Abstract:
A plurality of precast ground bearing foundation pads are provided at spaced-apart locations. Precast wall sections span between and bear upon the pads, each pad having a groove in its upper surface for receiving and holding a base of the wall section. Separate foundation holes may be excavated for each pad, the holes are backfilled to fix the pads in position.

Description:
RELATED APPLICATIONS  
         [0001]    This application claims the benefit of the New Zealand patent application No. 511899 filed May 23, 2001.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to the prefabrication of foundations, and more particularly, but not by way of limitation, to prefabricated foundations to support residential and commercial buildings.  
           [0004]    2. Description of the Related Art  
           [0005]    In typical current construction practice, foundations for buildings are formed by excavating a foundation hole, assembling forms within the hole to effectively form a mould, pouring concrete within the assembled forms, and then removing the forms when the concrete has set. The foundation is then left standing in the foundation hole, which is backfilled around the exterior of the foundation. The remainder of the building is then constructed atop the poured foundation. As a result of this process, construction progress is highly dependent on the timely completion of the foundation. This can lead to difficulties in areas where soil conditions delay or hinder the digging of the foundation hole, and where the climate is not agreeable to pouring of concrete, owing to rain in particular.  
           [0006]    Further difficulties with properly forming a foundation are inherent in the pouring process. Because foundation walls must be poured within vertically-oriented forms, the concrete mix must have a low “slump” value, that is it has to be sufficiently fluid to fill out all comers, prevent voids, etc. However, in order for the concrete mix to reach this low slump value a substantial amount of water must be used in the concrete mix. This results in weaker, lower-density concrete, with greater permeability to water after setting occurs. Further, a watery concrete mix results in longer concrete setting/curing times. This further slows building construction because backfilling against a newly-poured foundation before it slows building construction because backfilling against a newly-poured foundation before it is fully set may cause the foundation walls to collapse, or may crack them to later allow water to enter the foundation. Other drawbacks associated with foundations poured on sire include the difficulty in obtaining a good quality exposed surface due to poor workmanship in constructing the form. Ensuring correct placement of reinforcing steel, particularly to give the correct concrete cover, is also problematic  
           [0007]    Precast concrete foundations walls have been proposed to overcome some of the problems associated with cast in situ foundations walls. The manufacture of precast wall panels in a factory avoids the problems associated onsite quality control and the vagaries of the weather. Once a crushed gravel base for the precast sections is in place, the precast system can be erected very quickly. The problem associated with this method of construction however is the accuracy required in forming the base of crushed metal. Due to the narrow bearing area along the base of the wall, a considerably depth of crushed aggregate has to be provided. Precise preparation of the crushed metal is required in order to support the precast walls upon a flat and true surface for the full length of the foundations.  
           [0008]    U.S. Pat. No. 4,125,980 describes a foundation which includes cast insitu concrete footings provided at spaced apart locations around the perimeter of the building to be erected. Precast reinforced concrete beams are set in place with each beam bearing on adjacent footings. To join the beams and to fasten them to the footing adjacent ends of each beam are formed with a keyway and a concrete column is poured which extends through this keyway and hardens to secure the beams in place. The disadvantage of this method of constructions is it still relies upon concrete which is poured on site and which is vulnerable to weather, seasonal and climate limitations and the general human errors and lack of precision associated with this type of construction.  
         SUMMARY OF THE INVENTION  
         [0009]    It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice. Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.  
           [0010]    According to one aspect of the present invention there is provided a foundation assembly, including at least two precast ground bearing foundation pads at spaced-apart locations, and at least one precast wall section spanning between and bearing upon said pads, wherein each pad has means for receiving a base of said wall section.  
           [0011]    The foundation assembly may form part of a building construction, a retaining wall or a fence or the like. Henceforth reference will be made to building construction, however this should not be seen as limiting and the variations described will apply equally to other like constructions.  
           [0012]    Preferably each precast wall and pad includes a cast section which is formed of concrete or other cementitious materials. Alternatively other materials such as composite materials may be employed.  
           [0013]    In a building construction the wall sections extend generally vertically from the pads, above the ground level and preferably up to approximately the floor level. Alternatively, the walls may extend to integrally form the sides of a building. The walls include surfaces adapted to support wall or floor structures, including brick and block walls, and timber framed walls and floors.  
           [0014]    Preferably adjacent wall sections are abutted. Abutting faces may be shaped for inter-engagement. At joints between wall sections a sealant or adhesive may be applied, or an intermediate sealing element may be provided.  
           [0015]    One or more intermediate foundation pads may be provided between two pads spanned by a wall section. All corners in a wall section a re preferably supported by a pad.  
           [0016]    Preferably each said pad is laterally fixed by fill material surrounding the sides of the pad. The fill material is self-compacting granular material, crushed metal, other aggregate or concrete compacted around the sides of the pad.  
           [0017]    Preferably the said means for holding the base of the wall includes at least one groove into which the base is received. Preferably the groove has parallel vertical faces adapted to engage corresponding vertical faces of the wall. The groove may be lined with a channel member cast into the top of the pad. The groove is aligned with the longitudinal axis of the wall, thereby acting to fix the base laterally.  
           [0018]    Optionally other means of holding the base to the wall may be provided, including brackets and fasteners of a known type. Optionally the means for holding the base of the wall may include means for performing small adjustments of the position of the wall  40  relative to the pad  1 .  
           [0019]    Preferably each said wall section is laterally fixed by fill material on either side of the wall section.  
           [0020]    Preferably adjacent wall sections abut to form a substantially continuous ring foundation. The ring foundation may surround substantially the whole of a building or alternatively only apart thereof.  
           [0021]    Preferably the said wall sections are topped by a cast in situ concrete floor slab. Alternatively the said wall sections support a floor of joist type construction, prefabricated construction or other construction.  
           [0022]    Optionally, the wall sections may include reinforcing elements projecting from one or more faces thereof. These reinforcing elements may include a helical wire coil or substantially straight rods.  
           [0023]    The inside faces of adjacent wall sections may be joined by an angle bracket fixed to fasteners cast into the said inner faces. Alternatively, the upper faces of adjacent wall sections may be joined by a bracket having a slot for adjusting the joint opening.  
           [0024]    Preferably the pad includes a pad fixture and the wall includes a wall fixture, the pad fixture and wall fixture being adapted for engagement with a lever for manual manipulation of the position of the wall relative to the pad. Most preferably, the pad fixture is a V-shaped pad recess formed in an upper surface of the pad in a medial section of the groove. Most preferably, the wall fixture is a wall recess in the vertical face of the wall, having a pair of opposed walls elongated in the vertical direction.  
           [0025]    A cast in situ foundation strip may extend between two adjacent pads. The strip may be cast into permanent or temporary formwork or directly into the open excavated trench.  
           [0026]    A pad may alternatively be supported upon and fixed to a pile footing. Preferably the pad is fixed to the pile by an adhesive, such as grout. Preferably, the pad includes an aperture having a shoulder for abutment against an end of the pile footing and a smaller section opening into the base of the groove adapted for the injection of adhesive therethrough.  
           [0027]    According to another aspect of the present invention there is provided a method of constructing a foundation assembly substantially as described above, the method including the steps:  
           [0028]    a) lining the base of a pad excavation with a bed of self-compacting granular material;  
           [0029]    b) placing one pad on the bed of compacted material;  
           [0030]    c) surrounding the pad with fill material to set it in position, and  
           [0031]    d) placing the wall section upon the pad.  
           [0032]    Alternatively the base of a pad excavation may be lined with crushed aggregate compacted in situ or optionally with concrete. The method may be repeated for each pad in a construction.  
           [0033]    Preferably the sites of the pad excavations are deeper than any excavation therebetween.  
           [0034]    According to another aspect of the present invention there is provided a method substantially as described above including the further subsequent step:  
           [0035]    e) surrounding the sides of the said wall section with fill material.  
           [0036]    According to another aspect of the present invention there is provided a precast concrete foundation pad with a substantially planar ground bearing base, sides, and a groove extending the full width of a top of the pad, the groove having substantially vertical sides adapted to receive and hold a precast wall section.  
           [0037]    The size of the pads and the number of the pads is chosen in accordance with a known manner depending upon the bearing strength of the soil. The sides may be tapered or straight. Alternatively a pad may have three or more sides, or may be circular or oval or the like.  
           [0038]    One preferred embodiment of the pad has a rectangular outline in plan view and the top includes two grooves of the same depth, the longitudinal axes of which intersect at right angles.  
           [0039]    This invention provides a prefabricated foundation system which is effective and versatile in operational use, and allows foundations to be constructed more quickly than has previously been possible. The length of time during which foundation excavations are open and therefore vulnerable to the weather is greatly reduced, with significant time savings for building construction. This invention satisfies a need, particularly in low cost housing, for a durable concrete foundation capable of being erected by taking advantage of the economy of precast units and also having an inexpensive system for assembling the precast units into a completed structure. The components themselves may be economically constructed and have an overall simple design which minimizes manufacturing costs and maximizes performance. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0040]    Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which:  
         [0041]    [0041]FIG. 1 is a pictorial view of a foundation assembly of the present invention;  
         [0042]    [0042]FIGS. 2 a  and  2   b  are details of a joint of FIG. 1;  
         [0043]    [0043]FIG. 3 is a pictorial view of a join between two wall sections of a foundation assembly of the present invention;  
         [0044]    [0044]FIGS. 4 a - 4   d  illustrate four sequential stages in the construction of the foundation assembly of FIG. 1;  
         [0045]    [0045]FIGS. 5 a - 5   f  are sectional elevations of a foundation assembly of the present invention adapted for different floor and wall constructions;  
         [0046]    [0046]FIGS. 6 a - 6   f  are pictorial views of five different embodiments of a foundation pad of the present invention;  
         [0047]    [0047]FIG. 7 is a pictorial view a part of a wall and a pad of the present invention;  
         [0048]    [0048]FIG. 8 is a plan view of a continuous ring foundation of a building employing the foundation assembly of the present invention;  
         [0049]    [0049]FIG. 9 is a pictorial view of a foundation assembly of the present invention showing a tapered wall section, and  
         [0050]    [0050]FIG. 10 is a plan view of a continuous ring foundation incorporating two different wall elements;  
         [0051]    [0051]FIG. 11 is a pictorial view of a foundation system of the present invention including a cast in situ strip footing;  
         [0052]    [0052]FIG. 12 is a pictorial view a part of a wall and a pad of the present invention fixed to a pile foundation;  
         [0053]    [0053]FIG. 13 is a sectional view through the pad of FIG. 12; and  
         [0054]    [0054]FIG. 14 a  and  14   b  are pictorial views of the intersection of multiple walls in a foundation assembly of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0055]    Referring to FIG. 1 of the drawings, a foundation assembly of the present invention includes two spaced apart foundation pads  1   a ,  1   b . The designations  1   a ,  1   b  etc. refer to different embodiments of a general foundation pad  1  according to the present invention (a like method of designation is also used in referring to other components described herein). The foundation pads  1  are formed from precast reinforced concrete and include a generally planar ground engaging base  2 , sides  4  and a top  3 .  
         [0056]    Spanning between the foundation pads  1   a ,  1   b  is a precast concrete wall section  40   a  having substantially parallel vertical sides  41 ,  42  and upper and lower edges  43  and  44  respectively.  
         [0057]    Formed in the top  3  of each foundation pad  1  are grooves  30  for receiving and holding the wall section  40 , the bottom edge  44  of which bears upon the foundation pads  1 . Two walls  40   a ,  40   b  intersect at approximately right angles and are supported upon a comer pad  1   b . A bevel joint  45  (shown in detail in FIG. 2) is provided at the intersection.  
         [0058]    Referring to FIG. 2 a , the bevel joint  45  includes an angle bracket  47  on the internal faces  42  between the walls  40   a ,  40   b . The angle bracket  47  is fastened to the walls  40   a ,  40   b  by means of cast in fasteners  48 . A seal  46  is provided for water proofing the joint  45 . Although formed in modular sections the present foundation assembly can actually provide greater resistance to water entry than “single-piece” poured foundations. Poured foundations are highly susceptible to cracking somewhere along their lengths, whereas the walls  40  of the present invention are smaller and less susceptible to stress cracking. Further, the walls  40  will alleviate stress by flexing at the joints  45  between abutting modules. Provided these joints  45  have been waterproofed by means of a sealant/adhesive, water is unlikely to enter.  
         [0059]    [0059]FIG. 2 b  illustrates an alternative square butt joint detail where the fastenings connecting the wall sections are only fixed temporarily during construction and which have the advantage of being reusable. The upper edges of the wall sections  40   a ,  40   b  are joined at the joint by a bracket fixed by fasteners  48 ,  48 ′. One end of the bracket  147  is slotted to provide adjustment for opening and closing the joint. Preferably the fasteners  48 ,  48 ′ are bolts which engage with female threaded inserts (not shown) molded into the upper edges of the wall sections  40   a ,  40   b.    
         [0060]    [0060]FIG. 3 illustrates additional brackets  47  and tie strips  49  which may be employed for connecting the walls  40  and for fastening the walls  40  to the pads  1 . Due to the tongue- and-groove type connection between the walls  40  and pads  1 , the brackets  47  connecting them provide resistance to longitudinal (with respect to the longitudinal axis of the wall) or uplift loads due to wind or earthquake.  
         [0061]    The method of constructing the foundation assembly of the present invention is illustrated. with reference to FIG. 4 a  to  4   d.  FIG. 4 a  illustrates an excavation  54  for the installation of a comer type foundation pad  1   b . The excavation  54  for the foundation pad is made to a depth  51  below the surrounding ground level  50 . The excavation  55  is provided between pad excavations  54  to accommodate the base of the wall (not shown) and need only be of a lower depth  53 . Next the base of the excavation  54  is lined with a bed of self-compacting granular material  59  which is carefully levelled.  
         [0062]    Next the foundation pad  1   b  is placed upon the bed of compacted material  59  (FIG. 4 b ) and it is then surrounded by compacted fill material  57  to set it in position. (FIG. 4 c ). The wall sections  40   a ,  40   b  are then placed upon the foundation pad  1   b  e.g. by a crane. Shims (not shown) may be used to provide any adjustment required in the position of the walls  40 . Any gap in the connection between the pads  1  and the wall  40  may be filled with grouting, cement or similar load bearing filler. Referring to FIG. 4 d,  once the walls  40   a ,  40   b  have been finally positioned and the brackets  47  or fastener strips  49  are fixed, backfill  58  may be placed on either side of the wall  40   a ,  40   b  and compacted ensuring that material is placed beneath the bottom edge  44  to provide some intermediate support for the wall  40 .  
         [0063]    The walls  40  may include varying constructional details depending upon the proposed building constructions. A selection of details for different walls  40 ,  140 ,  240 ,  340 ,  440 ,  540  are illustrated in FIGS. 5 a - 5   f.  The wall section  40  (FIG. 5 a ) includes a steel reinforcing rod  60  which protrudes from an upper part of the inner wall  64 . The wall  40  supports a cast insitu floor slab  63  and has a recessed edge  61  provided along with front face  62  of the wall  40  to support brick cladding  65 .  
         [0064]    The wall section  140  (illustrated in FIG. 5 b ) includes a recessed edge  68  which locates the cast insitu floor slab  63 . FIG. 5 c  illustrates a wall section  240 , which like wall section  140  includes a horizontal starter rod  60 , but has an additional starter rod  69  to extend inside the lower blocks  70  of a concrete masonry block wall. FIG. 5 d  illustrates a wall section  340  adapted for use with a timber flooring system having a recess  71  adapted to support a timber stringer  72 . FIGS. 5 e  and  5   f  show walls  440  and  540  respectively without recessed edges for locating the floor slab  63 . Wall  440  (FIG. 5 e ) is reinforced with steel wire mesh  73  and to key into the slab  60  a helical coil of steel reinforcing wire  74  is cast into the inner face of the wall. Openings (not shown) may be provided in the walls  40  for services, ventilation etc.  
         [0065]    In a typical pad  1 , two walls  40  will be joined. FIG. 6 a  illustrates a comer pad  1   b  for joining two walls (not shown) at right angles. The L shaped groove  30  in the top  3  has vertical sides  73  supporting each of the wall sections  40 .  
         [0066]    [0066]FIG. 6 d  illustrates a pad  1   a  having a straight groove  30  which can be used either for joining two walls  40  or at an intermediate position between the ends of a wall  40 . FIG. 6 c  shows a pad  1   c  having an angle shaped groove  30 . FIG. 6 b  and  6   e  illustrate pads  1   d  and  1   e  having a T shaped groove  30  and cross shaped grooves  30  respectively. In the pads  1   a - 1   e  the grooves  30  extend medially across the upper face  3 . FIG. 6 f  illustrates a groove  30  formed closer to an edge  4  of the pad  1   f,  in order to allow the wall  40  to be positioned close to a boundary line  74 , for example, without the pad  1   f  encroaching beyond the boundary.  
         [0067]    Another feature of the pads and the walls is illustrated in FIG. 7, which shows the means by which the wall  40  may be manipulated during construction relative to the pad  1   b . The drawing illustrates a comer pad  1   b  having V-section recesses  91  formed in the upper face  3  thereof, the recesses being adapted to engage with a lever  93  which is also provided with lugs  94  for engagement with recesses  92  formed in the vertical face of the wall  40 . In the preferred embodiment illustrated, the pad recesses  91  are formed in a medial section of each of the two perpendicular sections of the groove  30  having their axis generally perpendicular to the axis of the adjacent groove section. The pad recesses  91  are shaped to engage with a pointed tip  95  of the lever  93 . The wall recess  92  has a pair of opposed walls elongated in the vertical direction and has a depth to accommodate the length of the lugs  94 . It will be appreciated that the recesses  91  and  92  may be positioned so that the corresponding edge of the pad  1  or wall  40  may be engaged with the lever  93 . For example, the wall recess  92  could be located directly above the edge of the pad  1   b , allowing the lever  93  to gain purchase against the side of the footing pad  1 .  
         [0068]    As illustrated in FIG. 8, in constructing a foundation for a building  100 , foundation pads  1  are provided at each corner of the building  100 . In the preferred embodiment this ring beam foundation is topped by a cast insitu concrete floor slab  63  which assists in tying together the separate wall elements  40 .  
         [0069]    It will be appreciated by those skilled in the art that many different variations of the shape and dimensions of both the walls  40  and the pads  1  are contemplated by the present invention. Illustrative of some of these variations are a tapered wall  40  (FIG. 9) to account for a sloped contour on the ground. Although the walls are generally panel shaped, optionally, ribbing (not shown) may also be included.  
         [0070]    [0070]FIG. 10 illustrates the construction of a simple building such as a garage, workshop or the like. The corner details X and Y refer to the helical coil reinforcement and horizontal starter rod arrangements shown in FIGS. 5 e  and  5   f  respectively, which may or may not be combined in a single structure such as this. In lightweight buildings a single pad  1  at each corner of the foundation is sufficient, depending upon the bearing strength of the soil. The modular nature of these buildings allows the wall and roof construction to be started as soon as the foundations are erected, and before backfilling or floor slab installation. In this case this foundation system offers a further advantage of allowing the floor slab to be poured in a substantially enclosed space, letting construction to proceed without delay caused by inclement weather.  
         [0071]    [0071]FIG. 11 illustrates the use of the present foundation system in a manner allowing it to be adapted to accommodate either poor ground conditions or higher loadings by providing a continuous strip footing. The ground is prepared to receive a concrete strip cast in situ between the two foundation pads  1  which supports the intermediate part of the wall  40 . The wall  40  is positioned and held in the pads  1 , formwork  80  is run on either side between the pads  1  with reinforcing  60  placed as is desired, before pouring the intermediate section. Optionally the perimeter of a building may be completed in this manner.  
         [0072]    [0072]FIGS. 12 and 13 illustrate an alternative to the above-described method to accommodate either poor ground conditions or higher loadings. In this embodiment a pile footing  101  is provided to support the foundation walls  40 , with a pad  1  connected therebetween. Preferably an adhesive, such as grout is used to fix the pad  1  to the top of the pile  101 , once it has been located.  
         [0073]    In the embodiment illustrated in FIG. 13, the pad  1  includes an aperture having a shoulder  75  for abutment against the end of the pile  101  and a smaller section  76  opening into the base of the groove  30 . Before placing the wall section  40 , grout may be injected into the aperture to fasten the pad  1  and the pile  101 .  
         [0074]    [0074]FIGS. 14 a  and  14   b  show the manner in which intersections between walls  40  may be accommodated by different pads  1 d,  1 e. The walls  40  will generally have the same thickness as a standard concrete foundation wall, e.g., 150-300 mm, and may be configured to have any desired height and length. The wall  40  dimensions may vary widely to suit the particular application. It is expected that in most applications, adjacent walls  40  will have the same height and width, but variations in length between different walls  40  will be relatively common.  
         [0075]    Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.