous permafrost such as found in far Northern settlements, are typically characterized by an upper layer of 2-3', in depth that thaws in the summer and freezes in the winter, and a lower layer that is permanently frozen.
Buildings that are erected on discontinuous permafrost are commonly built on foundations of stacked lengths of 8" x 8" timber, one or more levels of timber being in an excavation in the aforementioned upper layer and the remainder being above grade. Such buildings are subjected to substantial settlement and movement during annual temperature and precipitation variations, and the life of such buildings is substantially less than that of buildings erected in more temperate climates.
One prior art approach to overcoming the problem of erecting structures on unstable soils is disclosed in U.S. patent 3,626,702 (Monahan). The prior art patent discloses a flotation method involving back filling of synthetic polymeric foams into a large excavation for providing a sub-foundation. A second rigid layer of concrete is then deposited on the floating sub-foundation, and the dwelling or other structure is erected on the second layer.
The system disclosed in the Monahan patent is system very useful in marshlands for providing a stable foundation platform on unstable sub-soil below the level of the surrounding water table. The buoyant nature of ~ 1 3377~6 the back-fill results in flotation which allows for the construction of structures of greater weight and height on a given area of land than was before possible.
However, the floating foundation of Monahan suffers from the same problQms as the first mention prior art buildings when construc~ed on discontinuous permafrost. In particular the sub-foundation of foam is subjected to substantial heaving and movement during successive freezing and thawing seasons. Furthermore, the continuous sub-foundati~n of foam in the Monahan system is subjected to ice lensing whereby the foam closest to the perimeter of the dwelling thaws first while the sub-foundation under the center of the building remains frozen. This results in excessive heaving of the sub-foundation and consequent cracking or damage to the overlying layer of concrete.
In accordance wit~ the present invention the prior art problems of settl~ment and movement are overcome by provision of a foundation comprising multiple floatation modules connected to a frame that floats the building during the time of the year when the upper layer is soft and unfrozen. Each flotation module is preferably connected to the network via a pivoted resilient support for accomnodating soil movement due to ice lensing, etc.
SummarY of the Invention In accordance with an aspect of the present invention there is provided a foundation supporting a structure on land which is ~;usceptible to the formation of discontinuous permafrost, wherein the structure is characterized by a predetermined bearing load. The foundation comprises a substantially horizontal frame carrying the structure, a plurality of flotation modules resting on the land which is susceptible to formation of discontinuous permafrost, and a plurality of resilient pivotal joints connecting respective ones of the flotation modules to the frame in a distributed ~ .
arrangement, for maintaining the frame and the structure supported on the land which is susceptible to discontinuous permafrost in a substantially horizontal plane.
Description of the Drawings A preferred embodiment of the present invention will be described in detail below with reference to the following drawings, in which:
Figure 1 is a perSpective view of a single story family dwelling supported by a floating foundation in accordance with the pres~nt invention;
Figure 2 is a perspective view of a frame for the floating foundation of Figure 1;
Figure 3 is a plan view of the frame shown in Figure 2 with a plurality of flotation modules connected thereto;
Figure 4 is a perspective view of a flotation module in accordance with a preferred embodiment of the present invention; and Figure 5 is a perspective view of a flotation module having a modified pi~otal connection in accordance with an alternative embodiment of the present invention.
Detailed Description of the Invention Turning to Figure 1, a standard single story family dwelling 1 is shown ~ounted on a frame 3 supported by a plurality of flotation modules 10 pivotally connected to the frame 3.
The floating foundation rests on the surface of the active layer of discontinuous permafrost requiring only a rough levelling of the active layer. This eliminates any requirement for excavation or heavy ~i equipment and also prevents the destruction of natural drainage patterns.
A unique property of the floating foundation comprising frame 3 and flotation modules 10 is the ability to support the load of the structure or dwelling although the bearing capacity of the active layer of permafrost may be reduced significantly during seasonal thawing cycles. Differential settlement, frost heave and racking are completely avoided since the floating structure is able to sustain constant and adequate structural support by distributing the load and self-adjusting to vertical displacements resulting from seasonal thawing and freezing cycles.
With reference to Figure 2, the frame 3 comprises of a pair of parallel double ply header beams 12 each preferably comprising 1 3/4" x 14" x 36' boards and six 24' three ply spanning beams 14, each ply preferably comprising 1 3/4" x 14" x 24' boards.
To match the frame design and provide an equal loading pattern, a twelve point support system is used for connecting the flotation modules 10, as shown in Figure 3.
The flotation modules 10 are connected at the twelve points along respective joints between header beams 12 and spanning beams 14. Thus, the frame 3 carries the dwelling 1 (Figure 1) without any central supports, thereby avoiding the consequences of differential thawing patterns and ensuring that each flotation module 10 is easily accessible for servicing or inspection.
The loads for a typical Northern housing unit measuring 26' x 24' and located in the discontinuous permafrost zone, are as follows:
Dead load = 20 psf Live load = 40 psf Snow load = 36 pst Total = 96 psf (approximately 100 psf) Therefore, the design load of the structure is = 100 psf x 36 foot x 24 foot = 86,400 lbs.
Number of support points = 12 Therefore, the loading per support point = 7,200 lbs.
The bearing capacity of soft clay has a maximum allowable pressure of 835 lbs. per square foot, (National Building Code). However, with the introduction of water during the thawing process this can be greatly reduced. Assuming that 60% of the allowable bearing capacity is lost due to water, the active layer of discontinuous permafrost would be characterized by a bearing capacity of approximately 335 lbs. per square foot.
Therefore, the size of each flotation module should be 7,200 lbs./335 lbs. per square foot = 21.5 square feet.
With reference to Figure 4, the flotation module 10 is shown in greater detail comprising a float pad frame 16 comprising a plurality of preferably 2' x 6' planks 17 connected via brackets in a straightforward manner. Four foam filled flotation elements 18 are connected to predetermined ones of planks 17 on the underside of the frame 16 via mechanical fastening such as washer and lag screw, strapping, etc.
The float plank frame 16 operates to transfer the bearing load from the house frame 3 to the floats 18.
Each flotation element 18 is preferable in the form of blow molded or rotary molded polymer block foamed in place with polystyrene to provide buoyancy.
Other buoyant materials could be used in place of ~ 6 1 337786 polystyrene, e.g. urethane, and it also would be possible to employ a hollow housing filled with air.
The latter is not preferred, however, since it could be punctured as a result of vandalism or through an accident resulting in a loss of buoyancy for the housing.
According to the successful prototype of the invention, the four floats or flotation elements 18 on each module 10 provide a surface area of 24' x 24' which is more than the aforementioned required 21.5 square feet for the standard Northern housing design.
Furthermore, the floats 18 provide an additional uplift force due to buoyancy of up to approximately 430 lbs.
per float. Thus, the preferred four floats or floating elements 18 per module 10 provide adequate support with a significant safety margin.
A central reinforced portion 20 of the pad frame 16 has a resilient pivotal connection 22 mounted thereon. According to the preferred embodiment, the pivotal connection 22 comprises a pivot joint biased by a compression spring. The spring consists of a 1-1/8 bar stock material which is capable of supporting 7,200 lbs. at full compression and a change in vertical displacement of approximately 3.5".
An elastomeric hinge 24 is connected by a corresponding bracket to each of the four outside corners of the pad frame 16 for inter-connecting adjacent ones of the 14 flotation modules 10.
The elastomeric hinges 24 allow each individual flotation module 10 to move vertically for adjusting to seasonal soil conditions. The hinges 24 also allow for distribution of the bearing load among successive ones of the modules 10. At the same time, the hinges 24 inhibit the float pad frame 16 from moving horizontally.
Turning briefly to Figure 5, an alternative embodiment of the pivotal connection 33 is shown comprising a compressible columnar enclosure 32 filled with one of either hydraulic fluid or air, and a pair of hydraulic coupling tubes 34 for inter-connecting respective enclosures 32 on adjacent modules lO.
In operation, upon compression under load of a predetermined one of the enclosures 32, hydraulic fluid or air passes via couplings 34 to adjacent modules lO
thereby permitting vertical deflection of individual ones of the modules lO while maintaining even load distribution throughout the foundation. It is contemplated that the hydraulic fluid may be selected so as to freeze during the cold season for maintaining a rigid foundation until spring thaw begins.
In summary, the floating foundation of the present invention is characterized by the advantages of low cost construction, small and lightweight components requiring limited air transport and easy assembly using common carpentry tools. The load on each module lO is distributed equally for avoiding uneven settlement during spring thawing of discontinuous permafrost.
Central supports under the middle of the housing units are eliminated for avoiding differential thawing patterns (e.g. ice lensing) and to ensure that each module is accessible for inspection or servicing.
Furthermore, the floating foundation of the present invention may be installed with minimal excavation, thereby avoiding the requirement for heavy equipment as well as preserving natural drainage patterns.
Other embodiments or variations are possible without departing from the sphere and scope of the present invention as defined by the claims appended hereto.
Field of the Invention This invention relates in general to foundations, and more particularly to a floating foundation module for use in discontinuous permafrost or in areas having unstable soil conditions.
Background of the Invention Regions of discontinuous permafrost such as found in far Northern settlements, are typically characterized by an upper layer of 2-3', in depth that thaws in the summer and freezes in the winter, and a lower layer that is permanently frozen.
Buildings that are erected on discontinuous permafrost are commonly built on foundations of stacked lengths of 8" x 8" timber, one or more levels of timber being in an excavation in the aforementioned upper layer and the remainder being above grade. Such buildings are subjected to substantial settlement and movement during annual temperature and precipitation variations, and the life of such buildings is substantially less than that of buildings erected in more temperate climates.
One prior art approach to overcoming the problem of erecting structures on unstable soils is disclosed in U.S. patent 3,626,702 (Monahan). The prior art patent discloses a flotation method involving back filling of synthetic polymeric foams into a large excavation for providing a sub-foundation. A second rigid layer of concrete is then deposited on the floating sub-foundation, and the dwelling or other structure is erected on the second layer.
The system disclosed in the Monahan patent is system very useful in marshlands for providing a stable foundation platform on unstable sub-soil below the level of the surrounding water table. The buoyant nature of ~ 1 3377~6 the back-fill results in flotation which allows for the construction of structures of greater weight and height on a given area of land than was before possible.
However, the floating foundation of Monahan suffers from the same problQms as the first mention prior art buildings when construc~ed on discontinuous permafrost. In particular the sub-foundation of foam is subjected to substantial heaving and movement during successive freezing and thawing seasons. Furthermore, the continuous sub-foundati~n of foam in the Monahan system is subjected to ice lensing whereby the foam closest to the perimeter of the dwelling thaws first while the sub-foundation under the center of the building remains frozen. This results in excessive heaving of the sub-foundation and consequent cracking or damage to the overlying layer of concrete.
In accordance wit~ the present invention the prior art problems of settl~ment and movement are overcome by provision of a foundation comprising multiple floatation modules connected to a frame that floats the building during the time of the year when the upper layer is soft and unfrozen. Each flotation module is preferably connected to the network via a pivoted resilient support for accomnodating soil movement due to ice lensing, etc.
SummarY of the Invention In accordance with an aspect of the present invention there is provided a foundation supporting a structure on land which is ~;usceptible to the formation of discontinuous permafrost, wherein the structure is characterized by a predetermined bearing load. The foundation comprises a substantially horizontal frame carrying the structure, a plurality of flotation modules resting on the land which is susceptible to formation of discontinuous permafrost, and a plurality of resilient pivotal joints connecting respective ones of the flotation modules to the frame in a distributed ~ .
arrangement, for maintaining the frame and the structure supported on the land which is susceptible to discontinuous permafrost in a substantially horizontal plane.
Description of the Drawings A preferred embodiment of the present invention will be described in detail below with reference to the following drawings, in which:
Figure 1 is a perSpective view of a single story family dwelling supported by a floating foundation in accordance with the pres~nt invention;
Figure 2 is a perspective view of a frame for the floating foundation of Figure 1;
Figure 3 is a plan view of the frame shown in Figure 2 with a plurality of flotation modules connected thereto;
Figure 4 is a perspective view of a flotation module in accordance with a preferred embodiment of the present invention; and Figure 5 is a perspective view of a flotation module having a modified pi~otal connection in accordance with an alternative embodiment of the present invention.
Detailed Description of the Invention Turning to Figure 1, a standard single story family dwelling 1 is shown ~ounted on a frame 3 supported by a plurality of flotation modules 10 pivotally connected to the frame 3.
The floating foundation rests on the surface of the active layer of discontinuous permafrost requiring only a rough levelling of the active layer. This eliminates any requirement for excavation or heavy ~i equipment and also prevents the destruction of natural drainage patterns.
A unique property of the floating foundation comprising frame 3 and flotation modules 10 is the ability to support the load of the structure or dwelling although the bearing capacity of the active layer of permafrost may be reduced significantly during seasonal thawing cycles. Differential settlement, frost heave and racking are completely avoided since the floating structure is able to sustain constant and adequate structural support by distributing the load and self-adjusting to vertical displacements resulting from seasonal thawing and freezing cycles.
With reference to Figure 2, the frame 3 comprises of a pair of parallel double ply header beams 12 each preferably comprising 1 3/4" x 14" x 36' boards and six 24' three ply spanning beams 14, each ply preferably comprising 1 3/4" x 14" x 24' boards.
To match the frame design and provide an equal loading pattern, a twelve point support system is used for connecting the flotation modules 10, as shown in Figure 3.
The flotation modules 10 are connected at the twelve points along respective joints between header beams 12 and spanning beams 14. Thus, the frame 3 carries the dwelling 1 (Figure 1) without any central supports, thereby avoiding the consequences of differential thawing patterns and ensuring that each flotation module 10 is easily accessible for servicing or inspection.
The loads for a typical Northern housing unit measuring 26' x 24' and located in the discontinuous permafrost zone, are as follows:
Dead load = 20 psf Live load = 40 psf Snow load = 36 pst Total = 96 psf (approximately 100 psf) Therefore, the design load of the structure is = 100 psf x 36 foot x 24 foot = 86,400 lbs.
Number of support points = 12 Therefore, the loading per support point = 7,200 lbs.
The bearing capacity of soft clay has a maximum allowable pressure of 835 lbs. per square foot, (National Building Code). However, with the introduction of water during the thawing process this can be greatly reduced. Assuming that 60% of the allowable bearing capacity is lost due to water, the active layer of discontinuous permafrost would be characterized by a bearing capacity of approximately 335 lbs. per square foot.
Therefore, the size of each flotation module should be 7,200 lbs./335 lbs. per square foot = 21.5 square feet.
With reference to Figure 4, the flotation module 10 is shown in greater detail comprising a float pad frame 16 comprising a plurality of preferably 2' x 6' planks 17 connected via brackets in a straightforward manner. Four foam filled flotation elements 18 are connected to predetermined ones of planks 17 on the underside of the frame 16 via mechanical fastening such as washer and lag screw, strapping, etc.
The float plank frame 16 operates to transfer the bearing load from the house frame 3 to the floats 18.
Each flotation element 18 is preferable in the form of blow molded or rotary molded polymer block foamed in place with polystyrene to provide buoyancy.
Other buoyant materials could be used in place of ~ 6 1 337786 polystyrene, e.g. urethane, and it also would be possible to employ a hollow housing filled with air.
The latter is not preferred, however, since it could be punctured as a result of vandalism or through an accident resulting in a loss of buoyancy for the housing.
According to the successful prototype of the invention, the four floats or flotation elements 18 on each module 10 provide a surface area of 24' x 24' which is more than the aforementioned required 21.5 square feet for the standard Northern housing design.
Furthermore, the floats 18 provide an additional uplift force due to buoyancy of up to approximately 430 lbs.
per float. Thus, the preferred four floats or floating elements 18 per module 10 provide adequate support with a significant safety margin.
A central reinforced portion 20 of the pad frame 16 has a resilient pivotal connection 22 mounted thereon. According to the preferred embodiment, the pivotal connection 22 comprises a pivot joint biased by a compression spring. The spring consists of a 1-1/8 bar stock material which is capable of supporting 7,200 lbs. at full compression and a change in vertical displacement of approximately 3.5".
An elastomeric hinge 24 is connected by a corresponding bracket to each of the four outside corners of the pad frame 16 for inter-connecting adjacent ones of the 14 flotation modules 10.
The elastomeric hinges 24 allow each individual flotation module 10 to move vertically for adjusting to seasonal soil conditions. The hinges 24 also allow for distribution of the bearing load among successive ones of the modules 10. At the same time, the hinges 24 inhibit the float pad frame 16 from moving horizontally.
Turning briefly to Figure 5, an alternative embodiment of the pivotal connection 33 is shown comprising a compressible columnar enclosure 32 filled with one of either hydraulic fluid or air, and a pair of hydraulic coupling tubes 34 for inter-connecting respective enclosures 32 on adjacent modules lO.
In operation, upon compression under load of a predetermined one of the enclosures 32, hydraulic fluid or air passes via couplings 34 to adjacent modules lO
thereby permitting vertical deflection of individual ones of the modules lO while maintaining even load distribution throughout the foundation. It is contemplated that the hydraulic fluid may be selected so as to freeze during the cold season for maintaining a rigid foundation until spring thaw begins.
In summary, the floating foundation of the present invention is characterized by the advantages of low cost construction, small and lightweight components requiring limited air transport and easy assembly using common carpentry tools. The load on each module lO is distributed equally for avoiding uneven settlement during spring thawing of discontinuous permafrost.
Central supports under the middle of the housing units are eliminated for avoiding differential thawing patterns (e.g. ice lensing) and to ensure that each module is accessible for inspection or servicing.
Furthermore, the floating foundation of the present invention may be installed with minimal excavation, thereby avoiding the requirement for heavy equipment as well as preserving natural drainage patterns.
Other embodiments or variations are possible without departing from the sphere and scope of the present invention as defined by the claims appended hereto.
Claims (7)
1. A foundation supporting a structure on land which is susceptible to the formation of discontinuous permafrost, said structure being characterized by a predetermined bearing load, comprising:
a) a substantially horizontal frame carrying said structure;
b) a plurality of flotation modules resting on said land which is susceptible to formation of discontinuous permafrost; and c) a plurality of resilient pivotal joints connecting respective ones of said flotation modules to said frame in a distributed arrangement for maintaining said frame and said structure supported on said land which is susceptible to formation of discontinuous permafrost in a substantially horizontal plane.
a) a substantially horizontal frame carrying said structure;
b) a plurality of flotation modules resting on said land which is susceptible to formation of discontinuous permafrost; and c) a plurality of resilient pivotal joints connecting respective ones of said flotation modules to said frame in a distributed arrangement for maintaining said frame and said structure supported on said land which is susceptible to formation of discontinuous permafrost in a substantially horizontal plane.
2. A foundation as defined in claim 1, further comprising means for hinging together adjacent ones of said flotation modules to allow vertical movement of said flotation modules responsive to seasonal changes in said discontinuous permafrost while preventing horizontal movement of said flotation nodules.
3. A floating foundation as defined in claim 1, wherein said plurality of flotation modules are connected to said frame along a pair of outside edges thereof, such that the frame is carried without central supports for avoiding frost heaving and settlement due to differential thawing patterns.
4. A foundation as defined in claim 1, 2, or 3, wherein said frame further comprises a pair of parallel double-ply header beams and a plurality of three-ply spanning beams connected orthogonally at each end to respective ones of said header beams.
5. A foundation as defined in claim 1, 2 or 3, wherein each said plurality of flotation modules comprises a float pad frame and a plurality of foam filled floats connected to said float pad frame.
6. A floating foundation as defined in claim 1, 2 or 3, wherein each said plurality of means for pivotally connecting comprises a support for direct connection to said frame and pivoted connection to a predetermined one of said flotation modules, and a coil spring for accommodating vertical displacement between said frame and said predetermined one of said flotation modules.
7. A floating foundation as defined in claim 1, 2 or 3, wherein said plurality of means for pivotally connecting comprise a plurality of compressible columnar enclosures connected to said frame and respective ones of said flotation modules, each said enclosures being filled with one of either hydraulic fluid or air, and a plurality of couplings between adjacent ones of said enclosures for conveying said one of either hydraulic fluid or air therebetween responsive to periodic compression and expansion of said enclosures.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB888804550A GB8804550D0 (en) | 1988-02-26 | 1988-02-26 | Floating foundation system |
| GB8,804,550 | 1988-02-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1337786C true CA1337786C (en) | 1995-12-26 |
Family
ID=10632439
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 592014 Expired - Fee Related CA1337786C (en) | 1988-02-26 | 1989-02-24 | Floating foundation system |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1337786C (en) |
| GB (1) | GB8804550D0 (en) |
-
1988
- 1988-02-26 GB GB888804550A patent/GB8804550D0/en active Pending
-
1989
- 1989-02-24 CA CA 592014 patent/CA1337786C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| GB8804550D0 (en) | 1988-03-30 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |