AUSTRALIA Patents Act 1990 SuperSlab Tech Pty Ltd COMPLETE SPECIFICATION Invention Title: Apparatus for creating a void beneath a suspended structural concrete slab The invention is described in the following statement: 2 Related Applications The present application is related to Australian Patent Application Nos. 2007203032 and 2010246376, the entire disclosures of which are incorporated herein by way of reference. 5 Field of the Invention The present invention relates to an apparatus for creating a void beneath a suspended structural concrete slab and in particular to an apparatus for cieating a void beneath a suspended structural concrete slab of a building/construction such that the 10 building/construction is suspended above the ground and is able to withstand changes in the level of the underlying ground support. Background Ar Buildings, such as residential homes or commercial buildings generally rely 15 upon a solid footing upon which to support the considerable weight of the structure. The footing generally provides a flat and level base upon which the building is supported, with the base being in communication with the underlying ground surface. Many modern buildings are built upon a flat, concrete slab that provides both a base for the structure as well as the bottom floor for the building. The cocrete is typically 20 placed over a prepared ground surface and is shaped to the desired ditnensidtihs to form the footings of the building. This may be achieved through laying pre-cast comporienis of concrete, or through pouring wet concrete into a mould and allowing the concrde to set in position. Typically such concrete slabs consist of a system of structurally engineered concrete beams and platforms which together form what is collectively 25 referred to as a slab. A common problem with concrete slabs supported on a ground surface is that large ardas of land available for residential development have soil profiles with high clay conerit. Such soil profiles are not considered stable, as the surface level of the soil can change as the moisture content of the soil changes. This is due to the volume of the 30 soil being directly dependent upon the soil's moisture content. In particular, as the moisture content of the soil increases, the volume of the soil increases, restilting in the surface level of the soil changing. Such a phenomena causes uplifting of a conc-ete slab that may be supported on the surface of the soil. This uplifting of soil is commonly referred to as the concrete slab being considered to have "heaved". With 35 such soils, when their moisture content reduces, the soil reduces (shrinks or settles) in volume.
3 Heaving and settling of soil due to moisture content change therein tends to occur at varying rates across the surface plane of the soil. This variance is termed differential movement. As a concrete slab being supported on the surface of such soil will heave and settle accordingly, this differential movement can result in a concrete 5 slab supported on such a soil surface experiencing a variety of loading forces over the life of a building construction. The factors contributing to variations in soil moisture content which generates such concrete slab movements are various and complex. Some common factors include: natural moisture variations due to seasonal considerations such as wet and dry 10 seasons; soil drying due to trees growing or being introduced into a zone of influence of the soil; soil wetting due to the removal of trees and other related flora such that previously drier soils re-hydrate resulting in the phenomena of "rebound" occurring in the soil; garden watering (or lack thereof) by owners/occupiers of a subject site; or a combination of any of these sources- Any or all of these factors can significantly alter 15 the soil moisture content resulting in a concrete slab deflecting or becoming damaged. This can result in damage to the super structure supported on the slab, such as a residential dwelling or the like, requiring time consuming and expensive corrective action. Typically, soil moisture content is not consistent and may vary across regions, 20 resulting in further differential shrinking/swelling of the soil. Histdrically, construction areas have been chosen to avoid soils having a high clay content to reduce the occurrence of soil heave. However, as populations increase, more and more land having such high clay content soil is being used for development. In this regard, ardtts which have previously been avoided such as beach/river frontages; steeply sloping 25 hinterland areas beyond the coastlines; and the grazing plains (some of which are flood prone) which surround most cities and towns are increasingly becoming the site for a variety of constructions and developments that have previously been considered unsuitable for such a soil base. A number of methods have been proposed to address the soil heave phenomena 30 and to prevent highly expansive soils from damaging the structures supported on such soil. Typically, these methods are employed prior to construction and rely upon chemical treatment of the soil; engineered fill and compaction of the soil; and/or the formation of a void space beneath the concrete slab to accommodate expansion of the soil into these voids without damaging the structure.
4 Most void systems previously proposed have been arranged such that the beams of the concrete slab are placed between the void forming elements, the beam regions of the concrete slab do not have a void space and hence are more susceptible to soil heave. Any discussion of documents, acts, materials, devices, articles or the like which 5 has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application. 10 Summary of the Invention Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. 15 There is disclosed herein an apparatus for creating a void beneath a structural concrete slab, comprising: a body having a closed first end adapted to support at least a portion of the concrete slab during curing and a second end adapted to contact a ground surface, wherein said body has sidewalls around a periphery thereof for forming sides of beam 20 portions of the concrete slab, wherein at least one cavity is provided in the body, the at least one cavity extending at least partially from said second end toward said first end; and a plurality of supporting posts located in the cavity and extending from the first end to the second end of the body, the posts being solid and formed in unitary one piece 25 construction with the body, each post having a proximal end adjacent the first end of the body and a distal end adapted to contact the ground surface to provide support to the first end, wherein the posts are deformable such that a rise of the ground surface into the cavity will cause deflection of the posts. The posts may be regularly spaced within the cavity. 30 A transverse cross section through each of the posts may have a first major dimension that is less than half of a width of the cavity and a second major dimension that is less than half a length of the cavity, and the posts may be configured in a spaced apart array within the cavity, with spaces being provided between the posts both in a first direction corresponding to the width of the cavity and in a second direction 35 corresponding to the length of the cavity.
5 The body may be sacrificial, being formed to be capable of withstanding forces placed upon it during formation of the structural concrete slab and being arranged to collapse under a force of ground movement occurring after the slab is formed. A sum of the transverse cross sectional areas of the posts may be less than half a 5 corresponding transverse cross sectional area of the cavity. Throughout this specification, the term "post" is to be understood as meaning an elongate projection, which may or may not have a constant transverse cross section. Brief Description of the Drawings 10 By way of example only, the invention is now described with reference to the accompanying drawings: Fig. I is a perspective view of the void forming and suspension arrangement of an embodiment in accordance with the present disclosure; Fig. 2 is a cross sectional side view of the void forming and suspension 15 arrangement of Fig. 1, supporting a concrete slab; Fig. 3 is a plan view of the slab of Fig. 2; Fig. 4 is a perspective view of an embodiment of a spacer void forming element of the void forming arrangement of Fig. 1; Fig. 5 shows a plan view of a second embodiment of a spacer void forming 20 element of the void forming arrangement of Fig. 1; Fig. 6 shows an elevation view of the embodiment of a spacer void forming element of Fig. 5 with a first height; Fig. 7 shows an elevation view of the embodiment of a spacer void forming element of Fig. 5 with a second height; 25 Fig. 8 shows (a) plan, (b) elevation and (c) end elevation views of an embodiment of a shallow void forming element of the void forming arrangement of Fig. 1; Fig. 9a shows a underside perspective view of an alternative embodiment of the void forming elements of Figs. 4-7, and Fig. 9b shows a plurality of the void forming 30 elements of Fig. 9a grouped together in abutting relationship; Figs, 10a and 10b show underside perspective and cross-sectional views, respectively, of a further alternative embodiment of the void forming elements of Figs. 4-7; and Fig. 11 shows cross sectional side views of further embodiments of a void 35 forming and suspension arrangement in accordance with the present disclosure, supporting a concrete slab.
6 Detailed Descrintion of an Exemplary Embodiment of the Present Inyntion A void forming and suspension system 10 in accordance with one embodiment of the present invention is shown in Fig. 1 5 The void forming and suspension system tO generally consists of a plurality of void forming elements 12, 16 arranged to extend over a ground surface 22 upon which the building is to be constructed. As will become more apparent in the following description, the void forming system 10 functions to act as an interface between the ground surface 22 and a concrete slab 20 of the building to be constructed, 10 Prior to positioning the void forming system as shown in Fig. 1, a plurality of load bearing compression and tension piles 14 are driven, drilled, jacked, tied or otherwise fixed into the deeper soil or rock of high bearing capacity to provide stability to the structure which is to be built. The piles 14 may be in a variety of forms, such as screw piles which communicate directly with the load bearing ground beneath the 15 ground surface 22. The piles 14 perform in both tension and compression and are raised above the ground surface to a predetermined height, In this regard, the piles are arranged in a grid to form a consistent and level loading region above Arourid upon which to found the beams of the finished concrete slab. The depth to which the piles 14 are installed is determined in relation to Where 20 they will achieve the engineered and designed bearing capacity for the said building/construction. The installed height of each pile 14 above ground will allow the end of the piles 14 to penetrate to an engineered depth into the finished beams of the concrete slab above. The piles 14 are subsequently structurally connected to the concrete slab within the beam. it will be appreciated that the size and shape of the slab 25 can be readily adapted to suit the size and shape of the building to be constructed. As such, the placement location and number of piles 14 utilised is variable, though based on the relevant modular system engineered design for that project. Following the positioning of the piles 14 in accordance with the design of the structure to be built, void forming elements 12 are positioned over and around the piles 30 14. The void forming elements 12 are in the form of elongate shallow members which are designed to effectively absorb extreme ground movement as well as allow the piles 14 to pass therethrough. As the void forming elements 12 extend along the piles 14, they are typically arranged in parallel rows in accordance with the specific design of the structure to be built, It will be appreciated that the arrangement as shown in Figs. 1 35 to 3 represents a substantially rectangular footing wherein the piles are regularly spaced and positioned in rows and hence the void forming elements 12 extend in rows, 7 however it will be appreciated that the footing structure may vary in accordance with the specific design of the building to be constructed. Between each of the rows of shallow void forming elements 12, there are provided spacer void forming elements 16. The spacer void forming elements 16 are in 5 the form of elongate void former structures, such as but not limited to, foam plastic elements as discussed above. The spacer void forming elements 16 extend between each of the shallow void forming elements 12 as shown to provide an additional surface, elevated from the ground surface, offering a holistic void forming body upon which the concrete slab (platform regions and beams) can be placed. In this regard, the 10 platform and beam regions of the concrete slab are supported upon the spacer void forming elements 16 and the shallow void forming elements 12 and are suspended from the ground surface upon placement. It will be appreciated that prior to setting and positioning the void forming system 10 of Fig. 1, the area upon which the void forming system is placed is prepared. 15 Such preparation typically comprises excavating the site to form a level surface upon which the concrete is to be placed. Trenches can also be dug to position deep edge bearns and the like to define the perimeter of the foundation to enable the piles 14 to be positioned as discussed above. A vapour barrier/retarder may also be laid upon the soil surface, below the shallow void forming elements 12 and spacer void forming elements 20 16 to prevent the transmission of moisture upward through the slab from the soil below. Once this has been done the void forming elements 12, 16 can be positioned as shown in Fig. 1, for placement of the concrete. As the spacer void forming elements 16 and the shallow void forming elements 12 are made from a foam or polystyrene material, such as a closed cell expanded 25 polystyrene (BPS). they can be readily shaped or cut to fit around plumbing pipes and the like, through the use of a hand or power saw. Generally, this may not be necessary as the spacer void forming elements 16 and shallow void forming elements 12 can be custom made and delivered to the building site to suit the building plans provided. It will be appreciated that whilst the void forming elements 12, 16 of one embodiment of 30 the invention are made from a foam or polystyrene material, the void forming elements may be made in a variety of shapes and from a variety of materials to enable the void forming system 10 to perform its function, as will be appreciated below. Prior to placement of the concrete slab 20, reinforcing mesh and bar 18 (as shown in Fig. 2) may be placed over the void forming elements 12, 16 to further 35 reinforce the slab 20. Such a mesh material may be particularly applicable if the concrete is to be poured over the void forming elements 12, 16 to form the slab 20. As 8 is clearly evident in Fig. 2, the slab 20 is fully supported above the surface of the soil 22 by the void forming elements 12, 16 and piles 14, thereby completely isolating the slab 20 from the ground soil 22, In this regard, following setting/positioning of the slab 20 and construction of a building over the slab 20, the slab is suspended above the 5 ground surface 22, with the load of the structure being supported by the piles 14 which are in turn supported by the deeper soil or rock of high bearing capacity. It will be appreciated that in this arrangement, the piles 14 have a direct/positive engagement with the slab 20 and the ground, thereby offering load bearing capacity ftr the concrete slab in both tension and compression. The engagement will typically be in the form of 10 a wider portion located in the upper part of the pile such that the concrete formed over the pile surrounds and engages the wider portion and a narrower portion beneath it. Preferably the wider portion comprises a rod or bar 15 extending horizontally through a hole in a vertical portion of the pile located above the lower extremity of the structural slab, Preferably also the piles are located in beam portions 13 of the structural slAb and 15 the rod or bar 15 extends longitudinally of the beam portions. Fig. 3 shows a plan view of one such slab arrangement 20 where the shallow void forming elements 12 are arranged to form two internal parallel beanis whicb extend the length of the slab 20. Perimeter beams 24 are also formed by placement of shallow void forming elements 12 about the perimeter of the site such that the parallel 20 beams work in conjunction with the perimeter beams 24 to form a grid arrangenient upon which the slab 20 is supported, separate from the ground surface. It will be appreciated that the size and shape of the slab 20 can be readily adapted to suit the sie and shape of the building to be constructed. As such, the void forming and suspension system 10 is a modular arrangement that can be easily assembled to accommodate a 25 variety of sized and shaped slabs. rn this regard, a variety of sizes are provided in both the void forming elements 12, 16 to accommodate differing dimensions of the slab design and positions and lengths of the piles 14 to accommodate varying depths of soil penetrated to achieve the appropriate bearing capacities required. Referring to Fig. 4. one embodiment of the structure of the spacer void forming 30 element 16 is shown. The void forming element 16 is in the form of a box-like element having four vertical side surfaces 26 and a top surface 28. The surfaces 26, 28 of the void forming element 16 are configured to interface with the concrete slab 20 in the manner as shown in Fig. 2. The underside 30 of the void forming element 16, namely the side which is supported on the ground surface 22, is open thereby providing a 35 cavity within the void forming element 16. The cavity is defined by the inner walls of 9 the surfaces 26, 28, and in the embodiment as shown in Fig. 4, represents a substantially rectangular space. A plurality of strut members, in the form of posts 32, are provided within the cavity and extend from the inner surface of the top surface 28 to the ground surface 22 5 when the void forming element 16 is positioned thereon for use. The posts 32 support the top surface 28 of the void forming element 16 along its length such that the top surface 28 is able to support the load of the reinforced concrete during placement of the slab 20, as well as the load of workers or machinery used during the placement process. In this regard, the shape of the posts 32 and their location within the cavity defines the 10 strength of the void forming element. It will be appreciated that the arrangement and shape of the posts 32 can be altered in accordance to the specific construction. Such an arrangement of posts 32 provides structural integrity and enables the void forming elements 12, 16 to carry higher loads without failing or disintegrating during the formation of the structural slab 20. However this configuration of walls and individual 15 posts also provides an ability to cope with any soil heave that may occur over tiiine as the posts and walls will collapse under pressure such that movement is rott transthitted to the slab. Whilst not shown, it will be appreciated that the shallow void forming elements 12 may also be constructed in the same manner as the spacer void forthing element 16 of Fig. 4. 20 It will be appreciated that the structure and material of the void forming elements 12, 16 ensure that they compress under load during the construction process without deforming or failing, and also ensures that they act as sacrificial members in the event of soil heave. In this regard, in the event of soil expansion in the direction of arrows A of Fig. 2, the soil is able to expand into the cavities of the void forming 25 elements 12, 16, where appropriate. As the void forming elements 12, 16 and the posts 32 are made from a foam material such as polystyrene, in the event of soil expanding into the cavities, the posts 32 can break away from the body of the void forming element 12, 16 to further accommodate the expanding soil. As discussed above, the void forming elements 12, 16 create a moisture, an 30 acoustic and a thermal barrier between the slab 20 and the ground 22, as well as protect the slab 20 from cracking and shifting due to expansion of soil. Referring to Figs. 5 and 6, a more preferred embodiment of the structure of the spacer void forming element 16 is shown in plan and elevation respectively. The void forming element 16 in this embodiment is in the form of a box-like element having four 35 vertical side members 46, 47 and a top platform member 49 forming the concrete supporting surface 48. Lower portions 46 of the side walls are corrugated and while 10 upper portions 47 of the side walls are corrugated on an inner surface and have the corrugations filled on the outer surface. The members 46, 47 49 of the void forming element 16 are configured to interface with the concrete slab 20 in the manner as shown in Fig. 2. As with the previously described embodiment, the underside 30 of the void 5 forming element 16, namely the side which is supported on the ground surface 22, is open thereby providing a cavity within the void forming element 16, The cavity is defined by the inner surfaces walls of the members 46, 49, and in the embodiment as shown in Figs. 5 and 6, again represents a substantially rectangular space, although in this instance with corrugated walls. 10 Figs 7 show an elevation of an alternative version of the spacer void forming element 16 having differing heights to that of Fig. 6. In other respects the embodiments shown in elevation in Figs. 6 and 7 are similar to one another. A plurality of strut members, in the form of posts 42, are provided within the cavity and extend from the inner surface of the platform member 49 to the ground 15 surface 22 when the void forming element 16 is positioned thereon for use. The posts 42 provide support for the platform member 49 of the void forming element 16 along its length such that the top surface 48 is able to support the load of the reinforced concrete during placement of the slab 20, as well as the load of workers or machinery used during the placement process. In this regard, the shape of the posts 42 and their 20 location within the cavity defines the strength of the void forming element. In the figure 5 embodiment the struts have a substantially rectangular cross section with two opposing concave sides. It will be appreciated that the arrangement and shape of the posts 42 can be altered ri accordance to the specific construction. Fig. 8 illustrates an embodiment of the structure of the shallow void forming 25 element 12. The shallow void forming element 12 in this embodiment is also in the form of a box-like element having four vertical side members 56 (in this case not corrugated) and a top platform member 59 forming the concrete supporting surface 58. The height of the shallow void forming element 12 is preferably the same as the height of the corrugated lower portion 46 of the walls of the spacer void forming element 16. 30 Therefore the overall height of this shallow void forming element 12 is shorter than that of the spacer void forming elements 16 to allow the formation of concrete beams between the spacer void forming elements 16. The members 56, 59 of the shallow void forming element J2 are also configured to interface with the concrete slab 20 in the manner as shown in Fig. 2. A single internal strut 52 is provided extending from the 35 inner surface of the platform member 59 to the ground surface 22 when the void forming element 12 is positioned thereon for use and the strut 52 divides the internal IlI space of the shallow void forming element into two cavities 60, each cavity is defined by the inner surfaces of walls of the members 56, 59 and the strut 52, and in the embodiment as shown in Fig. 6, again represents a substantially rectangular space. Figs. 9a and 9b show an alternative embodiment of the void forming elements 5 12, 16 of Figs. 4-7, where corresponding reference numerals indicate corresponding features with corresponding functionality. The void forming elements 12, 16 of Figs 9a and 9b include a thin-walled cellular base structure defined by a network of cell walls 70 formed by thermoforming or vacuum forming. A solid top 72 is provided over the cellular base structure to support the curing concrete slab 20. The thin-walled 10 construction of the void forming elements of Figs. 9a and 9b may assist in crumpling of the void forming elements 12, 16 due to soil heave. As showh in Fig. 9b, the void forming elements 12, 16 of Fig. 9a may be grouped together in abutting relationship to define a void form of a desired size for supporting a concrete slab during curing. Figs. 10a and 1Ob show a further embodiment of the void forming elements 12, 15 16 of Figs. 5-7. The embodiment of Figs. 10a and l0b has many features in common with the embodiment of Figs 9a and 9b, where corresponding reference numerals indicate corresponding features with corresponding functionality. As with the void forming elements of Figs. 5-7 and 9a and 9b, the void forming elements 12, 16 of Figs. 10a and l0b are formed by injection moulding. Void forming elements 12, 16 as 20 shown in Figs. 10a and 10b may be grouped together. as shown in Fig. 9b, to define a void form of a desired size fpr supporting a concrete slab during curing. In yet further embodiments (not shown), the void forming elements 12, 16 may have a lattice construction, similar to an inverted milk crate, In such embodiments, the top of the void forming elements 12, 16 may be solid, or of lattice construction with an 25 overlaying solid layer for supporting the curing concrete slab 20. Further embodiments of the void forming and suspension arrangement 10 in accordance with the present disclosure are shown in Fig. 1. - The Fig. 11 embodiments share many features in common with the earlier described embodiments, where corresponding reference numerals indicate corresponding features with corresponding 30 functionality. In one of the Fig. 11 embodiments, however, void forming elements 16 of uniform thickness/depth are used. In this embodiment, rather than using shallower void formers under the edge beams 24 of the slab 20, the ground 22 underneath the slab 20 is excavated to a greater extent under the edge beams 24, such that it is the depth of excavation rather than the thickness/depth of the void forming elements that creates the 35 space for forming the edge beams 24, In the other Fig, I I embodiment, void forming elements 12, 16 of different thicknesses are used to form the edge beams 24. Also, in 12 both of the Fig- 11 embodiments, there are no internal beams and the piles 14 terminate on underside of slab 20 instead of penetrating into slab. It will be appreciated that the system described in the embodiment above comprises a concrce slab supported on deep footings, typically screw piles, drilled 5 piles and piles designed for both tension and compression. The slab is designed to be suspended between the deep footings and the void forming elements allow concreting to be easily accomplished during construction and serves as a compressible/crushable zone during the life of the slab as the underlying soil expands- It will be appreciated that in the event of the void forming elements becoming compressed/crushed, the slab 10 remains thermally insulated. It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative 15 and not restrictive.