CA1045837A - Method and structural support for increasing load-carrying capacity in permafrost - Google Patents
Method and structural support for increasing load-carrying capacity in permafrostInfo
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- CA1045837A CA1045837A CA300,620A CA300620A CA1045837A CA 1045837 A CA1045837 A CA 1045837A CA 300620 A CA300620 A CA 300620A CA 1045837 A CA1045837 A CA 1045837A
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- pile
- sleeve
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Abstract
ABSTRACT OF THE DISCLOSURE
A stepped pile unit for use in soil having a seasonally frozen region and a permanently frozen region, comprising at least one pile body having an upper end located in said seasonally frozen region and extending above the ground and a lower end extending into said permanently frozen region, elongated sleeve means encircling at least part of said upper end and extending downwardly along said lower end into said permanently frozen region, and means for struc-turally interconnecting the sleeve means and pile body and spacing said sleeve means radially outwardly of said pile body to increase the effective diameter of the pile body down into the permanently frozen region.
A stepped pile unit for use in soil having a seasonally frozen region and a permanently frozen region, comprising at least one pile body having an upper end located in said seasonally frozen region and extending above the ground and a lower end extending into said permanently frozen region, elongated sleeve means encircling at least part of said upper end and extending downwardly along said lower end into said permanently frozen region, and means for struc-turally interconnecting the sleeve means and pile body and spacing said sleeve means radially outwardly of said pile body to increase the effective diameter of the pile body down into the permanently frozen region.
Description
BACKGROUND OF THE_INVENT ON
Field of the Invention This invention pertains to methods and apparatuses for increasing the vertical and, more importantly, the lateral load-carrying capacity of a pile or pile-like supports in soil having an upper, seasonally frozen region and a lower, permanently frozen region. The invention is especially useful with refrigerating-type thermal piles which have the capability of removing heat from the permanently frozen region of the soil to increase the load-carrying capacity of the surrounding soil.
DescriPtion of the Prior Art Thermal piles for use in increasing load-carrying capacity have been used heretofore. One such pile is described in my earlier United States patent, No. 3,217,791. The lowering of the temperature of the permanently frozen region of permafrost soil increases the vertical and lateral load-carrying capacity of the soil surrounding the pile.
The common technique for meeting the load-carrying capacity of the piles used in a large building is to increase the size or diameter of the piles at the numerous locations around the building. It is expensive to manufacture and transport large thermal piles due to their weight and size. It is also expensive due to the fact that a thermal pile unit is essentially a pressure vessel which must be manufactured according to strict specifications. Large pressure vessels are extremely expensive. The lateral load-carrying capacity of a large-diameter pile is frequently less than is required for a pile designed to have a certain vertical load-carrying capacity~ Consequently, large piles are either over-designed, with excess vertical load-carrying capacity, or cross-bracing between piles in holes spaced around the building is provided between adjacent piles to obtain the necessary lateral load-carrying capacity. Both solutions, however, are expensive.
Stepped piles, having larger diameters at their upper ends than at their lower ends, are known. A stepped pile is useful in permafrost having a lower, permanently frozen region since the larger stepped diameter can be terminated below the upper surface of the permanently frozen region and not extend the full length of the pile without substantially reducing the lateral load-carrying capacity of the pile. By stepping the pile, the remaining !ower ~,~ .
-1- ~F '' portion of the pile can be built of considerably less material, providing a sub-stantial cost savings. The reason for this characteristic of a stepped pile in providing substantially the same lateral load-carrying capacity as a continuous larger diameter pile in frozen soil is that the point of maximum inflection along the length of the pile occurs on the pile approximately at the top surface of the permanently frozen region of the soil. That is, the stress distribution for a top laterally loaded pile is at a minimum at the point of loading and increases substantially uniformly along the length of the pile until it reaches the general area of the top surface of the permanently frozen region of the soil. Below the top surface of the permanently frozen region of the soil, the stress in the pile is reduced rapidly along the length of the pile until a point is reached along the length of the pile where little or zero stress is applied to the pile. Since the lowermost part of the pile provides little lateral load-carrying capacity, the total lateral load-carrying capacity of the pile can be increased merely by increasing the portion of the pile extending upwardly from within the permanently frozen region of the soil. While stepped pile and the advantages of stepped pile for use in permafrost are thus generally known, the maximum cost benefits have never been obtained.
SUMMARY OF THE INVENTION ~ ~ -It is an object of this invention to provide a large integral pile unit made of small, rigidly interconnected modular piles.
It is another object of this invention to provide a method of increasing the lateral load-carrying capacity of piles by integrally, rigidly interconnecting a plurality of small modular piles in a single hole into an integral unit.
It is still another object to increase the load-carrying capacity of piles in a less expensive manner than is presently employed.
Basically, these objects are obtained by a method of combining small piles and an apparatus which employs small, rigidly interconnected modular piles, preferably self-refrigerating or thermal piles, for use in a soil having a permenently frozen region. In the preferred embodiments, the rigid inter-connection is provided on the thermal pile with the same standard fins used in the thermal pile for increasing the heat dissipating capacity of the pile. The lateral load-carrying capacity of such an integral pile unit greatly exceeds ~ `
the sum of the lateral load-carrying capacities of each of the modular piles forming the unit. An advantage of such a pile unit is that small modular piles can be readily mass-produced, stored and shipped at substantially less cost than large piles. The small thermal piles are able to meet various government safety regulations for shipment of pressure vessels whereas a single large pile possibly could not. Furthermore, it is a much less expensive operation to form a large pile unit out of two or more small piles from a large inventory of small piles to meet the various load-carrying capacities necessary at different construction sites than to store an inventory of large piles of various sizes.
It is another object of this invention to provide an effective large-diameter but inexpensive stepped pile.
It is still another object of the invention to provide a pile unit formed from a plurality of modular piles, which pile unit also can be modified to form an inexpensive stepped pile unit.
It is still another object of this invention to provide a method of increasing the lateral load-carrying capacity of a single thermal pile or a multiple-pile, thermal pile unit in an inexpensive manner.
It is a principal object to provide a stepped pile unit for use in soil having a seasonally frozen region and a permanently frozen region, comprising at least one pile body having an upper end located in said seasonally frozen region and extending above the ground and a lower end extending into said permanently frozen region, elongated sleeve means encircling at least part of said upper end and extending downwardly along said lower end into said permanently frozen region, and means for structurally interconnecting the ;
sleeve means and pile body and spacing said sleeve means radially outwardly of said pile body to increase the effective diameter of the pile body down into the permanently frozen region.
Basically, these objects are obtained by providing a sleeve radially spaced from the pile body and encircling the pile body to a depth into the permanently frozen region below the point of maximum inflection of the pile. ~ -Fill material is then added around the pile within the hole and between the ~ -sleeve and the pile body. The soil within and around the sleeve in the perma-nently frozen region of the soil will rigidify to form an effective, largerdiameter~ -stepped upper end on the pile, with the fill in the seasonally frozen region also providing substantial lateral load-carrying capacity. If a plurality of modular piles are combined to form an integral pile unit, the sleeve will preferably encircle all of the piles in the unit in the hole, but less than all can be encircled, if desired. The use of a sleeve effectively increases the lateral load-carrying capacity of the pile and/or modular pile unit and also provides for a reduction in frost-jacking on the pile or pile unit. Fabrication of the sleeve can occur at the placement site, thus reducing shipping costs which would have been incurred if a stepped diameter pile had been employed.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic plan of a modular thermal pile unit embodying the principles of the invention;
Figure 2 is a fragmentary vertical section taken along the line 2-2 of Figure 1;
Figure 3 is a plan of a modular thermal pile unit employing a sleeve according to the principles of the invention;
Figure 4 is a side elevation of the thermal pile unit shown in Figure 3; and Figure 5 is a schematic diagram illustrating the stress in soil surrounding a pile, with Figure 5A illustrating a single pile having a sleeve according to the principles of the invention and Figure 5B illustrating a con-ventional thermal pile without the sleeve of this invention.
pETAlLED DESCRIPT!ON OF THE PREFERRED EMBODIMENTS
As best shown in Figures 1 and 2, a preferred modular thermal pile unit 10 includes a plurality of identical, individual thermal piles 12. Prefer-ably, each pile is generally of the type illustrated in United States Patent No. 3,217,791, although the principles of the invention are applicable also to other types of thermal piles and to conventional non-refrigerating-type piles.
The advantages of the invention, however, are best utilized on thermal piles which are provided with a plurality of standarized heat radiating fins 14. It is a unique feature of this invention, for example, that these fins can also be employed structurally to convert individual piles into a modular thermal pile unit 10.
The individual pile is essentially a pressure vessel having a valve 16 at its upper end for regulating the quantity of refrigerant in the pile.
The fins 14 are connected to the upper end of the pile, as by welding.
A load platform 18 is fixed to a collar or collars 19 that are preferably weldedto the upper ends of the fins. The collars can be welded in place after the piles are installed in the ground so that the plate 18 is horizontal and at the desired elevation. Alternatively, long collars can be welded to the fins during manufac-ture and then cut to desired lengths and the plate 18 added after the piles are i nsta 11 ed.
Adiacent overlapping standard fins 14a-14f are secured together, as by bolts, welding or rivets 20. Although three piles 12 have been shown forming the modular unit in Figure 1, it should be understood that two or numbers greater than three can be brought together into integral units in various configura-tions in a single hole to still obtain the benefits of the invention. Furthermore, the spacing between the piles can be increased to increase the lateral load-carrying capacity of the modular pile unit and the standardized fins still used for structural interconnection merely by reducing the amount of overlap between fins. The fins terminate general Iy above the ground level G, with the --piles extending down into the permafrost, as is well understood. As is readily apparent, the interconnection of the adjacent fins rigidly, structurally inter-connects the piles, forming an integral unit 10 which is capable of carrying lateral loads greatly exceeding the sum of the individual lateral load-carrying capacities of the individual piles. While the fins advantageously provide the means for interconnecting the piles, interconnecting structural members may be provided independent of or as a substitute for the fins. Furthermore, while longit~dir,al~fir~s~areiillustrated, horizontal fins may also advantageously be ~-employed, particularly in high wind velocity areas.
As best seen in Figures 3-5, the thermal pile unit 10 is shown with a unique sleeve 30 encircling the fins 14, being integrally secured thereto, andhaving a flange 30a which can extend inwardly or outwardly, as shown, or both.
While the sleeve is illustrated as encircling the terminal ends of the fins, it should be understood that the sleeve can be joined to the bottoms of the fins at a diameter inwardly from the terminal ends of the fins so as to reduce the diameter of the hole bored in the soil to accommodate the sleeve. AlternativelY, the sleeve can be slotted or the fins notched to allow placement of the sleeve inwardly of the perimeter of the fins. The size of the sleeve will be determined by the load-carrying capabilities or structural requirements desired and the , , ~ . . , ~ . , . :
.. . .
1045~37 characteristics of the soil in which the pile is to be used. In addition, although the sleeve is shown on a modular pile unit in Figures 3 and 4, it should be understood that it is equally suitable for use with a single pile 12, as shown in Figure 5A. Since the principles of operation and structure are essentially identical for a sleeved modular pile unit as for a sleeved single pile, for purposes of brevity a detailed drawing (other than Figure 5A) and description are not provided. Still further, although the sleeve is advantageously shown as connected to fins of a thermal pile, the sleeve may also be joined to the pile by struts or other braces rather than the fins, provided that this alterna-tive bracing allows the addition of fill between the pile and the sleeve.
As best shown in Figure 4, the sleeved pile unit also includes the platforms or plates 18 to carry the load L. If desired, radial, horizontal segments, rings or flexible blades 34 are added to the pile to increase its vertical load-carrying capacity, as described in more detail in United States Patents No. 3,706,204 and No. 3,797,257. The area between the piles of the pile unit 10 and between the individual piles 12 and the inside surface of the sleeve is filled with soil, gravel or any other suitable fill material normally used to fill the hole H in the soil. As is understood, the soil is of the type having a seasonally frozen region SF and a permanently frozen region PF, - 20 commoKl in permafrost or frozen soil areas in arctic regions. A generaly transi-tion area is defined by a line 40 which varies in depth, of course, according to the seasons of the year and environmental temperature above the ground, but for the purpose of this description, will be called the top of the permafrost region. Preferably, a layer of insulation 42 is laid on the ground level to reduce heating of the semi-frozen region during the warmer periods of the year. `
As is well understood, the individual sleeved pile or multiple-pile, sleeved pile unit will be assembled preferably at the job site where the hole H
has been prebored. The hole may have a larger diameter HL at the top which is of sufficient diameter to accommodate the sleeve 30; however, a uniform 30 diameter hole can be used. The pile unit will then be inserted into the hole and the fill added within and without the sleeve to integrally connect the fill with the permafrost soil. As is readily apparent, the solidification of the fill within the sleeve effectively makes a solid body between the pile and the sleeve, with the flange 30a providing a positive interlock into the frozen soil surrounding -6- :~
~
, ~ ' . . .
1~4~837 the sleeve. The effective diameter of the upper end of the pile is thus increased to that of the sleeve.
Figure 5 diagrammatically illustrates a comparison between an unstepped pile (Figure 5B) and a single stepped pile using the sleeve of this invention (Figure 5A), their approximate generalized stress diagrams both receiving the same lateral force applied at the arrow F. Curves are illustrated to represent an unstepped pile/frozen soil (USPF), an unstepped pile/unfrozen soil (USPUF), a stepped pile/frozen soil (SPF), and a stepped pile/unfrozen soil (SPUF). As is readily apparent, curve USPUF, for an unstepped pile/
unfrozen soil, starts at a minimum stress at the point of application of the force F and increases through about one-half the length of the pile, then decreases until it reaches a point near the bottom of the pile, again reaching zero stress.
A generalized curve USPF for the same unstepped pile in frozen soil shows a curve which also increases from zero at the point of the application of the force F, increasing to a maximum at the point of inflection 40 and then drastically falling off to zero shortly below the top surface of the permanently frozen region. Thus, the pile, in permanently frozen soil, carries very little lateral load in its lower length.
Curve SPUF shows the advantage gained by using a stepped pile in unfrozen soil. That is, the curve is shifted to the right or to the direction of increasing stress-carrying capacity in Figure 5. Like the curve USPUF, however, the stress distribution occurs along substantially the entire length of the pile, generally following curve USPUF at the lower end. Curve SPF
illustrates the increased lateral load-carrying capacity for the stepped pile in the frozen soil condition which allows for maximum lateral load-carrying capacity at a minimum increase in cost. For example, the larger diameter obtained from the sleeve 30 need not extend down below the line where zero stress distribution &gain occurs in ihe soil around the pile. Thus, it is readily apparent that by increasing the diameter of the pile down to and into the permanently frozen region, the total lateral load-carrying capacity of the pi l e is increased.
While the preferred embodiments of the invention have been illustrated and described, it should be understood that variations will be apparent to one skilled in the art without departing from the principles herein.
., . . . - : : . : . , . .: . . , :- : ~
1~45~337 Accordingly, the invention is not to be limited to the specific embodiments i I lustrated. ~ -~- .
, . . . . . .
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Field of the Invention This invention pertains to methods and apparatuses for increasing the vertical and, more importantly, the lateral load-carrying capacity of a pile or pile-like supports in soil having an upper, seasonally frozen region and a lower, permanently frozen region. The invention is especially useful with refrigerating-type thermal piles which have the capability of removing heat from the permanently frozen region of the soil to increase the load-carrying capacity of the surrounding soil.
DescriPtion of the Prior Art Thermal piles for use in increasing load-carrying capacity have been used heretofore. One such pile is described in my earlier United States patent, No. 3,217,791. The lowering of the temperature of the permanently frozen region of permafrost soil increases the vertical and lateral load-carrying capacity of the soil surrounding the pile.
The common technique for meeting the load-carrying capacity of the piles used in a large building is to increase the size or diameter of the piles at the numerous locations around the building. It is expensive to manufacture and transport large thermal piles due to their weight and size. It is also expensive due to the fact that a thermal pile unit is essentially a pressure vessel which must be manufactured according to strict specifications. Large pressure vessels are extremely expensive. The lateral load-carrying capacity of a large-diameter pile is frequently less than is required for a pile designed to have a certain vertical load-carrying capacity~ Consequently, large piles are either over-designed, with excess vertical load-carrying capacity, or cross-bracing between piles in holes spaced around the building is provided between adjacent piles to obtain the necessary lateral load-carrying capacity. Both solutions, however, are expensive.
Stepped piles, having larger diameters at their upper ends than at their lower ends, are known. A stepped pile is useful in permafrost having a lower, permanently frozen region since the larger stepped diameter can be terminated below the upper surface of the permanently frozen region and not extend the full length of the pile without substantially reducing the lateral load-carrying capacity of the pile. By stepping the pile, the remaining !ower ~,~ .
-1- ~F '' portion of the pile can be built of considerably less material, providing a sub-stantial cost savings. The reason for this characteristic of a stepped pile in providing substantially the same lateral load-carrying capacity as a continuous larger diameter pile in frozen soil is that the point of maximum inflection along the length of the pile occurs on the pile approximately at the top surface of the permanently frozen region of the soil. That is, the stress distribution for a top laterally loaded pile is at a minimum at the point of loading and increases substantially uniformly along the length of the pile until it reaches the general area of the top surface of the permanently frozen region of the soil. Below the top surface of the permanently frozen region of the soil, the stress in the pile is reduced rapidly along the length of the pile until a point is reached along the length of the pile where little or zero stress is applied to the pile. Since the lowermost part of the pile provides little lateral load-carrying capacity, the total lateral load-carrying capacity of the pile can be increased merely by increasing the portion of the pile extending upwardly from within the permanently frozen region of the soil. While stepped pile and the advantages of stepped pile for use in permafrost are thus generally known, the maximum cost benefits have never been obtained.
SUMMARY OF THE INVENTION ~ ~ -It is an object of this invention to provide a large integral pile unit made of small, rigidly interconnected modular piles.
It is another object of this invention to provide a method of increasing the lateral load-carrying capacity of piles by integrally, rigidly interconnecting a plurality of small modular piles in a single hole into an integral unit.
It is still another object to increase the load-carrying capacity of piles in a less expensive manner than is presently employed.
Basically, these objects are obtained by a method of combining small piles and an apparatus which employs small, rigidly interconnected modular piles, preferably self-refrigerating or thermal piles, for use in a soil having a permenently frozen region. In the preferred embodiments, the rigid inter-connection is provided on the thermal pile with the same standard fins used in the thermal pile for increasing the heat dissipating capacity of the pile. The lateral load-carrying capacity of such an integral pile unit greatly exceeds ~ `
the sum of the lateral load-carrying capacities of each of the modular piles forming the unit. An advantage of such a pile unit is that small modular piles can be readily mass-produced, stored and shipped at substantially less cost than large piles. The small thermal piles are able to meet various government safety regulations for shipment of pressure vessels whereas a single large pile possibly could not. Furthermore, it is a much less expensive operation to form a large pile unit out of two or more small piles from a large inventory of small piles to meet the various load-carrying capacities necessary at different construction sites than to store an inventory of large piles of various sizes.
It is another object of this invention to provide an effective large-diameter but inexpensive stepped pile.
It is still another object of the invention to provide a pile unit formed from a plurality of modular piles, which pile unit also can be modified to form an inexpensive stepped pile unit.
It is still another object of this invention to provide a method of increasing the lateral load-carrying capacity of a single thermal pile or a multiple-pile, thermal pile unit in an inexpensive manner.
It is a principal object to provide a stepped pile unit for use in soil having a seasonally frozen region and a permanently frozen region, comprising at least one pile body having an upper end located in said seasonally frozen region and extending above the ground and a lower end extending into said permanently frozen region, elongated sleeve means encircling at least part of said upper end and extending downwardly along said lower end into said permanently frozen region, and means for structurally interconnecting the ;
sleeve means and pile body and spacing said sleeve means radially outwardly of said pile body to increase the effective diameter of the pile body down into the permanently frozen region.
Basically, these objects are obtained by providing a sleeve radially spaced from the pile body and encircling the pile body to a depth into the permanently frozen region below the point of maximum inflection of the pile. ~ -Fill material is then added around the pile within the hole and between the ~ -sleeve and the pile body. The soil within and around the sleeve in the perma-nently frozen region of the soil will rigidify to form an effective, largerdiameter~ -stepped upper end on the pile, with the fill in the seasonally frozen region also providing substantial lateral load-carrying capacity. If a plurality of modular piles are combined to form an integral pile unit, the sleeve will preferably encircle all of the piles in the unit in the hole, but less than all can be encircled, if desired. The use of a sleeve effectively increases the lateral load-carrying capacity of the pile and/or modular pile unit and also provides for a reduction in frost-jacking on the pile or pile unit. Fabrication of the sleeve can occur at the placement site, thus reducing shipping costs which would have been incurred if a stepped diameter pile had been employed.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic plan of a modular thermal pile unit embodying the principles of the invention;
Figure 2 is a fragmentary vertical section taken along the line 2-2 of Figure 1;
Figure 3 is a plan of a modular thermal pile unit employing a sleeve according to the principles of the invention;
Figure 4 is a side elevation of the thermal pile unit shown in Figure 3; and Figure 5 is a schematic diagram illustrating the stress in soil surrounding a pile, with Figure 5A illustrating a single pile having a sleeve according to the principles of the invention and Figure 5B illustrating a con-ventional thermal pile without the sleeve of this invention.
pETAlLED DESCRIPT!ON OF THE PREFERRED EMBODIMENTS
As best shown in Figures 1 and 2, a preferred modular thermal pile unit 10 includes a plurality of identical, individual thermal piles 12. Prefer-ably, each pile is generally of the type illustrated in United States Patent No. 3,217,791, although the principles of the invention are applicable also to other types of thermal piles and to conventional non-refrigerating-type piles.
The advantages of the invention, however, are best utilized on thermal piles which are provided with a plurality of standarized heat radiating fins 14. It is a unique feature of this invention, for example, that these fins can also be employed structurally to convert individual piles into a modular thermal pile unit 10.
The individual pile is essentially a pressure vessel having a valve 16 at its upper end for regulating the quantity of refrigerant in the pile.
The fins 14 are connected to the upper end of the pile, as by welding.
A load platform 18 is fixed to a collar or collars 19 that are preferably weldedto the upper ends of the fins. The collars can be welded in place after the piles are installed in the ground so that the plate 18 is horizontal and at the desired elevation. Alternatively, long collars can be welded to the fins during manufac-ture and then cut to desired lengths and the plate 18 added after the piles are i nsta 11 ed.
Adiacent overlapping standard fins 14a-14f are secured together, as by bolts, welding or rivets 20. Although three piles 12 have been shown forming the modular unit in Figure 1, it should be understood that two or numbers greater than three can be brought together into integral units in various configura-tions in a single hole to still obtain the benefits of the invention. Furthermore, the spacing between the piles can be increased to increase the lateral load-carrying capacity of the modular pile unit and the standardized fins still used for structural interconnection merely by reducing the amount of overlap between fins. The fins terminate general Iy above the ground level G, with the --piles extending down into the permafrost, as is well understood. As is readily apparent, the interconnection of the adjacent fins rigidly, structurally inter-connects the piles, forming an integral unit 10 which is capable of carrying lateral loads greatly exceeding the sum of the individual lateral load-carrying capacities of the individual piles. While the fins advantageously provide the means for interconnecting the piles, interconnecting structural members may be provided independent of or as a substitute for the fins. Furthermore, while longit~dir,al~fir~s~areiillustrated, horizontal fins may also advantageously be ~-employed, particularly in high wind velocity areas.
As best seen in Figures 3-5, the thermal pile unit 10 is shown with a unique sleeve 30 encircling the fins 14, being integrally secured thereto, andhaving a flange 30a which can extend inwardly or outwardly, as shown, or both.
While the sleeve is illustrated as encircling the terminal ends of the fins, it should be understood that the sleeve can be joined to the bottoms of the fins at a diameter inwardly from the terminal ends of the fins so as to reduce the diameter of the hole bored in the soil to accommodate the sleeve. AlternativelY, the sleeve can be slotted or the fins notched to allow placement of the sleeve inwardly of the perimeter of the fins. The size of the sleeve will be determined by the load-carrying capabilities or structural requirements desired and the , , ~ . . , ~ . , . :
.. . .
1045~37 characteristics of the soil in which the pile is to be used. In addition, although the sleeve is shown on a modular pile unit in Figures 3 and 4, it should be understood that it is equally suitable for use with a single pile 12, as shown in Figure 5A. Since the principles of operation and structure are essentially identical for a sleeved modular pile unit as for a sleeved single pile, for purposes of brevity a detailed drawing (other than Figure 5A) and description are not provided. Still further, although the sleeve is advantageously shown as connected to fins of a thermal pile, the sleeve may also be joined to the pile by struts or other braces rather than the fins, provided that this alterna-tive bracing allows the addition of fill between the pile and the sleeve.
As best shown in Figure 4, the sleeved pile unit also includes the platforms or plates 18 to carry the load L. If desired, radial, horizontal segments, rings or flexible blades 34 are added to the pile to increase its vertical load-carrying capacity, as described in more detail in United States Patents No. 3,706,204 and No. 3,797,257. The area between the piles of the pile unit 10 and between the individual piles 12 and the inside surface of the sleeve is filled with soil, gravel or any other suitable fill material normally used to fill the hole H in the soil. As is understood, the soil is of the type having a seasonally frozen region SF and a permanently frozen region PF, - 20 commoKl in permafrost or frozen soil areas in arctic regions. A generaly transi-tion area is defined by a line 40 which varies in depth, of course, according to the seasons of the year and environmental temperature above the ground, but for the purpose of this description, will be called the top of the permafrost region. Preferably, a layer of insulation 42 is laid on the ground level to reduce heating of the semi-frozen region during the warmer periods of the year. `
As is well understood, the individual sleeved pile or multiple-pile, sleeved pile unit will be assembled preferably at the job site where the hole H
has been prebored. The hole may have a larger diameter HL at the top which is of sufficient diameter to accommodate the sleeve 30; however, a uniform 30 diameter hole can be used. The pile unit will then be inserted into the hole and the fill added within and without the sleeve to integrally connect the fill with the permafrost soil. As is readily apparent, the solidification of the fill within the sleeve effectively makes a solid body between the pile and the sleeve, with the flange 30a providing a positive interlock into the frozen soil surrounding -6- :~
~
, ~ ' . . .
1~4~837 the sleeve. The effective diameter of the upper end of the pile is thus increased to that of the sleeve.
Figure 5 diagrammatically illustrates a comparison between an unstepped pile (Figure 5B) and a single stepped pile using the sleeve of this invention (Figure 5A), their approximate generalized stress diagrams both receiving the same lateral force applied at the arrow F. Curves are illustrated to represent an unstepped pile/frozen soil (USPF), an unstepped pile/unfrozen soil (USPUF), a stepped pile/frozen soil (SPF), and a stepped pile/unfrozen soil (SPUF). As is readily apparent, curve USPUF, for an unstepped pile/
unfrozen soil, starts at a minimum stress at the point of application of the force F and increases through about one-half the length of the pile, then decreases until it reaches a point near the bottom of the pile, again reaching zero stress.
A generalized curve USPF for the same unstepped pile in frozen soil shows a curve which also increases from zero at the point of the application of the force F, increasing to a maximum at the point of inflection 40 and then drastically falling off to zero shortly below the top surface of the permanently frozen region. Thus, the pile, in permanently frozen soil, carries very little lateral load in its lower length.
Curve SPUF shows the advantage gained by using a stepped pile in unfrozen soil. That is, the curve is shifted to the right or to the direction of increasing stress-carrying capacity in Figure 5. Like the curve USPUF, however, the stress distribution occurs along substantially the entire length of the pile, generally following curve USPUF at the lower end. Curve SPF
illustrates the increased lateral load-carrying capacity for the stepped pile in the frozen soil condition which allows for maximum lateral load-carrying capacity at a minimum increase in cost. For example, the larger diameter obtained from the sleeve 30 need not extend down below the line where zero stress distribution &gain occurs in ihe soil around the pile. Thus, it is readily apparent that by increasing the diameter of the pile down to and into the permanently frozen region, the total lateral load-carrying capacity of the pi l e is increased.
While the preferred embodiments of the invention have been illustrated and described, it should be understood that variations will be apparent to one skilled in the art without departing from the principles herein.
., . . . - : : . : . , . .: . . , :- : ~
1~45~337 Accordingly, the invention is not to be limited to the specific embodiments i I lustrated. ~ -~- .
, . . . . . .
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Claims (9)
1. A stepped pile unit for use in soil having a seasonally frozen region and a permanently frozen region, comprising at least one pile body having an upper end located in said seasonally frozen region and extending above the ground and a lower end extending into said permanently frozen region, elongated sleeve means encircling at least part of said upper end and extending downwardly along said lower end into said permanently frozen region, and means for structurally interconnecting the sleeve means and pile body for spacing said sleeve means radially outwardly of said pile body to increase the effective diameter of the pile body down into the permanently frozen region.
2. The stepped pile unit of claim 1, said upper end of said pile body having a plurality of radially extending, circumferentially spaced fins protruding outwardly above ground, said means for spacing said sleeve radially outwardly including a portion of said fins.
3. The stepped pile unit of claim 1, including a plurality of addi-tional identical pile bodies and means rigidly interconnecting said pile bodies in symmetrical spaced array, said sleeve spaced from, interconnected to and encircling all of said interconnected pile bodies.
4. The stepped pile unit of claim 3, each pile body having a plurality of radially extending fins circumferentially spaced around its upper end, said means for rigidly interconnecting said pile bodies including a portion of said fins.
5. The stepped pile unit of claim 1, said sleeve having a lower end provided with a radially extending flange.
6. A method of increasing the lateral load-carrying capacity of an elongated pile in a soil having a seasonally frozen upper region and a permanently frozen lower region, comprising:
forming a hole with at least an upper end of a diameter substan-tially larger than the pile diameter in the soil through the seasonally frozen region and into the permanently frozen region, adding an elongated sleeve around only an upper end of the pile and spaced therefrom, rigidly interconnecting the pile and sleeve, lowering the pile and sleeve into the hole until the lower end of the sleeve extends into the permanently frozen region, and filling the hole around the pile and sleeve and between the pile and sleeve to form a fill layer trapped between the sleeve and the pile to effectively radially extend the diameter of the pile to the diameter of the sleeve to a line below the upper surface of the permanently frozen region.
forming a hole with at least an upper end of a diameter substan-tially larger than the pile diameter in the soil through the seasonally frozen region and into the permanently frozen region, adding an elongated sleeve around only an upper end of the pile and spaced therefrom, rigidly interconnecting the pile and sleeve, lowering the pile and sleeve into the hole until the lower end of the sleeve extends into the permanently frozen region, and filling the hole around the pile and sleeve and between the pile and sleeve to form a fill layer trapped between the sleeve and the pile to effectively radially extend the diameter of the pile to the diameter of the sleeve to a line below the upper surface of the permanently frozen region.
7. The method of claim 6, including the step of cooling the soil around the lower end of the pile to reduce the temperature of the permanently frozen region.
8. The method of claim 6, including structurally, rigidly inter-connecting a plurality of piles to form an integral pile unit, providing said elongated sleeve around said pile unit, rigidly interconnecting said sleeve to said pile unit, forming at least the upper end of the hole to a diameter greater than the diameter of said pile unit plurality of piles, lowering the pile unit into the hole with the sleeve terminating within the permanently frozen region, and filling the hole around and between said piles of said pile unit and between said sleeve and said pile unit to increase the effective diameter of said pile unit.
9. The method of claim 8, including the step of cooling the lower end of the pile unit to lower the temperature of the permanently frozen region and rigidify the trapped fill.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/587,917 US4067198A (en) | 1975-06-18 | 1975-06-18 | Method and structural support for increasing load carrying capacity in permafrost |
| CA251,034A CA1034777A (en) | 1975-06-18 | 1976-04-26 | Method and structural support for increasing load-carrying capacity in permafrost |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1045837A true CA1045837A (en) | 1979-01-09 |
Family
ID=25668278
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA300,620A Expired CA1045837A (en) | 1975-06-18 | 1978-04-06 | Method and structural support for increasing load-carrying capacity in permafrost |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1045837A (en) |
-
1978
- 1978-04-06 CA CA300,620A patent/CA1045837A/en not_active Expired
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