Abstract:
A poured concrete slab foundation which has a first component comprising a poured concrete slab on soil, having at least one interior grade beam, grade beams about the periphery of said poured concrete slab, and an array of openings along and adjacent to each said interior grade beam; a second component comprising an array of driven piles in the soil below said interior and periphery grade beams; and a third component comprising poured concrete closures in said openings, which is made by preparing a poured concrete slab on soil, having at least one interior grade beam, grade beams about the periphery of said poured concrete slab, and an array of openings along and adjacent to each said interior grade beam; driving an array of pilings in the soil below said interior grade beams adjacent to the openings and the periphery grade beams and pouring concrete closures in said openings.

Description:
[0001]     This application claims the benefit of provisional application 60/678,059 filed May 5, 2005. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates to building foundations. More specifically, it relates to a method for building a poured concrete foundation which more effectively isolates the foundation from the ground heave of the soil on which it is built.  
         [0004]     2. Related Art  
         [0005]     Many types of structures, such as residential homes, commercial buildings and industrial equipment, are erected on foundations or slabs made of concrete poured on top of soil. These foundations are typically concrete slabs and may include a concrete footing that is wider and deeper than the foundation to spread the load of the foundation and carried structure. Ultimately the structural integrity and the level of the foundation and the carried structure are dependent on the stability of the underlying soil. Extreme cyclic weather changes greatly increase the chance for foundation failure. This failure can be in the form of settlement or heave. High clay content soils are of particular concern. The changes in the supporting soil often result in damage to the structural integrity of the foundation and the carried structure and/or producing a non-level foundation. This phenomenon occurs because prior to placing the foundation on the ground, the moisture beneath it is relatively constant. Placing a foundation on the soil changes that footprint and distorts the equilibrium of the moisture underneath the foundation. Left uncorrected, the settling of the soil and lack of stability of the foundation may result in loss of part or all of the value of the foundation and carried structure. Due to the frequency of damage to foundations from soil settlement many foundation repair systems have been installed in an attempt to stabilize the foundation and to correct positioning of the foundation.  
         [0006]     There are several methods used in repairing foundations, some more effective than others. One of the most effective and widely used methods includes the use of one or more piles or piers submerged into the soil beneath the foundation to form one or more supports.  
         [0007]     In such a procedure, there are several ways to construct and position a pile. Regardless of the manner in which a pile is constructed, however, most are made primarily of concrete and/or steel and have an overall cylindrical shape with a length varying according to the soil type and weight of the structure.  
         [0008]     Repairs to “multiple owned” common slab units are almost impossible to coordinate. Getting each individual unit to agree to spend the money, accept the fact that it has a problem and settle on one single contractor is a difficult task. Having a warranted slab takes the risk out of being at the mercy of each neighbor in order to repair your home and protect your investment.  
         [0009]     Most existing home warranties do not correct foundation movement unless the home is considered unsafe or uninhabitable. Current methods of underpinning new homes to date have been very limited and the type of pier typically used in new construction is the same pier (poured in-place bell bottom piers) that has become somewhat obsolete in some parts of the U.S. to the foundation repair industry.  
         [0010]     The problems of foundation movement are not restricted to older homes. Many foundation repairs are made to “new” homes, i.e., homes less than 10 years old and as new as only 1-3 years old.  
         [0011]     Now the method of repair uses precast concrete pile segments comprising vertically stacked, precast concrete segments. These segments are pressed or driven vertically into the soil one at a time until an adequate load carrying capacity is obtained by frictional resistance. This system came into favor because it required low clearance under the structure being leveled and did not require a predrilled hole with concurrent hauling of removed dirt and pouring of cement.  
         [0012]     Although settlement may be a problem at times, it would appear that in expansive soils, the major cause of foundation damage to new homes is the result of soil heaving or swelling. The solution to preventing foundation damage is to keep the foundation off the moving soil, which is of course not literally possible, thus the next best solution is to have as little of the foundation as possible in contact with the soil. This technique is used in a modified concrete slab foundation, whereby the beams are poured on poured in-place bell bottom piers and “crates” are positioned between the soil and the major portion of the concrete foundation between the beams. The crates are corrugated cardboard boxes, which provide adequate support for the concrete during the pour, but crumple when the soil heaves, thereby preventing the soil from contact with the major portion of the foundation, while the beams are isolated from the heaving soil by the piers. This is a very expensive foundation and even with these precautions there may be foundation issues during construction as a result of the failure of the poured piers.  
         [0013]     It is an advantage of the present foundation system that all foundations can be manufactured with the advantages of the isolation of the major portion of the foundations from the soil without the drawbacks of the poured piers and at substantially lower cost. A particular advantage of the present foundation system is that the sought after isolation of the foundation from the soil will become a closer reality than now achieved by prior construction systems.  
         [0014]     That which distinguishes the present invention from the prior art is the novel means of combining new construction and repair technologies to come the closest yet to isolating poured concrete slab foundations from the soil and the resultant instabilities. The method of this invention is designed to help reduce the cost of remedial foundation leveling. This invention will reduce the cost of building foundations on expansive soils. Many new homes (less than  5  years old) are experiencing unacceptable foundation movement. Most of this movement is in the form of upward vertical movement. Vast amounts of money are spent to design and install a concrete slab that is more resistant to the movement of expansive soils. Many homes are experiencing failure that is considered unacceptable by the engineering community, building community and homeowners. Recent estimates put the annual cost of foundation repair in the United States in excess of three Billion dollars. The present method eliminates extensive soil pad preparation cost, the high cost of underpinning a structure after it is completely built, and allows the soil in expansive areas to swell without experiencing the adverse effect of foundation movement.  
       SUMMARY OF THE INVENTION  
       [0015]     The present invention provides a structure comprising a poured concrete slab foundation and method for obtaining the structure.  
         [0016]     Briefly the present structure comprises a first component comprising a poured concrete slab on soil, having at least one interior grade beam, grade beams about the periphery of said poured concrete slab, and an array of openings along and adjacent to each said interior grade beam; a second component comprising an array of driven piles in the soil below said interior and preferably below the periphery grade beams; and a third component comprising poured concrete closures in said openings. The present process comprises: preparing a poured concrete slab on soil, having at least one interior grade beam, grade beams about the periphery of said poured concrete slab, and an array of openings along and adjacent to each said interior grade beam; driving an array of pilings in the soil below said interior grade beams adjacent to openings and preferably below said periphery grade beams and pouring concrete closures in said openings.  
         [0017]     The pilings are known in the art and are usually prepared in segments that may or may not be joined by rods, cables, sleeves or the like, which are driven hydraulically into the soil by resistance against the grade beams. By combining a plurality of the segments with the cooperating elements engaged in the ground, a piling is created. The cooperative engagement provides lateral stability of the piling stacking a plurality of such precast one on another. Installation of subsequent segments continues until adequate load capacity and depth are obtained. The pile penetration depth can be easily determined upon completion by simply counting the segments used. This method of installation provides an aligned, concrete underpinning pile of verifiable depth, installed under conditions with almost no clearance.  
         [0018]     The closure of the openings is obtained by use of the cartons, i.e., corrugated cardboard boxes, which prevent the soil from contact with the concrete closures with the cartons collapsing to accommodate the swelling of the soil. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a concrete slab layout according to the present invention showing typical pile locations and knockout box locations for access to install the piling.  
         [0020]      FIG. 2  is a knockout box design that has a keyway, and when stripped leaves a keyway in the slab for future concrete patch.  
         [0021]      FIG. 3  is a doweled knockout box with dowels for tying concrete together when patch is installed.  
         [0022]      FIG. 4  shows typical void carton installation.  
         [0023]      FIG. 5  is typical sleeved plumbing as it extends through the concrete slab. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     After on site soil borings are reviewed by a geotech engineer, the Potential Vertical Rise (P.V.R.) values are determined by the geotech. Based on P.V.R. values, the appropriate size void cartons are to be installed under all beams and throughout the entire concrete mat, except directly under the beams adjacent to the formed excess boxes. After an acceptable concrete curing time, a driven pile system is installed through the opening at the preformed box location. After pilings are driven to refusal or to a predetermined load capacity, the pilings are shimmed with various size spacers.  
         [0025]     Prefabricated knockout boxes to form openings are installed on the interior portion of the slab prior to the pouring of the concrete. These boxes are preferably keywayed or doweled to help prevent slippage of the concrete patch after the piling is installed. After the concrete slab is poured and the concrete has had an acceptable curing time, the forms for the boxes are stripped when all the other concrete forms for the slab are stripped.  
         [0026]     If void cartons are not installed prior to the pouring of the concrete, the below grade waste water lines are preferably sleeved to allow for the raising of the concrete slab without distortion to the below grade waste water lines. This will ensure that the raising of the slab on grade does not alter the proper fall of the plumbing waste water system below the concrete slab floor elevation. All vertical lines extending through the concrete preferably have a PVC sleeve. Plumbing preferably is not run horizontally through the concrete slab and/or concrete grade beams. All lines are preferably run vertically and have a PVC sleeve installed around each plumbing line preventing the vertical lines from being in contact with the concrete slab. The installation of the plumbing sleeves may be eliminated, if the entire slab, including grade beams and mat areas have void cartons installed below the concrete slab prior to the pouring of the concrete slab. The thickness of the voided area is to be based on information taken from soil borings on each pad site. This work is typically done by a geotechnical engineer. The void cartons are to be installed under the entire concrete slab with the exception of the future contact points, i.e., generally the grade beams, where the piles are to support the slab. This will ensure temporary stability of the concrete slab prior to the installation of the cylindrical piling. In a preferred embodiment the slab will be elevated to an acceptable elevation that will prevent the possibility of additional vertical rise due to soil swell. If the plumbing is installed with sleeves and after the foundation is elevated past the potential for vertical rise, the void cartons become unnecessary.  
         [0027]     The process of elevating the slab is done by the excavating of the soil beneath the concrete grade beams by access through the knockout boxes on the interior and by excavating under the exterior grade beams for the installation of the exterior piling. A series of cylindrical driven piling that may consist of concrete, steel, wood or composite material driven to a suitable depth and obtaining the proper pressures by building skin friction that will be capable of supporting the load of the structure after the structure is completely built, are installed. After the installation of the piling, a pile cap is set atop the piling and cylindrical shaped blocks are set atop the pile cap. Then a series of shims are placed between the top cylinders and the concrete grade beam. After the installation of the interior piles and exterior piles, the concrete structure can be elevated past the potential for vertical rise. This is done by hydraulically jacking the slab to a predetermined elevation. This elevation is a predetermined vertical distance based on a calculated value that is determined by a geotechnical engineer&#39;s review of soil borings taken on site.  
         [0028]     Once the pile is positioned, the force of the building or other supported structure must be distributed onto the pile. Generally, the pile diameter is small relative to the downward force of the foundation; therefore, a means for gradually distributing the weight onto the pile is necessary. One way existing in the prior art to provide for such distribution is the use of a pile cap system consisting of different sized concrete blocks. The blocks are arranged to form an upside down or inverse stair-stepped frustum, with the block plane of the smallest surface area being placed on top of the pile. The other blocks are graduated in size upward from the top of the block on the pile to the foundation.  
         [0029]     After the slab is raised to the predetermined elevation, the excavated soil is returned to the holes that were dug for the piling installation, and the knockout boxes are filled with concrete. Void cartons are installed below the concrete patch at the knockout box locations to help prevent vertical rise of the concrete patch. All sleeved plumbing pipes are preferably sealed between the pipe riser and the sleeve.  
         [0030]     The sectional piling provides a completed pile that is equivalent to a one piece precast concrete pile of the same dimensions. The diameter or width of a segment is commonly 6-inches, with the segment being precast of concrete having a minimum compressive strength of 3000-psi or more. Normally the segments will have a cylindrical form. A rectangular or other cross section may be used. A structural adhesive, typically a 2-component epoxy, may be used to bond the concrete segments one to another during their assembly in the ground as pile. Normally the weight of the structure will be enough to maintain the contact between the segments.  
         [0031]     Installation equipment typically comprises incidental hand tools to excavate holes and hydraulic jacks with an electric pump. Because the precast components and equipment are small in nature, the underpinning operations usually require only limited clearance, or head room, and support locations will be beneath the perimeter and interior of a building. The dimensions, reinforcing requirements and location of the pile are site specific, and depend primarily on the soil conditions and structural loads needing to be supported.  
         [0032]     The process of installing piles may include steps of removing a volume of earth from beneath a portion of a structure, positioning a first pile segment below said portion of said structure, placing a hydraulic ram, jack, or similar jacking device between said first pile segment and said portion of said structure, driving a first pile segment a distance into unexcavated earth. The first pile segment has an end extending out of the earth to seat said second pile segment onto which is driven another distance into the earth. In such a procedure, there are several ways to construct and position a pile. Regardless of the manner in which a pile is constructed, however, most are made primarily of concrete and have an overall cylindrical shape with a length varying according to the soil type and weight of the structure.  
         [0033]     In  FIG. 1  the layout of slab foundation  1  formed according to the present process is depicted in schematic format. Preferably void cartons are positioned below entire foundation, with the exception of the knockout boxes  18  and the portions of the grade beams (perimeter  10  and interior  12 ) where the piles  16  are installed. Pilings can be easily installed on the perimeter as desired. This isolates the foundation from ground heave until the piles are installed and will continue to provide better stability against ground heave during the life of the foundation. The void cartons may be positioned over the entire footprint of the foundation, since they do not present any substantial barrier to installation of pilings. However, as a matter of economy, which is principal aspect of the present invention, reducing the amount of excavation by not installing void cartons where the piles are to be located, will reduce labor cost. The perimeter pilings  14  are installed from the outside access and the interior piling  16  are installed though the knockout boxes using any of the pile installations systems presently used in after market foundation repair.  
         [0034]      FIG. 2  show a knockout box  18  with the frame members  20  in place on the ground  25  with dowels  22  (such as metal rebar) extending from area of the foundation pad (when poured) into the open knockout box. The frame members will be removed when the other foundation frame members (not shown) are removed after cure of the poured foundation. After a piling is positioned under an adjacent interior beam (not shown) a void carton (not shown) in placed in the knockout box below the dowels and concrete filled to the level of the foundation pad.  
         [0035]      FIG. 3  show a knockout box  18  with the frame members  21  in place on the ground  25  with keyway elements  23  extending from open knockout box into the area of the foundation pad (when poured). The frame members will be removed when the other foundation frame members (not shown) are removed after cure of the poured foundation. After a piling is positioned under an adjacent interior beam (not shown) a void carton (not shown) in placed in the knockout box below the impression of the keyway in the foundation when poured and concrete filled to the level of the foundation pad.  
         [0036]     FIG. illustrates a typical foundation configuration at a perimeter grade beam  10 , where there is no piling installed below the grade beam and no knockout box. The grade beam  10  and the foundation mat  26  are positioned in the ground  25  and void cartons  24  are position below each.  
         [0037]      FIG. 5  is a representation of a plumbing sleeve  30 , through the foundation pad  26  to surround the riser  28 , but not tightly engage the riser, which isolates the riser and the in ground plumbing  32  from the movement of the foundation.