Device and Method for Improved Pile Casting
This invention deals with a device and a method for an improved concrete pile casting in swelling soils by substantially lowering or eliminating heave forces created in active soils from affecting said piles by surrounding selectable parts of the pile by an easily deformable material for lowering the horizontal and the vertical soil movement effect, and by providing a low friction surface for further lowering vertical forces effect. This inventive device and method further facilitates subsequent operations by permitting an easy and seamless casting of columns and by ensuring a clean and smooth pile surface for a better adhesion of new concrete to an old one, as well as preventing cement dough seepage to surrounding soil and concrete segregation.
This invention deals with a device for the neutralization, i.d. the lowering or the elimination, of heave forces acting on piles sunk in certain types of expansive soils and for the improvement of the properties of cast in situ piles.
BACKGROUND OF THE INVENTIONCertain types of soils, such as clay and marl, swell when absorbing water and shrink when this water is exuded. Water is usually absorbed by soils during the rainy season and exuded by evaporation and the like during the dry season. The shrinkage leads to cracks which can be several meters deep and ten centimeters wide, depending on many factors. The soil depth in which this phenomenon occurs is called the active depth hereinbelow, and may not be uniform. In a rainy season following a dry one, water tends to flow into the cracks and leads to soil swelling, which also closes the cracks, and in the following dry season the soil shrinks to create cracks. Thus an annual soil shrinkage-swelling cycle occurs. Also, water from other sources, such as water used during construction or for irrigation could flow into soil cracks during a dry season and cause soil swelling. Both the soil shrinkage and the soil swelling lead to soil movements. These movements cause substantial pressures, stresses and forces, called heave pressures, which may reach, according to various sources, 20 to 80 tonnes/m**2. The heave forces tend to decrease with depth, the soil depth in which the forces and movements exist, or are still significant is called active soil depth. As the soil movement is three dimensional, so are the heave forces, which have both horizontal and vertical components. A conventional designation of the vertically pointing heave forces is positive, if pointing upward. Vertically forces pointing downward are commonly designated negative skin friction, and are caused by fill settlement. The heave forces act on piles and the like built in active soils, and the pressures, summed over the pile circumference, are known to cause severe structural damage. The term “pile” as used hereinbelow refers mainly to founding piles and to other piles in contact with soil along at least part of their lengths and circumferences, such as retaining walls piles. The vertical heave forces act on underground structural elements such as piles and the like either by creating friction forces, which are upward or downward pointing, or by applying pressure on non vertical, horizontal or inclined, surfaces of these elements. The vertical heave forces exceed the design load acting on the pile by low-rise buildings and may exceed the load acting on the pile, in higher/heavier buildings, especially during mid-construction, when the design load is not yet applied. Desiccation of the soil in the active depth causes pile settlement. This heave or settlement may be differential among piles, thus leading to cracks in the supported structure. The horizontal forces may bend, shear and tilt the piles, cracking them and any supported structures. Either way, damage to the piles and to the supported structures often ensues. The advantage of neutralizing the heave forces is, therefore, obvious. It should be pointed out that the seasonal soil moisture contents variation tends to be lower for the soil underneath a structure, which is not exposed to weather conditions and relatively protected temperature changes, and higher for an exposed soil which is affected by the weather conditions. Thus, piles may be subjected to circumferentially varying pressures.
Another soil phenomenon handled by this inventive device and method is the collapse of the walls of boreholes bored in certain types of soils, such as sand and fill, into the borehole before or during the casting of the pile. The soil layer in which this collapse may occur, such as sand and fill, may be called unstable or active layer, and its depth is called the active depth. Such collapse fills parts of the borehole with soil and may cause pile shortening, partial concrete filling along some pile sections or even concrete discontinuity with negative structural consequences.
Still another problem caused by the collapse of soil around the bore head is that a roughly inverted conical depression is formed in the collapsed soil region at the upper part of the soil around the bore mouth, and, when filled by concrete, forms a mushroom shaped pile. This effect is particularly harmful in swelling soils. Heave forces acting on such mushroom, in addition to their effects elsewhere, may raise the pile, cause tension forces, crack it and the supported structure and lead to other problems.
Yet another problem is the seepage of concrete dough into porous soil such as fill, in contact with the concrete. This seepage weakens the concrete. The seepage and the segregation are further aggravated by compacting the concrete, a process often required.
Six problems addressed and solved or alleviated by this invention are listed below:
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- 1. The creation of vertical and horizontal heave forces on founding piles.
- 2. The creation of negative skin friction or heave forces on founding piles.
- 3. The collapse of soil such as fill soil at the upper part of a borehole and the created mushroom like depression, and the forces created by the settling of the soil.
- 4. The creation of heave forces acting on partly or fully embedded piles of retaining walls, such as basement walls, the cleaning of the piles prior to the application of anti moisture materials and the sealing of the gaps between the piles.
- 5. The problem of the seam between the top part of a pile and an aboveground column extending away from it.
- 6. The seepage of cement dough into a porous soil such as fill soil and the resulted weakening of the concrete, or segregation. This problem is aggravated when the top part of the concrete is compacted.
No device or method for economically fully solving the abovementioned problems have been developed so far, although partial attempt is shown in GB Patent 2283266 to Sloma.
One conventional way of attempting to overcome the abovementioned problems is by extending the piles to substantially greater depths than the ones required in the absence of heave forces. Such extension is always expensive and often impractical, as bedrock or water table may be encountered. Of course, this conventional way does not eliminate the heave forces reaching the pile and leading to tension stresses. These stresses might lead to pile cracking or failure and require added reinforcement. This inventive device eliminates, or greatly reduces, the need for such pile extension. Another conventional way used is the building of a so called membrane around the structure, the membrane being several meters wide and made of impermeable materials such as concrete or asphalt, to prevent or to lower the moisture fluctuations near the piles. This conventional solution, as the previous one, is expensive and often impractical.
The manner in which this inventive device solves the abovementioned problems is shown below in this document.
SUMMARY OF THIS INVENTIONThree concentric sleeves of the same length are the essential elements of this invention:
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- An inner sleeve which serves as a mold for the upper part of a pile, and is preferably fairly rigid and water impermeable, encompassed by:
- A filling sleeve, made of a thick, highly deformable, low modulus material, encompassed by:
- An outer sleeve, made of a thin sheet having low friction coefficient between it and might be formed of two layers,
The inner sleeve also supports its weight and that of the other two sleeves. The filling sleeve is intended to be deformed by the horizontal and the vertical forces created by the soil movements, therefore passing only a small part of the potential soil forces to the pile. The low friction between the outer sleeve and the encompassed sleeve, passes only a small part of the vertical forces created by the soil movements to the filling sleeve and to the pile.
The sleeve dimensions and materials are to be selected according to the particular conditions of each project.
The manner in which this inventive device neutralizes the heave forces that affect piles and the like, is elaborated in the following explanation of
Therefore, this embodiment 21 of the inventive design incorporates five elements: an inner sleeve 22, an outer sleeve 23, a filling sleeve 24, at least one spacer 26, and sealing rings 25. Top and bottom sealing rings 25 may be used for fastening one or two extremities of 23 to the respective extremity or extremities of 24 and 22. In this inventive design, elements 22, 23, 24 are required and elements 25, 26 are optional. Membrane 28 may be added to lower moisture fluctuations around pile 29.
It should be understood that the term cylinder and terms derived therefrom also refer to a sheet bent along approximately to circular arc of any angle, but typically between somewhat below 180 degrees and somewhat above 360 degrees, or a tubular shell extending from 360 degrees and below.
Sleeve 22 may be made of a flexible sheet bent to a cylindrical arcuate shape, its flexibility pushing sleeves 23, 24 against borehole 230, the arc formed by 22, 23, 24 may be 360 degrees or somewhat above it, as shown in this embodiment, to form at least part of this inventive device, or it may be any other angle, such as somewhat less than 180 degrees, as shown by in
Sleeve 21 may also be made by encompassing tube or pipe forming 22 by tube or pipe forming 24 and encompassing 24 by a sleeve or sheet 23, or by any desired combination of bent sheets and tubes.
Sleeve 21, or any number of its constitutive parts such as 22, 23, 24, 25, 26, may be held in place before the 11ing of the concrete by any means such as by tying it to 27 at a desirable place, securing it to 29 or by other means known in the trade.
Means other than 26 for separating 22 and 27 could be used, and membrane 28 may not be necessary or practical in many circumstances.
The designation of the elements in the subsequent Figs. that are similar to 22, 23, 24, 25, 26 in
It is known that fill soil such as 211 in
The inventive device shown and claimed in this document may be made of any materials suitable for its conditions of use, such as the particular environmental conditions and the applied forces. For example, while plastic materials may often be used for the parts illustrated in the embodiments of this document, other materials such as cardboard, wood, steel which may be painted or galvanized, and many others, may also be used, the materials listed in this paragraph being strictly exemplary and presented as non limiting list only, are not an exhaustive list and do not limit the scope of this invention. The dimensions shown in this document are also exemplary and non limiting only, different dimensions and materials may be used if deemed desirable or necessary. Sleeves 22,23,24 may be made by cutting and bending sheets of the respective materials in situ, by cutting tubes, or any or all of them may be prepared elsewhere, and brought to the construction site ready for assembly.
Also, while a single unit of this inventive device is shown in the accompanying figures, a number of inventive devices, preferably mounted one on top of each other, may be used for a single pile without limiting the scope of this invention. Furthermore, this inventive device may be used only for the underground parts of a pile while a different device or method may be used for any aboveground parts of a pile, which are not subject to moisture induced and other soil effects.
It is to be understood that there is not a clear and constant separation level, such as 218 in
It is also to be understood that the borehole diameter may be increased in parts such as the borehole section that receives this inventive device, so that the pile diameter is constant, although in the embodiments shown in this document the borehole diameter is constant and the pile diameter is reduced by twice the sleeves 22, 23, 24 thicknesses where encompassing the sleeve.
Therefore, this embodiment 31 of the inventive design incorporates six elements: an inner ring 32, an outer sleeve 33, a filling sleeve 34, at least one spacer 36, sealing rings 35. In this inventive design, elements 32, 33, 34 are required and elements 35, 36 are optional. Membrane 38 may be added to lower moisture fluctuations.
Means other than 36 for separating 32 and 37 could be used, and membrane 38 may not be necessary or practical in many circumstances.
Therefore, this embodiment 41 of the inventive design incorporates five elements: an inner ring 42, an outer sleeve 43, a filling sleeve 44, at least one spacer 46, sealing rings 45. In this inventive design, elements 42, 43, 44 are required and elements 45, 46 are optional. Membrane 48 may be added.
Means other than 46 for separating 42 and 47 could be used, and membrane 48 may not be necessary or practical in many circumstances.
A number of boreholes 930 for piles 99 are bored in soil 921 which may be fill, active or both, and reinforcement cages 97 are inserted therein. A relatively rigid inner sleeve 92, filling sleeve 94, preferably made of deformable, low modulus material, and a relatively rigid outer sleeve 93 are inserted into each borehole 930, grooves are cut through said sleeves and inserts 920, preferably in contact with cages 97 are inserted into grooves 922. Spacers 920 are made or rubber or other suitable material to be easily removable, as elaborated hereinbelow. One side of each one of grooves 922 is positioned to define the contact area of support wall 923, to be cast later, with soil 921, said defining sides of said grooves being preferably coplanar. Additional spacers, not shown, separating 92 from 97, may be added. Concrete 916 is cast in boreholes 930 to form piles 99. Soil 921 is then dug out in the support wall side of piles 99, the left side in this exemplary figure, and the portions of 92, 93, 94 in that support wall side as well as 920 are removed, exposing clean pile surfaces and grooves 922 in piles 99. Concrete 911 to form wall 923 is then cast. There is no need to clean the exposed parts of piles 99, and grooves 922 insure a good contact between wall 923 and piles 99. Furthermore, much better water sealing properties are obtained by the penetration of the concrete of 911 into grooves 922 of piles 99.
Therefore, this embodiment 111 of the inventive design incorporates five elements: an inner sleeve 112, an outer sleeve 113, a filling sleeve 114, spacers 116, and sealing rings 115. In this inventive design, elements 112, 113, 114 are required and elements 115, 116 are optional. Membrane 118 may be added to lower moisture fluctuations.
Means other than 36 for separating 32 and 37 could be used, and membrane 118 may not be necessary or practical in many circumstances.
It will be appreciated by persons skilled in the art, that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention is defined by the appended claims and includes both combinations and sub-combinations of the various features described hereinabove as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description.
Claims
1. A device for in-situ casting of at least partly underground concrete pile within a borehole having a mouth, said borehole having a reinforcing cage at least partially disposed therein, said device comprising:
- A cylindrical inner sleeve mountable within said borehole for casting said pile, said inner sleeve having a length, an upper extremity and a lower extremity, and dimensioned to at least partially surround said reinforcement cage;
- A filling sleeve having an upper extremity and a lower extremity and having substantially the same length as the length of said inner sleeve, said filling sleeve dimensioned to circumferentially encompass said inner sleeve, said filling sleeve being substantially deformable and made of material having a low elastic modulus;
- An outer sleeve having an upper extremity and a lower extremity and having substantially the same length as said inner and filling sleeves, said outer sleeve dimensioned to circumferentially encompass said filling sleeve, said outer sleeve and said filling sleeve having a low coefficient of friction therebetween,
- Wherein said lower extremities of said inner, filling, and outer sleeves are substantially coplanar when deployed within said borehole for affecting said casting.
2. A device according to claim 1 further comprising a sealing ring, said sealing ring dimensioned to be coupled at least to an extremity of said filling sleeve and to a matching extremity of said outer sleeve.
3. A device according to claim 1 further comprising a spacer for spacing apart said inner sleeve and said cage.
4. A device according to claim 1 wherein said outer sleeve comprises at least two essentially congruent layers.
5. A device according to claim 1 wherein any of said sleeves comprises a bent sheet.
6. A device according to claim 1 wherein at least one of said inner sleeve and filling sleeve is expandable for securing said outer sleeve to said borehole wall.
7. A device according to claim 1 wherein any of said sleeves comprises a tube.
8. A device according to claim 1 wherein any of said sleeves comprises of polymeric material.
9. A device according to claim 1 wherein said inner sleeve comprises of cardboard.
10. A device according to claim 1 wherein said inner sleeve comprises of metal.
11. A method for in situ casting of at least partly underground concrete pile within a borehole, said borehole having a reinforcing cage therein and having a mouth, said method comprising any sequence of the steps of: wherein each sleeve having a top extremity and a bottom extremity, and wherein said top extremities are coplanar and said bottom extremities are coplanar, wherein said outer sleeve encompasses said filling sleeve, said filling sleeve encompasses said inner sleeve, and only said bottom extremities are below said mouth, said outer sleeve having a low friction coefficient at the interface between itself and its encompassed sleeve.
- inserting a cylindrical inner sleeve mountable within said borehole for casting said pile, said sleeve having a length, said sleeve surrounding at least a part of said cage;
- inserting a filling sleeve having substantially the same said length, said filling sleeve made of substantially low elastic modulus and substantially deformable material
- inserting an outer sleeve having substantially the same said length,
12. A method according to claim 11 further comprising the step of attaching a sealing ring extending between an extremity of said filling sleeve and said outer sleeve.
13. A method according to claim 11 further comprising the step of inserting a spacer, said spacer being inserted between said inner sleeve and said cage for spacing apart said inner sleeve from said cage.
14. A method according to claim 11 wherein said outer sleeve comprises at least two substantially congruent layers.
15. A method according to claim 11 wherein any of said sleeves is formed of a bent sheet.
16. A method according to claim 11 further comprising the step of elastically bending at least one of said inner sleeve and said filling sleeve to expand and secure said outer sleeve to said borehole wall.
17. A method according to claim 11 wherein any of said sleeves is formed of a tube.
18. A method according to claim 11 wherein any of said sleeves comprises polymeric material.
19. A method according to claim 11 wherein said inner sleeve is formed of cardboard.
20. A method according to claim 11 wherein said inner sleeve is formed of metal.
Type: Application
Filed: Jun 24, 2007
Publication Date: Nov 12, 2009
Inventor: Basem Hazzan (Akko)
Application Number: 12/305,488
International Classification: E02D 5/00 (20060101); E02D 5/58 (20060101);