METHOD OF CONSTRUCTING BUILDING SLABS AND PAVEMENTS AND

STORING WATER

Technical field of the invention

This invention relates to methods of constructing building slabs and roadways and of storing water.

Background One problem fxom which on-ground concrete slabs or roadway pavements presently suffer is that they are subject to soil movement, particularly a phenomenon known as soil heave. Soil heave is due at least in part to expansion of soil particles when they become wet which results in the surface of the soil rising and applying uplifting forces to the slab or pavement resting thereon. >The uplifting forces can be high enough to lift the concrete slab or pavement in places which can cause cracking of the slab or pavement and in cases where walls are resting on the slab, cracking of those walls can also result.

In the case of roadways, cracking can result in separation of adjoining slabs at the joints and step ups and step downs in the road face. In some cases, even where continuous roadway slabs are laid, cracking can still result in step ups and step downs which can be dangerous to traffic.

Soils which have a high clay content are highly reactive to moisture levels and can cause significant damage to slabs or pavement as they expand. In order to deal with the problems of soil heave it is often necessary to remove large volumes of clay based soil from the building site or road site and replace it by suitable fill in the case of building sites and geo-fabrics and non-reactive road base material in the case ^' of roads prior to forming concrete slabs or pavement thereon. It is often also necessary to raise the level of the ground on which the slab or pavement is constructed in order to reduce the likelihood of water seepage thereunder where the water

could react with any residual clay and cause damage.

The present invention is aimed at solving or at least ameliorating the problem of soil heave on building slabs and road pavements and to that end provides a method of construction which ameliorates the aforementioned problems and which allows water to suitably be stored beneath a slab or road surface. Advantageously, the present invention provides a method of construction which allows some of the space which would have been taken up by the underlying soil especially clay based soil to be used for water storage purposes. The invention is also aimed at providing a method of construction which allows water to suitably be stored beneath building slabs, road pavements and the like, for example car parks.

Summary of the invention

With the foregoing in view, the present invention in one aspect resides broadly in a method of constructing a concrete slab or pavement, including: providing a plurality of formers having an upper wall adapted to support thereon wet concrete and support means depending from the upper wall and adapted to engage a ground surface so as to support the upper wall thereabove; providing a plurality of expansible and contractible water storage containers adapted to be housed under the upper wall of the formers, the containers having a water inlet adapted to receive run off rainwater therethrough; driving a plurality of piles through the ground surface above which the concrete slab is to be constructed or into the adjacent ground in predetermined respective locations to a predetermined founding depth; arranging the formers on the ground surface above which the concrete slab is to be constructed in predetermined locations so as to leave the plurality of piles exposed with

the plurality of expansible and contractible containers being housed under the upper wall of ^' the formers; and subsequently pouring wet concrete on the upper walls of the arranged plurality of formers and the exposed piles to form a concrete slab spaced above the ground surface and supported by the piles.

Preferably, the formers are adapted to be placed in spaced apart relationship to define voids therebetween which will fill with concrete as the building slab or pavement is being poured to form support beams integral therewith and resting on the piles.

Preferably, the method also includes setting formwork on the ground about the formers to define at least part of the perimeter of the concrete slab or pavement to be constructed prior to pouring the wet concrete. In a preferred form, the formwork is adapted to form a perimeter beam integral therewith. In the case of building slabs, it is preferred that the perimeter beam be formed with openings therein so that access to the containers may be gained therethrough if necessary for replacing the storage containers if necessary. For that purpose, it is preferred that the formers have knockout panels and that the openings formed in the perimeter beam align with such knock-out panels.

Preferably, the expansible and contractible storage containers are interconnected via the water inlets for water communication therebetween for filling and/or draining purposes so that any number of inlets can be connected to a drainage pipe or downpipe so as to fill the interconnected storage containers. Suitably, the expansible and contractible water storage containers are adapted to accommodate expansion and contraction of the underlying soil by partially collapsing.

It will be appreciated that the minimum height of the

support means, that is the height at which it supports the upper wall above the ground, will typically depend on the swell potential of the underlying soil. Preferably, such height is equal to or greater than the level to which the surface of the soil would rise if the soil were to become wet and will depend on. various characteristics of the soil, particularly, the reactivity of the soil. For example, a moderately reactive soil may have a wet to dry change in height of 30 mm while a highly reactive soil may have a change of 75 mm and an extremely reactive soil may have a change of 110 mm. Thus, while the minimum height of the support means might be 110mm in order to accommodate the swell potential of the soil it will be appreciated that a height of 300mm will provide a large space for water storage at very little extra construction cost. It will be appreciated that if the expansible and contractible storage containers are full of water and are in contact with the underside of the upper wall of the formers, any excessive soil heave will force the bottom wall of the expansible and contractible containers upwards and cause water to discharge through the downpipes thereby preventing any damage to the concrete slab by soil heave.

In yet another aspect the invention resides broadly in a method of constructing a pavement, including: providing a plurality .of concrete slab pavement sections having an upper surface adapted to support thereon vehicular traffic and a lower surface adapted to engage supporting piles, beams or foundations; providing a plurality of water storage containers adapted to be housed under the pavement sections, the containers each having one or more inlets adapted to receive rainwater therethrough; driving a plurality of piles into the ground upon which the pavement is to be constructed in predetermined respective

locations to a founding depth; placing or forming pavement section supports on said piles for supporting the pavement sections thereon; forming cavities between adjacent piles for housing the water storage containers; placing the water storage containers within the cavities; and placing the pavement sections on the pavement section supports to form a pavement above the containers. Preferably, the pavement sections include a kerb at or adjacent their side edges with stormwater outlets formed in or adjacent such kerbs, the outlets being adapted to connect to the water storage containers thereunder for fluid communication therewith. Preferably, the piles are screw piles which are provided with upper end caps selected to support thereon the pavement sections or steel or concrete beams spanning between adjacent piles for supporting the pavement sections. In a preferred form intended for the construction of residential suburban pavements (roadways) , three rows of piles are driven into the ground along the length of pavement, one row being adjacent one side edge, one adjacent the opposite side edge and one along the centreline of the pavement. In such form, beams are supported on adjacent ones of the piles in each row and the concrete slab pavement sections are then placed on the three supporting beams. Suitably, one or more bearing plates may be placed between the beams and the concrete slab pavement sections. In one such preferred form, the piles are positioned to also form lateral rows thus maximising the uninterrupted space available between piles for forming the cavities in which the water storage containers are to be housed.

It will be appreciated that some soils are naturally very loose and cavities formed by excavating such soils will often

need side wall support to prevent erosion and collapse. Thus, it is preferred that the cavities be lined or reinforced with material adapted to prevent the side walls collapsing, for example, sprayed on concrete, plastic liners, blockwork, stonework or the like.

Preferably the storage containers are expansible and contractible water storage containers which are adapted to accommodate expansion and contraction of the underlying soil by partially collapsing. Advantageously, as such containers collapse, any water that has to be expelled to allow collapse can be forced out the inlets or if specific discharge outlets are provided, out those outlets. In a preferred form, where the pavement sections include storm water outlets and those outlets are connected to the storage container inlets, it is preferred that those inlets allow flow in both directions whereby excess water can be forced out through the storm water outlets and onto the pavement where it can flow to an excess water collection point and then to a dedicated stormwater drain. Preferably, a plurality of storage containers are connected to each other for connected discharge and level equalisation to provide sufficient water for particular selected purposes for a predetermined time period. For example, water used for a selected number of households or parkland areas . Preferably, pavement sections include connection means or access means whereby stormwater drains or downpipes from adjacent properties may be directed to the storage containers via the pavement sections. In a preferred form where the pavement sections have stormwater outlets, it is preferred that such connection means or access means provide for stormwater from adjacent properties to enter the storage containers via the stormwater outlets or via a collection box under the stormwater outlets.

Preferably, the pavement section supports are height adjustable to allow the pavement sections to be easily aligned and to achieve the desired upper surface height and slope.

In another aspect the invention resides broadly in a method of storing water, including: constructing a concrete slab or pavement according to any of the methods previously described/ and connecting the inlet of at least one of the expansible and contractible containers under the slab or pavement to a rainwater or stormwater supply for example, a roof downpipe, stormwater pipe, kerbing or channelling.

In another aspect the invention resides broadly in a concrete slab or pavement constructed according to any of the methods previously described.

Brief description of the drawings

In order that the invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings wherein: Fig. 1 is a plan of the site for a dwelling house after levelling;

Fig. 2 is a cross-sectional elevation of part of- a dwelling house and the underlying ground as proposed to be constructed on the site shown in Fig. 1 according to the invention along line 2 - 2;

Fig. 3 is a cross-sectional elevation of part of another dwelling house having a concrete slab floor also constructed according to the invention;

Fig. 4 is a pictorial representation of a concrete pavement (or roadway) constructed according to the invention shown partly in cross section;

Fig. 5 is another pictorial representation of the pavement of Fig. 4 with two sections removed and shown in

line for assembly to show construction components in more detail; and

Fig. 6 is a cross sectional lateral elevation of part of the pavement of Fig. 4.

Detailed description of the drawings

The dwelling house 10 illustrated in part in Fig. 2 has a reinforced concrete slab floor 11 with an integrally formed edge beam or perimeter beam 12 extending around the perimeter, the beam having a set down 13 integrally formed therewith on which an external brick wall 14 rests adjacent an inner timber frame wall 15 which rests on the upper face 16 of the slab in known brick veneer type house construction. The slab . is constructed also with intermediate integrally formed supporting beams 18 of generally known type with reinforcing bars and mesh fabric 19 arranged throughout the slab in typical known manner. The perimeter beam rests on a plurality of spaced apart screw piles 21 around the perimeter and the intermediate beam rests on a plurality of internal screw piles 22 which are set out in a grid-like array as shown in Fig. 1.

As can be seen in Fig. 2, natural ground at the site includes a layer of unstable heavy clay soil shown as item 26 beneath which is a layer of stable soil 27, the interface between the two layers being shown by dashed line 28. Although the layer of clay soil is about 1.2m deep, only the upper 600mm is seasonally affected significantly (except in very rare occasions) by wet and dry weather during which it expands or contracts. As can also be seen in Fig. 2, a void 29 or a strip of scarified soil is provided under the perimeter beam between the piles so as to accommodate soil heave therebetween.

As can be seen in Fig. 1, the slab between the edge beam and the intermediate beams is formed on hollow pods 25 which

have been placed on the surface 31 of the clay soil 26. The pods each have an upper wall 33 and a skirt 34 which depends therefrom at its perimeter and terminates in a ground engaging foot 35 to define an open bottom 36. Suitably, the skirt supports the upper wall a distance of about 300mm above jzhe clay soil surface so as to form a void 37 thereunder in which an expansible and contractible container (or bladder) 38 is housed. Suitably, the container has an inlet 39 to which one of the downpipes from the roof of the house 10 is connected, an overflow outlet 41 which is connected to an adjacent container in the manner shown in Fig. 3, and a drain 42 which is connected to a water reticulation system.

In order to construct ' the concrete slab it will be appreciated that the soil surface 31 is prepared by levelling and if desired a layer of sand, crusher dust or the like may be placed thereon to obtain a smooth surface for supporting the pods. The pods are inverted and the expansible containers are fitted into the pods and secured therein by duct tape, adhesive or the like. The pods are then returned to their normal orientation and are then placed on the level surface in spaced apart relationship to form elongate voids therebetween whereupon reinforcing bars, fabric or the like are placed on the upper surface of the pods and supported by bar chairs or the like in known manner and similarly, suitable reinforcing bars are placed in the voids between the pods. The inlets are connected to suitable PVC pipes which pass through the edge formwork for later connection of downpipes and the overflow outlets are connected to adjacent containers by any suitable pipes, for example PVC pipes. The concrete is then poured which flows into the voids to form edge beams 12 and internal beams 18 integral with the floor with the containers being retained under the pods. Once the roof of the house has been completed, the downpipes can be connected to the containers.

The house 110 ^' illustrated in part in Fig. 3 is constructed in much the same manner as the house illustrated in Fig. 10 and corresponding numbers are used to reference corresponding items but prefaced by a ^λλ 1". The main difference is that the site profile prior to construction is as shown by line 129 and two layers of fill 126 and 131 have to be added to level the site and bring it to the required height. The first layer 131 is a relatively non-reactive layer of loam and the second layer 126 is reactive clay which has a thickness of about 900mm. It will be appreciated that the expansible and contractible container under one pod may accommodate more soil swell than under another pod and the excess water will simply move to the container which is connected to the downpipe and flow upwards into the roof . gutter or alternatively if a separate overflow is provided, the water will flow out through that overflow outlet.

The roadway 210 (sometimes referred to herein as ^' a pavement) illustrated in Figs.' 4 to 6, comprises a plurality of straight concrete pavement sections 211 and corner pavement sections 212 also constructed of reinforced concrete, which rest side by side on three generally parallel laterally spaced apart beams 213, 214 and 216 extending longitudinally along the length of the roadway with the beams 213 and 216 being adjacent the side edges of the pavement sections respectively and the beam 214 being under the centre line of the pavement sections. At the bend noted as Item 220, the beams are curved to- form concentric quadrants which correspond with the curve in the roadway. Of course, different types of curves will use different corner sections. Advantageously, the piers are also installed in lateral rows as far as possible so as to leave clear generally rectangular ground spaces between adjacent lateral rows.

Each beam is supported on a plurality of spaced apart

screw piers 215, the piers being arranged in three rows parallel to the centreline ^• of the roadway, the outer beam being supported by row of piers 217, the inner beam by row 218 and the centre beam by row 219. A bearing plate 221 lies between the upper face of each beam and the pavement section thereon to ensure that the load is evenly distributed along each beam. Advantageously, a ^' height adjustable end cap 222 is fitted to the upper end of each screw pier and the beams rest on those upper end caps. Suitably, the upper end caps can be screwed up or down to provide adjustment during construction to ensure that the pavement slab is at the desired height and if required has the desired slope.

A plurality of reinforced rubber water storage containers 226 are provided under the pavement sections in the ground spaces between the lateral rows of screw piers, the storage containers being expansible and contractible vertically.

Selected roadway sections are provided with stormwater outlets 231 which open to respective collection pits below which in turn drain into the expansible and contractible containers 226 via drainage pipes 232. If desired, each pavement section can be constructed with the collection pit having a knock out section adapted to form the storm water outlet which when knocked out opens the edge portion of the road section to the collection pit. Thus, any number of stormwater outlets can be provided in a roadway.

Footpath sections 236 ar.e provided along the side edges of the pavement sections and are secured thereto by bolts (not shown) which extend generally horizontally into the pavement section and locate in complementary recesses in the underside of the footpath section where washers and nuts can be fitted.

The roadway210 is constructed by excavating a channel 241 having a base 242 and two spaced apart generally vertical side walls 243 and 244. Shoulder excavations 246 and 247 on

opposite sides of the channel respectively are also carried out to accommodate the footpath- sections 236.

Once the channel has been formed, the piles 215 are screwed into the ground in predetermined positions through the base of the channel whereupon the expansible and contractible containers can be fitted between the rows of piers, one or more containers being locating under each pavement slab. If desired, non-expansible and non-contractible containers can be utilised although to lesser advantage in that some air space above must be left in order to accommodate soil heave which can be accommodated by the expansible containers. If necessary, the side faces ,243 ^' and 244 can be stabilised by spray-on concrete, pre-cast • -concrete slabs, rock walls,

^■ plastic sheeting, or the like to prevent the side walls collapsing.

Once the piles have been screwed into the ground, the end caps 222 are fitted whereupon the beams can be placed on the end caps and secured thereto if necessary and then, the bearing plates can be placed on the upper faces of the beams. Once the height of the beams has been set by adjusting the end caps or have been levelled as required, the pavement sections can be lifted onto the bearing plates to form the roadway. The footpath sections can be fitted to the pavement sections before placing them on the beams or afterwards if desired. Once the pavement sections are in position, the pipework connecting the containers to the stormwater pits can be fitted and the stormwater outlets created by knocking out the knockout portions. In another embodiment, the screw piles may be capped with concrete pads and the pavement sections may incorporate beams which are adapted to rest on the concrete pads.

As can be more clearly seen in Fig. 5, the drainage pipes 232 which connect the stormwater pits to the containers 226

are connected at the end walls of the containers adjacent the bottom. Advantageously, once a container fills, the connected stormwater pit also fills and water simply overflows therefrom and thence flows to the next stormwater outlet or the next one or eventually flows to a stormwater overflow at a preselected position in the roadway. Advantageously, if a container is full and the soil underlying the channel base expands upwards, water is pushed out of the container as it engages the underface of the pavement sections and collapses downwards on itself and then flows down the roadway against the kerb and into the next stormwater outlet and so on.

Water in the containers can be extracted by passing a suction hose through a stormwater pit and the inlet pipes but more suitably, the containers are provided with outlets adapted for connection to a suction pipe and pump. If desired, the tanks can be interconnected whereby water from any desired number of tanks can be extracted by a single pump at a designated pumping station. The water extracted from the tanks can then be reticulated to adjacent properties, parklands, sporting fields or the like.

The foregoing description has been given by way of illustrative example of the invention and many modifications in variations which will be apparent to persons skilled in the art may be made without departing from the spirit and scope of the invention as defined in the appended claims.