FIELD OF THE INVENTION

This invention relates to the field of providing foundations for posts or piles extending from the ground, to support signs or to support constructions such as buildings.

BACKGROUND

The usual procedure for putting up a single-storey building (at least) involves the preparation of foundations embedded in the ground, to provide a platform on which the building is to be constructed. (One alternative is a concrete slab floor). About half of the foundations used in New Zealand comprise a mass of concrete of prescribed volume, poured into a hole dug into the ground down to a prescribed depth. The mass supports a vertical member or pile generally of wood, thrust into the concrete while it is moist (when it still is wet cement). "Prescribed" refers to various building codes. Disadvantages of this process for making foundations include that a reasonable amount of wet cement has to be provided at the site, that lining up the piles requires a good deal of fiddling with temporary supporting struts, and that it can take seven days before the concrete around the piles has hardened enough for the stresses of further construction. A common trend nowadays is to use high-density particle board as the floor, to prefabricate walls of houses and nail them over the floor, and the factors encouraging this speedy building are incompatible with waiting for the foundations to harden so in many cases the unhardened foundations may have been compromised by substantial stresses while still not hard. Furthermore, there may be a need to dispose of soil removed from holes.

Foundations having engagements concealed within the soil are known. For example one current practice when building a wall is to include a dogleg at the base of the

foundations, by undercutting the soil to one or both sides at the base of a hole, so that should the wall tilt, soil has to be lifted on one side and compressed on the other. Another practice for foundations comprises belling out the base of a hole, so that when filled with concrete the base is wider than the vertical column. Again, this involves the surrounding soil in movement of the structure - whether uplift or lateral forces cause it. These practices have the disadvantages that at the time of pouring concrete, soil may move and compromise the structure, and that the curing time of the concrete can hold up a project.

OBJECT

It is an object of the present invention to provide an improved apparatus and method for construction of foundations for signs or a a structure such as a building, or one which will at least provide the public with a useful choice.

STATEMENT OF THE INVENTION

In a first aspect the invention provides a method for providing a foundation comprising the steps of excavating a hole in the ground, providing a substantially flat load-bearing surface at the bottom of the hole, and placing upon the load-bearing surface an assembly including an elongate member attached to a foundation pad wherein the foundation pad has a wider contact area than the cross section of the elongate member, so that after placement the elongate member of the assembly extends upwards from the surface of the ground in a substantially vertical direction, and the hole is filled with soil or other packable material.

Preferably the load-bearing surface comprises a sand or other base layer of particulate material. Optionally the pad may be placed directly on a flat soil base if the hole provides one.

Preferably after placing the assembly in the hole soil removed from the hole is replaced over the pad and around the elongate member and is tamped in place.

In another aspect the invention provides a foundation assembly comprising an elongate member attached to the upper surface of a wider foundation pad, the pad and a portion

of the elongate member being embedded in the ground, with a portion of the elongate member extending upwardly from the surface of the ground, the pad being situated on a base layer of particulate material.

In a further aspect the invention provides a structure comprising a plurality of foundation assemblies with at least one row of at least two such foundation assemblies, each row of foundation assemblies being connected together by a horizontal member.

Optionally, some of the assemblies may be load-bearing bases only - that is, not buried below compacted fill.

Preferably the structure has bracing means between the horizontal member and at least one of the elongate members.

Preferably each foundation assembly comprises a timber pile connected to a pre-cast concrete foundation pad by means of an elongate metal fastener.

In another aspect the invention comprises a method for providing a unit of a ground-embedded foundation for supporting a building comprising the steps of excavating a hole of at least a minimum depth in the ground, placing a base layer of particulate material at the bottom of the hole, placing upon the base layer an assembly including an elongate member attached to a base wherein the base has a larger contact area than the cross section of the elongate member, so that after placement the elongate member of the assembly extends upwards from the surface of the ground in a substantially vertical direction and then back-filling the hole with an at least partially cohesive material.

In a related aspect the invention comprises a method as described above, wherein the base layer of particulate material is sand.

In another related aspect the invention comprises a method as described above wherein the at least partially cohesive material is soil removed from the hole, tamped into place.

In yet another related aspect the invention comprises a method as described above comprising the use of at least one aligned series of units as described above, the at least

one series of units supporting horizontal support members of the base of the building upon the elongate members of the assemblies.

In a further related aspect the invention comprises a method for supporting a structure as described above, including bracing means capable of reducing inadvertent sideways movement.

Preferably the bracing means comprises at least one metal plate affixing the elongate member to one or more horizontal beams supporting the structure.

Alternatively the bracing means may comprise one or more struts affixed at an angle between the elongate member and one or more horizontal beams.

In a still further related aspect the invention comprises a method for supporting a structure as described above, comprising the use of a precast concrete slab having a central aperture as the base.

In still yet another related aspect the invention comprises a method for supporting a structure as described above, comprising the use of a wooden pile as the elongate member.

In a further related aspect the invention comprises a method for supporting a structure as described above, further comprising the use of an elongate metal rod having a widened head at one end and an insertable point at the other end as the means for attaching the base to the elongate member.

Preferably the length of the elongate metal rod is at least three times the thickness of the pad - although this may be varied somewhat to suit local conditions.

In yet another related aspect the invention comprises a method for supporting a structure as described above, further comprising the use of a resilient grommet between the widened base of the metal rod and the precast concrete slab, so that the assembly is provided with an ability to return or rebound to a normal configuration after the removal of excessive bending forces.

In a further related aspect the invention comprises a structure supported by a foundation constructed according to the method as described above.

In a third broad aspect this invention provides means for supporting a structure, comprising an elongate member protruding from the ground and held upon a base to be buried within the ground, which means is prepared prior to placement in the ground, the means including a substantially rigid base capable of being securely attached to the elongate member, wherein the base has a larger contact area than the cross section of the elongate member.

In a related aspect the invention comprises support means in which the base is made of pre-cast, cured concrete in the form of a thick slab of substantially similar length and breadth, including at least one substantially central aperture adapted for attachment to the elongate member.

Preferably the thick disk includes an insert, also known as a grommet, of a resilient material.

Alternatively the thick disk may have a polygonal bearing surface.

In another related aspect the invention comprises support means in which the bearing surface of the base, after attachment, is substantially parallel to the base of the elongate member.

In another related aspect the invention comprises support means (an assembly) in which the upper surface of the base, after attachment, is substantially parallel to the base of the elongate member, and serves during use to engage with the at least partially cohesive material filling the hole, so that a force tending to withdraw the support means must disrupt the cohesive material in the process of causing movement.

In a further related aspect the invention comprises support means in which the base is made of a plastics material, optionally strengthened with incorporated fibres or stiffening ribs.

Alternatively the foot or base may be made of a metal, a glass, protected particle board,

or plywood.

In another related aspect the invention comprises support means in which the elongate member is made of wood, oriented with its grain running substantially along the length of the member.

Alternatively the elongate member may be made of a metal, or of a plastics material, optionally strengthened with incorporated fibres or stiffening ribs.

In a further related aspect the invention comprises means for securely attaching an elongate member to a base comprising at least one attachment means capable of being forced through the base and along the grain of the elongate member.

In a related aspect the invention comprises support means in which the attachment means comprises a corrosion-resistant elongate metal shaft, having a point at a first end and a head at a second end.

In another related aspect the invention comprises support means wherein the attachment means includes friction-enhancing projections from the side of the shaft.

In yet another related aspect the invention comprises support means in which the elongate member comprises a pile, suitable for use in supporting a structure such as a building.

In a yet further related aspect the invention comprises support means in which the elongate member comprises a post, suitable for use in supporting a structure such as a sign or a fence.

In a further broad aspect the invention comprises support means in which the base, the elongate member, and the attachment means are a manufactured kit of parts capable of assembly at a building site.

In another related aspect the invention comprises support means comprising one or more unassembled components of the assembly.

In yet another broad aspect the invention comprises a method for installing the support means as when constructing a foundation for a built structure, comprising the steps of making at least one hole to accept assembled means as described in this specification, placing a bed of sand in the base of the or each hole, placing an assembled means (as previously described) in the or each hole, settling the sand while aligning the elongate members, back-filling the hole, and causing the protruding elongate members to have at least one common height so that a bearer can be secured to the protruding ends of the elongate members.

In a related aspect the invention comprises a foundation for a built structure, comprising a number of assembled support means as described in herein and as installed by means of a method as described herein.

In another related aspect the invention comprises a support for a construction, comprises a number of assembled support means as described above, attached in a manner including bracing to protect against shearing forces to at least one horizontal load-bearing beam capable of supporting a building.

Optionally, a stiffening collar may be placed about the elongate member at about the point where it emerges from the ground, thereby providing some support to the shaft of the pile.

Preferably the stiffening collar is constructed of some resilient material capable of absorbing sideways movement without giving way. Alternatively it may be poured concrete. Alternatively it may be a rigid disk (perhaps of steel) designed to cut into the ground and develop friction if sideways movement is caused.

In another aspect, the invention provides re-usable foundation means, which could be dug up and moved about as when (for example) a garden shed is moved about if the garden is remodelled.

DRAWINGS

The following is a description of a preferred form of the invention, given by way of example only, with reference to the accompanying diagrams.

Figure 1 : is a section through a foundation pad plus pile assembly according to the present invention.

Figure 2: is an illustration of pad shapes and pad-pile attachment components of the present invention.

Figure 3: is an illustration of a foundation in place, showing resistance to vertical lifting by the present invention.

Figure 4: is an illustration showing the bond between the timber pile of the present invention and a horizontal bearer, using nail plates,

Figure 5: is an illustration of a pile/bearer bond during application of an extreme lateral force.

Fi ure 6: is an illustration showing the bond between the timber pile of the present invention and a horizontal bearer, using a brace.

PREFERRED EMBODIMENT

The examples to be described herein comprise ready-to-use concrete foundation pads incorporating certain improvements, together with (generally timber)vertical support members or piles, plus attachment means. The examples may be sold as components or in a ready-assembled state (referred to here as "an assembly").

In contrast to a conventional foundation comprised of a column of concrete or wood or the like occupying a substantially vertical hole in the ground, the substantially rigid foot or base of the invention engages with a greater volume of soil below, and also above it, in the manner of a deadman used sometimes to anchor a cable in the ground. The bearing surface of the concrete pad is significantly greater than the area of the vertical pile.

An example pad has dimensions as follows: diameter 38 cm (this pad is circular), thickness 10 cm, central aperture 1.5 cm diameter, and forming the centre of a slot 5 cm in length on the base of the pad. The upper surface has a chalice-shaped enlargement 6 cm in diameter extending through about half the thickness of the pad. This widened hole is filled with a resilient "grommet" made of a degradation-resistant resilient material such as polyurethane. Currently we use a material with a Shore hardness of ^* 3A\ The grommet has a central aperture capable of admitting an about 1.2 cm diameter fixing pin which in the completed assembly passes from the base of the pad (preferably first passing through a washer) and is driven into the pith of a timber pile, to a depth of perhaps 20 cm. The pad is made of an approved grade of concrete and preferably samples from a batch are subjected to tests.

Reliance on engagement of the vertical member or pile with the surrounding soil (against side-to-side movement) is not considered by the inventors to be a desirable way to make a safe structure, because once a sideways force has been applied, the soil generally gives way and no longer holds the foundation firmly in place. By relying on the base with the soil over it as the means for maintaining the foundation in place, and not relying on the pile with the soil beside it to hold the building in place, the foundation assembly of this invention can better withstand and recover from lateral movement as might be caused by earthquakes or by strong winds, Test results given later support this view.

In other words the loadbearing (against the soil) functions are concentrated within the pad at the base, and not within that part of the pile in contact with the soil, in this invention. In contrast, a conventional poured concrete column relies rather more on contact with the sides of the column, and the weight of the poured mass.

The examples describe particular embodiments of this principle of foundation assembly construction.

EXAMPLE 1.

The base or pad (102 in Fig 1) comprises a generally hexagonal slab of concrete, cast in a former. A 100 mm thick pad satisfies the building standard NZS 3604 1990 (and in fact the assembly would satisfy that standard too). The pad has a defined usually central aperture, for attachment purposes, usually having an enlargement on one side. Preferred

dimensions are: 100 mm thick x 300 mm diameter (or more).

A hexagonal slab (or a circular one) is suitable for dropping down a hole dug by the usual means - a post-hole border and or by hand, with a shovel or the like. Square or triangular slabs tend to catch the sides of the hole and bring down dirt, and have relatively little strength. Concrete has little strength when held in tension. In this application the usual weight of the structure being supported will provide a compression bias - a sort of pre-stressing.

The concrete slab will have been made to a standard (such as thickness and also composition and method of manufacture) such that it will pass objective, prescribed tests for strength.

The aperture (Fig 2-201) through the slab may be a round hole, perhaps 10 -20 mm in diameter but more preferably it is a slot so that increased flexion can occur in one particular plane.

The aperture is enlarged usually on one side. The dimensions of the enlargement are intended to accommodate a rubber grommet or bored block of rubber 104 (intended to provide some give during lateral stresses that may be imposed on the completed foundation during subsequent seismic activity). Alternatively, urethane may be poured into a cavity cast into each base slab. With resilience provided here, the foundation can flex laterally without damage to any part. Of course the amount of resilience should be controlled so that the structure is inherently self-restoring. We usually prefer to place the resilient device on the upper side of the pad, that is, against the pile or post, although with a washer under the head of the shaft, they can be used up the other way.

The preferred attachment means comprises a mechanical fastener (Figs 1 and 2 -103) ; a very large nail or stud passed through the bored slab, through the aperture 201 in the concrete slab, and into the end of the timber pile 101 until the assembly so formed is tightly bound together. Hammering or pressing actions can be used to drive the fastener into the pile. It has been found that nailing into the end grain results in a good grip between the wood of the pile 101 and the large nail 102. Our preferred large nail 103 has a shaft diameter of about 9-12 mm, a length of 350 mm, and a head with an about (or at least) 25 mm diameter. A washer can be used under the head. There may well be

building code recommendations or minimum compliance measurements that have to be satisfied for the fastener. We prefer to cut a kind of thread 212 into the last 10 cm or so (207) of the sharp end of the nail, though optionally barbs 211 or grooves 207 may be used to assist with friction. (Surface "improvements" can be applied over the entire length). Some are shown in the enlargement of the fastener 210 at the bottom of Fig 2. The barbs may be turned back like fish-hooks to further resist separation.

Preferred nails are made of steel with suitably long-lasting anti-corrosion coatings, such as several layers of hot-dip galvanising. Alternatively nails may be made of stainless steel. These nails are not in contact with other metallic objects. Strength over time is the main requirement. A desired nail lifetime (for most applications) is at least 80 years in wet soil; the lifetime of a well-preserved timber pile.

The timber pile itself 103 may be made of tanalised pine or other suitably durable wood; acceptable to building codes for use as a foundation pile. It is generally cut from the length of the timber so that the grain of the wood is oriented lengthways. It is usually at least 125 x 125 mm in section, or is round, and in general would be supplied in a range of fixed lengths so that after emplacement the builder can trim (shorten) an array of piles to a consistent level in order to bear horizontal beams - bearers or the like. Given that there is a requirement under the building codes to bury the pad in soil so that the base of the pad is at least 300 mm deep from the soil surface, a minimum pile length of about 700 mm is determined, and so the mechanical fastener length should be somewhat less than this (to avoid opening up the entire pile centre and to minimise the risk of it being sawn through when the array of piles is levelled off)- Longer fasteners may be applicable for longer piles. In order to comply with current New Zealand building codes, these piles are typically placed 1-2 to 1.5 m apart. In fact, most measurements given herein are subject to building code requirements.

The preferred method of use is to select a pile 103 which is at least as long as the final required length, attach it by one end to a base 102, and place it in a hole of sufficient width and depth dug into the ground 301, onto a layer of 30 cm (approx minimum) of sand 303. The orientation of the pad slot and of the pile can be varied for accurate lining up. More sand is spaded in on top of the pad and around the cavity into the void at the sides of the pad. Once placed, the cavity is drenched with water so that the assembly is washed and grouted firmly into position. This resists movement that may

result when the foundation is under load or when the hole is backfilled with excavated material 302. Backfilling is preferably done with some force, such as a tamping action. It is difficult to specify the effectiveness of back-filling. Eventually, water and earthworm activity will help to "weld" the soil back into a solid form. (We have not indicated topsoil as a separate layer). After levelling the tops of a number of piles to a consistent height, bearers 305 may be attached by an approved attachment means.

Fig 3 shows a cross-section through a foundation pad and pile assembly, in place within a hole, backfilled with soil. 305 is a bearer supporting a built structure. 101 is a pile, attached (see Figs 4 and 6) to the bearer. 102 is a pad. It lies in sand 303 in the bottom of a hole, now filled with replaced soil 302. The dashed lines 304 show the approximate limits of the disturbance caused to surrounding soil in the event of the pile being pulled vertically from the hole, as might happen in the supported building was blown over by a hurricane. In other words this type of construction appears to ensure that a considerable weight of soil must be moved if the pile is pulled vertically.

Fig 4 shows a preferred means of attachment of bearers to piles. 501 is a bearer, 402 points to two joists, perpendicular to the bearer, for supporting a floor. 503/101 is a pile, and a number of nail plates 404, 505 are used to securely join the parts of the structure. The nail plates can act as braces. These nail plates, made of 0.5 to 1 mm galvanised steel, are capable of tolerating a significant sideways force without failure or without much pulling of the nails (or screws in some cases). Thus they are compatible with the use of these pads for a force-resistant foundation construction.

Using a number of these pad/pile assemblies, one can adequately support an entire house. The support is typically rated as a short cantilevered pile system.

Fig 5, traced from a photograph taken during a test, shows the effect 500 of a strong force (FORCE) applied sideways from upper right against the floor joists and so against the bearer 501 of a test structure. Note the outwards deviation of the top 500 (shown as a slight deviation from parallel) of the pile 503. On removal of the pressure this pile returned substantially to its original position, and the nail plate 505 was substantially undisturbed. During the tests, the actual forces were measured, as were the first movements (when resilience of the grommet may play some part in recovery) and further "second" movement when some lateral compression of the soil in the hole may

occur. We were pleased to observe that the structure recovered gracefully from a deflection large enough to cause the piles to be bent by (10) degrees from the vertical.

Another test (as shown in Fig 3) comprises application of an upwards force, attempting to pull the assembly up, out of the ground. A pad was pulled out of the ground by a controlled vertical force, shortly after being placed and backfilled with excavated material 302. The force required was about 800 kg and considerable ground disruption occurred to each side of the pile well beyond the perimeter of the hole itself. Heaving of the surrounding soil occurring approximately out as far as the dashed lines 304. This extensive involvement implies that the overall shape of the assembly - a narrow vertical member and a wide disc-like foot - tends to be held in well by soil. The resistance to lifting vertically appears to comprise (1) its own weight) (2) weight of adjacent soil, (3) friction) and (4) some suction. The term "adjacent" is difficult to quantify. It would depend for example on the type of soil (clay is better than sand) and the extent of back-filling and tamping down that was done, and would improve over time as the soil settles down, It is almost certainly better than a typical prior-art concrete foundation which is effectively a column of concrete without a pronounced foot - and for which the resistance to lifting vertically comprises (1) its own weight) (2) friction) and (3) suction. There will be a certain amount of adjacent soil involvement, probably not much. We recommend a hole depth of about 600 mm for general purposes, including areas with some risk of earthquakes, and 1200 mm deep holes for hurricane-prone areas.

Another bracing method is shown in Fig 6, where the construction of Fig 4 is further supported by means of an angled timber strut 601 affixed by suitable fasteners at each end. In this instance one could use "Z" nails or the like instead of nail plates.

ADVANTAGES and COMMERCIAL BENEFITS.

One principal advantage of this system over conventional poured-concrete methods is that the foundation pads can be placed, and the supporting structure can be built on top, without waiting for the usual 7 days curing time required if piles are footed in wet concrete poured into the hole. This can be a useful saving in time. If the seven day period is ignored, the concrete fails because it is stressed while only partially cured.

It appears that a structure using the invention as foundations is suitable for use in an earthquake-resistant environment; for although the foundations may be deflected by sideways motion of the earth, they are relatively resistant to permanent damage. Superstructures may still fail in themselves, but at least the foundations are not so likely to fail as are prior-art concrete foundations.

It also implies that structures built with these assemblies as foundations are relatively hurricane resistant, (in hurricanes, sideways wind forces tend to laterally shift, and roll buildings over).

The survival of other building services - such as water pipes (now usually in plastic) and electricity conduits - is assisted if the foundations have a "self-restoration" action after external wind or seismic forces.

Commercial benefits in general include :

Foundations can be made quickly and are ready for immediate use without concrete curing time delays.

Piles are held by themselves and will be substantially vertical if the hole bottom is level - no struts required.

There is no need to provide wet cement on the site, because there is no requirement for concrete infill.

Nearly all of the material removed when digging foundation holes (or a trench) is put back. Foundations are (relative to a concrete pour around a wooden pile) relatively hard to pull out of the ground.

Assemblies recover from sideways forces. (If a foundation based on a concrete pour around a wooden pile is forced sideways, the soil will become more compacted under compression and will not recover to the same extent.)

The foundations could be re-used, if for example they had been used to support a garden shed, and the shed was later to be moved to some other position. They can be dug up and handled individually; whereas a poured concrete foundation is generally too heavy and unwieldy to handle.

In its simplest form a preferred foundation assembly has a timber pile attached to the

upper surface of a wider pre-formed concrete pad by means of an axial transfixing shaft running from the lower surface of the slab. The pad has a recess facing the bottom of the pile, with a resilient grommet situated in the recess in contact with the base of the pile. The pad with pile attached is placed on a sand layer at the bottom of a dug hole and the hole is then filled with soil and tamped down to hold the foundation assembly in place. The resulting assembly has good resistance to deflection, loadbearing, and vertical uplift forces so becoming suitable for hurricane and earthquake-prone areas. Single assemblies are suitable as a foundation for signposts and fence posts.

FURTHER VARIATIONS

Assemblies tested to date are generally suitable for buildings as big as a house or a farm shed, or as small as a garden shed. Garden sheds, being not intended for habitation, are outside the New Zealand building codes. We expect to be able to scale up the dimensions (or the number) of the various parts of the assemblies in order to provide satisfactory foundations for larger buildings such as two-storey buildings.

Scaling down the structure, smaller pads can be used for decking, such as a deck joined to a house, or for sign posts and fenceposts. In this case, the item termed a "pile" is now a post of a desired height.

Other materials may be used. Generally any material has to satisfy immediate load-bearing criteria, and also has to maintain those criteria over a long period, such as 80 years.

A plastic foundation pad may be used. The material may be recycled terephthalates ("Mylar") as used in carbonated beverage containers, or polythenes from discarded milk bottles, or some other source of plastics material, which may be virgin rather than recycled. Fibre reinforcing, as with glass fibre, may be used, further stiffness may be provided by the use of strengthening ribs within a moderately thick pad. Alternatively, resilience may be provided as an innate property of this type of pad.

If pad weight is important, particularly during the early stages of settling, concrete including ironsand may be used, or the pad may be made of a metal slab; perhaps cast iron. Signposts or fence posts could be supported on a metal sheet.

Piles could be made from metal pipe, particularly in areas where wood is in short supply. If resilience is provided at the pile ase junction, pile fracture is unlikely. A fixing means may comprise a bar across or near the base of the metal pile. Preferably the inside is filled with some space-occupying material in order to exclude water.

A stiffening collar may be placed about the pile at about the point where it emerges from the ground, thereby providing some support to the shaft of the pile. The stiffening collar may be constructed of some resilient material capable of absorbing sideways movement without giving way. Alternatively it may be poured concrete, simply poured into an incompletely backfilled hole. Alternatively it may be a rigid disk (perhaps of steel) designed to cut into the ground and develop friction if sideways movement is caused. Possibly even a lead/rubber composition may be used here for damping seismic movements.

Finally, it will be appreciated that various alterations and modifications may be made to the foregoing without departing from the scope of this invention as claimed.