Improved Screw Pile TECHNICAL FIELD

[0001] The present invention relates to piles, such as screw piles or blade piles, for use in systems and methods for the construction of buildings. In some embodiments, the piles are for use in friable or loosely compacted soils. In other embodiments, the piles are for use in sesmically active zones.

BACKGROUND ART

[0002] Recent seismic events such as the Christchurch and Tohoku earthquakes in New Zealand have again demonstrated the devastation such events can cause. In each of these events and many other significant seismic events, one of the biggest dangers posed is the threat of building collapse. This is due primarily to damage that building infrastructure sustains during such events.

[0003] At present there are a number of different approaches to counter the effects of earthquakes on building infrastructure. In most cases the design solutions focus on base isolation, mass dampening or elevation control. In the case of base isolation systems, different types of bearings such as a lead rubber bearing, roller bearing, springs with damper base isolator etc, are used to isolate the buildings foundations from the earth. Mass dampening usually employs tuned mass dampeners (e.g. large weights made of concrete or steel etc) which are moved in opposition to the resonance frequency oscillations of the structure in response to the seismic wave. Elevation control is a technique unique to pyramidal constructions. The elevation configuration of such structures permits resonant amplifications within the structure to disperse the shear wave energy.

[0004] An alternate form of dampening is hysteretic damping. There are four major groups of hysteretic dampers, namely, fluid viscous dampers (FVDs), metallic yielding dampers (MYDs), viscoelastic dampers (VEDs) and friction dampers (FDs). Each group of dampers has specific characteristics, advantages and disadvantages for structural applications. In each case hysteretic dampers are designed to have a more reliable seismic performance than that of a conventional structure at the expense of the seismic input energy dissipation. [0005] In any event most conventional earthquake dampening systems are designed to primarily combat the lateral (shear) load on a building (often referred to as the sideways kick) with little to no thought to absorption or dissipation of longitudinal (i.e. uplift) forces imparted by the wave. Another factor that most dampening systems do not take into consideration is the potential for soil liquefaction. Soil liquefaction typically occurs when saturated soil substantially loses strength and stiffness in response to the stress imposed by the seismic waves transforming the soil from a solid to a liquid. Liquefaction is a significant consideration for reactive soil types. In the case of the Christchurch earthquake soil liquefaction was the cause of many collapses with many building simply sinking into the soil leading to their eventual collapse.

[0006] Geary it would be advantageous to provide a system and method of construction which reduces the impact of torsional, shear and vertical forces often associated with seismic events. It would also be advantageous to provide a system and method of construction that reduces the risk of structural collapse due to soil liquefaction or the like associated with seismic events.

[0007] Other difficulties may be encountered in using screw piles in friable soils or aerated soils. Use of screw piles in such soils may cause difficulty because the soil may not have sufficient "strength" to properly support the screw pile. In such instances, when sufficient load is applied to the screw pile, the soil surrounding the screw pile may effectively collapse within itself, thereby allowing movement of the screw pile. This effect has been noticed in some soils in southern India in which the soil structure includes a coarse material that binds with sand and clays, creating a very unusual aerated mass that provides high levels of natural drainage and therefore a constant high level dry and aerated condition. This soil has been noted as being self- supporting, but under a specific isolated point load it will shear and collapse. Similar difficulties had been found with using screw piles in areas that have very low load-bearing soils, such as saturated clays/silts in estaurine areas that also contain high levels of decayed matter.

[0008] It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.

SUMMARY OF INVENTION

[0009] The present invention is directed to a screw pile which may at least partially overcome at least one of the abovementioned disadvantages or provide the consumer with a useful or commercial choice.

[0010] Accordingly, in one aspect of the present invention there is provided a screw pile for insertion into the ground to an installation depth, said screw pile including: a shaft; a first set of blades disposed on the shaft at or towards a lower end of the shaft and a second set of blades disposed on the shaft, the first set of blades and the second set of blades being spaced apart from each other.

[0011] In some embodiments, each set of blades comprises a pair of blades for engagement with the ground.

[0012] In use of the screw pile in accordance with the present invention, a body of soil is captured between the first set of blades and the second set of blades. This assists in more securely locating the screw pile in the ground. Without wishing to be bound by theory, the present inventors believe that the soil that is captured between the blades can act as a friction body that presents a relatively large surface area to surrounding soil. This increases the effective area of contact between the screw pile and the surrounding soil and provides an increased soil mobilisation pattern.

[0013] The blades may be in the form of a flat plates extending outwardly from the shaft. Each set of blades may comprise two plates. The plates of each set may have opposite pitch to each other. In some embodiments, the lowermost part of each plate of the lower set of plates is positioned above a lowermost part of the shaft so that the shaft extends below the plates and can contact the ground prior to the plates. In this fashion, the shaft extends below the blades of the lower set of blades and the lower end of the shaft contacts the ground before the blades contact the ground. Suitably, the lower end of the shaft may be fitted with or formed with an attack bit. The attack bit engages with the ground when the screw pile is being screwed into the ground and this acts to stabilise the screw pile as it is being screwed into the ground. The attack bit may take the form of two diametrically opposed points formed on the lower end of the shaft.

[0014] In some embodiments, the leading edge of the blades may include a portion that extends at an angle to a perpendicular line extending from the shaft (when viewed from above).

[0015] The leading edge of the blades may comprise two or more discrete portions extending at different angles to each other. For example, the leading edge may have an innermost portion that is adjacent to the shaft that extends in a direction that is generally perpendicular to the shaft. A second portion may extend from the first portion, with the second portion extending at an angle to the first portion. The second portion is desirably a swept back portion. The leading edge may also comprise further portions. For example, the leading edge may comprise a third portion extending at an angle to the second portion and, in some embodiments, even a fourth portion extending an angle to the third portion. Desirably, the third portion sweeps back from the second portion and the fourth portion sweeps back from the third portion. In this embodiment, the portions of the leading edge may be generally straight edge portions.

[0016] In other embodiments, the leading edge may smoothly sweep back from the innermost portion thereof located adjacent to the shaft. In this embodiment, the leading edge may take the form of a curved leading edge that progressively sweeps back as it extends away from the shaft.

[0017] The leading edge of the blades of the screw pile in accordance with the present invention has at least one portion that sweeps back from the direction of rotation of the blade during insertion of the screw pile into the ground. The at least one portion that sweeps back from the direction of rotation of the blade assists in deflecting any rocks that may be encountered during insertion of the screw pile into the ground. In this way, impact loads on the leading edge of the blade during insertion of the blade into the ground are lowered.

[0018] In some embodiments, the rear part of the blades may comprise a generally square or rectangular part.

[0019] In some embodiments, the trailing edge of the blades may include a portion that extends at an angle to a perpendicular line extending from the shaft (when viewed from above). The trailing edge may include a first portion and a second portion extending at an angle to the first portion. Alternatively the trailing edge may smoothly sweep back towards the shaft. In these embodiments, the trailing edge also sweeps back towards the shaft. This also assists in deflecting rocks or other hard material away from the trailing edge of the blades during insertion of the screw pile into the ground. Further, the swept back trailing edge forms a "widened opening" between the blades, thereby reducing the tendency for rocks or other hard material to become jammed between the blades.

[0020] In some embodiments, the tailing edge may mirror the shape of the leading edge. [0021] The screw pile in accordance with the present invention, in having two blades in each set of blades, also provides for greater stability during the insertion phase of the screw pile into the ground. In this regard, each blade engages with the ground as the screw pile is being screwed in. Therefore, the forces applied to each blade in each set by engagement with the ground tend to cancel out with each other to thereby result in a more even distribution of forces on the screw pile during insertion.

[0022] The use of two blades in each set of blades in the screw pile of the present invention provides a further benefit. It will be understood that as the screw pile is screwed into the ground, the earth is disturbed as the blades of the screw pile are rotated through the earth. Once the screw pile has reached its installed depth, there is a section of earth located near the leading edges of the blades that has been undisturbed because the blades have not passed through that section of earth. Those skilled in the art will readily understand that undisturbed earth typically demonstrates a greater capacity for bearing load than disturbed earth. As there is a region of undisturbed earth near the leading edge of two blades in the screw pile of the present invention, the load bearing capacity of the installed screw pile in accordance with the present invention should be enhanced when compared with the load bearing capacity of conventional screw piles having a single helical blade.

[0023] A further advantage arises in that earth is positioned above both blades in each set of blades of the screw pile of the present invention when the screw pile is installed in the ground. Thus, resistance to lifting forces applied to the installed screw pile should be enhanced when compared to conventional screw piles having a single helical blade.

[0024] The behaviour of the screw pile under both compression and tension may be further enhanced in embodiments where the rear part of the blades comprises a generally square or rectangular part.

[0025] In embodiments where the blades are made from generally flat plates, fabrication of the screw pile may be greatly simplified. For example, elliptical cutouts or recesses may be formed in the blade, with the shape of the elliptical cutout or recess following the shape of the outer periphery of the shaft along the angle at which the blade is to be mounted to the shaft. The blade may then be simply cut or stamped and subsequently welded to the shaft. This is a simpler fabrication route than with conventional single helical bladed screw piles, which typically involve forming a semi-circular plate and shaping that plate into a helical flight for subsequent attachment to the shaft. [0026] In embodiments where the blades are in the form of generally flat plates, the leading edge may be formed to the desired shape by stamping or cutting the leading edge.

[0027] The shape and/or size of the blades may vary in accordance with the proposed use of the screw pile. For example, for screw piles intended to be used in sandy soils or easily friable soils, a wide blade may be used. A wide blade is appropriate because the screw pile can be easily screwed into the sandy or friable soil. Further, the wide blade assist in spreading compression and tension loads applied to the screw pile into the soil around the screw pile. For screw piles intended to be used in clay sites, a less wide blade may be used. For screw piles intended to be used in sites having rocky ground, even less wide blades may be used to facilitate penetration of the blade through the earth during installation. The blades used on the screw piles may have further swept back portions to enhance the deflection of rocks during installation.

[0028] In some embodiments, the blades used in the upper set of blades may be larger than the blades used, in the lower set of blades. In this embodiment, a generally frusto-conical body of soil becomes trapped between the upper set of blades and the lower set of blades.

[0029] The thickness of the blade may also be increased if the screw pile is to be used in sites that require greater force for installation.

[0030] In some embodiments, the leading edge of the blade may be bevelled or sharpened in order to enhance penetration of the leading edge through the earth as the screw pile is screwed into the ground and to enhance the ability of the blade to deflect rocks or other hard material.

[0031] The shaft may comprise a unitary shaft. In other embodiments, the shaft may comprise two or more shaft pieces or shaft segments joined together. The two or more shaft pieces or shaft segments may be joined together using bolts or brackets. Alternatively, adjacent shaft pieces or shaft segments may be joined together by providing a male connector in one of the shaft pieces or shaft segments and a complementaryfemale connector in the adjacent shaft peace or shaft segment. For shaft pieces or shaft segments that will form an intermediate part of the shaft (for example, if three or more shaft pieces or shaft segments are joined together to form a shaft, there will be a top piece or segment, a bottom piece of segment and one or more intermediate pieces or segments), the intermediate shaft pieces or shaft segments may have a male connector at one end and a female connector at another end. The male connector may be welded to the shaft. The female connector may be welded to the shaft.

[0032] In one embodiment, the male connector or the female connector, or both, may be provided with a face that includes serrations or radially extending grooves or depressions that enable the faces of the male connector and the female connector to lock together when they are connected.

[0033] The male connector may comprise a plug for insertion into an end of the shaft piace or shaft segment. One or more steps or shoulders may be provided to act as a welding collar, to improve the quality of weld when the male connector is connected to the shaft. The male connector may include a screw threaded projection. The female connector may comprise a plug for insertion into an end of the shaft piece or shaft segment. One or more steps or shoulders may be provided to act as a welding collar, to improve the quality of weld when the female connector is connected to the shaft. The female connector may be provided with a threaded bore into which the screw threaded projection of the male connector may be screwed.

[0034] In some embodiments, the male connector or the female connector, or both, may be provided with driving lugs to enable the screw pile to be driven into the ground.

[0035] By providing the shaft in the form of a plurality of shaft pieces or shaft segments joined to form the shaft, it is possible to easily provide shafts of varying length. It is also possible to provide shafts of varying stiffness. For example, if a rigid shaft is required, a number of relatively short shaft pieces or shaft segments may be joined together. It will be understood that the connectors may function to enhance the stiffness of the shaft and by providing relatively short shaft pieces or shaft segments, the number of connectors is increased. Alternatively, if it is desired to provide a more flexible shaft, a smaller number of longer shaft segments may be used.

[0036] In some embodiments, the screw pile further comprises a stabiliser mounted about the shaft adjacent or near an upper end of the shaft, wherein the stabiliser is positioned a predetermined distance below ground level on insertion of the screw pile to the installation depth.

[0037] The position of the stabiliser within the ground may depend on a number of factors including soil type, typical moisture content of the soil, etc. Accordingly, the stabiliser is positioned on the pile such that on insertion of the pile to the installation depth the stabiliser is positioned at an appropriate depth for the given building site. In some case the stabiliser may be positioned at a depth between lm to 2m below ground level or deeper if required. In some case the stabiliser may be positioned at or adjacent ground level.

[0038] In some embodiments, the stabiliser includes one or more fins which extend outwardly relative to the shaft. The fins may be arranged radially about a sleeve which is fitted over the shaft. The sleeve may be able to rotate relative to the shaft. The sleeve may be positioned between a pair of collars attached to the shaft. Suitably there is a degree of clearance provided between the sleeve and the collar to allow the sleeve and fins a degree of longitudinal movement with respect to the shaft. A dampening material may be provided between the exterior surface of the shaft and the interior surface of the sleeve. Preferably the sleeve is a cylindrical construction. The sleeve, fins and collars of the stabiliser may be constructed from a steel of a suitable grade and strength e.g. mid steel, high tensile steel or other hardeened metals.

(0039) If the screw pile of the present invention is to be used in seismically active areas, the first set of blades and the second set of blades are suitably positioned below the liquefaction zone. In this manner, the first set of blades and the second set of blades remain in soil that does not liquefy during an earthquake, thereby securely holding the lower part of the screw pile in position. The stabiliser, which is typically located on an upper part of the shaft of the screw pile, will normally be positioned in the liquefaction zone. During periods of soil liquefaction, the stabiliser is released from binding contact with the soil, to allow the full length of the shaft to absorb energy between the two sets of blades at the lower end of the shaft and the building located on top of the screw pile. The two spaced sets of blades are end load bearing and work for both tension and compression loads. The two spaced sets of blades lock up the base section of the pile by mobilising the soil between the dual blade sets. This creates a "friction mass" to resist rotation of the pile base when lateral spring loads are applied to the upper length of the screw pile during an earthquake. Therefore, the screw pile can continue to remain securely in place during an earthquake event.

[0040] The screw pile may also include a connector positioned on the upper end thereof to enable the screw part to be connected to a building element. The connector effectively provides a connecting interface between the screw pile and the building. The connector may be as simple as a plate to which a building element, such as a truss or a joist or a frame member, may be joined, for example, by bolting or screwing.

[0041] In some embodiments, the connector may take a more complex form. In one embodiment, for example, the connector may provide a first plate secured to an upper end of the shaft, a spring having a lower end connected to the first plate and an upper end connected to a second plate. The spring acts to space the first plate from the second plate. In this embodiment, the building element is connected to the upper plate. Advantageously, the spring can allow for movement between the building and the screw pile during an earthquake which can greatly alleviate any damage that may otherwise be caused to the building during an earthquake.

[0042] In other embodiments, the connector may comprise a head assembly for engagement with the upper end of the shaft such that a slip joint is provided between the head assembly and shaft.

[0043] The head assembly may include a sleeve and support section. The sleeve may be designed to fit over the upper end of the shaft. The sleeve may be attached to the top of the plie via a spring which has one end attached to the top of the pile while the opposing end is attached ) to the sleeve. Suitably the sleeve is coupled the support section via a neck. The neck may be a cylindrical steel construction sized to fit inside the internal diameter of the sleeve and over the external diameter than that of the pile.

[0044] Preferably the sleeve is designed to fit over the end of the pile such that a slip joint is created between the two components with the spring being positioned to prevent total release of the sleeve from the pile.

[0045] A dampening ring may be positioned in the overlapping region between the exterior surface of the shaft and the interior surface of the sleeve. The dampening ring may be constructed from rubber, ruber compound, a suitable polymer or other suitable compound material.

[0046] Suitably the support section is fitted to the upper end of the neck via a threaded rod. The rod may be attached to a support plate, which ties the pile to the building. The rod may be coupled to a cap positioned over the end of the neck. The rod may be secured to the neck via engagement with a nut disposed within the end of the neck. The nut may be mounted within the neck such that a pivot joint is formed between the neck and the rod. A dampener may be positioned between the cap and neck. The dampener may be constructed from rubber, ruber compound, a suitable polymer or other suitable compound material.

[0047] In a second aspect of the present invention there is provided a building system including: a plurality of screw piles as described herein; and a building element joined to and located above the screw piles.

[0048] In a further aspect of the present invention there is provided a method of constructing a structure with improved seismic response the method including the steps of: installing a plurality of screw piles as described herein within the ground at a site, wherein the first and second blade sets of each pile is positioned a depth greater than the site's determined liquefaction depth; and

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connecting a building element to the screw piles and completing erection of a building above the screw piles.

[0049] Suitably the shaft is of sufficient length that when the pile is sunk to the installation depth the first and second blade sets are positioned beyond the liquefaction depth for the soil at the chosen construction site. The liquefaction depth may vary as it is dependant upon the ground conditions and earthquake intensity expected at a given site be determined. The liquefaction depth for a chosen sit can be determined by standard methods.

BRIEF DESCRIPTION OF DRAWINGS

[0050] In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings, which illustrate preferred embodiments of the invention, and wherein:

[0051] FIG. 1 is a schematic view of a screw pile for use in the construction of a slab according to one embodiment of the present invention;

[0052] FIG. 2 is a schematic diagram depicting the construction of a blade for use with the screw pile of Fig 1 ;

[0053] FIG. 3 is a schematic depicting the screw pile of Fig 1 in situ ;

[0054] FIG. 4 is a detailed view of a stabilising mechanism for use with a screw pile according to one embodiment of the present invention;

[0055] FIG. 5 is a detailed view of a section of a head assembly for use with a screw pile according to one embodiment of the present invention;

[0056] FIG. 6 is a is a detailed view a further section of a head assembly for use with a screw pile according to one embodiment of the present invention;

[0057] FlGs 7A to 7D depict alternate arrangements of a head assembly of a with a screw pile according to one embodiment of the present invention;

[0058] FIG. 8 shows a front view of a screw pile in accordance with another embodiment of the present invention;

[0059J FIG.9 shows a view, partly in cross-section, of a concrete slab being formed on the top part of screw pile showing in FIG. 8;

[0060] FIG. 10 shows a front view of a floor joist or support beam being attached to the top of a screw pile as shown in FIG. 8;

[0061] FIG. 11 shows an exploded view of connecting elements used to connect to shaft segments together;

[0062] FIG. 12 shows a top view of the female connector shown in FIG. 11

[0063] FIG. 13 shows a front view of a screw pile in accordance with another embodiment of the present invention;

[0064] FIG. 14 shows a perspective view of the screw pile shown in figure 13; and

[0065] FIG 15 shows a schematic view of the screw pile shown in FIGs 13 and 14 installed in the ground.

DESCRIPTION OF EMBODIMENTS

[0066] It will be appreciated that the drawings have been provided for the purposes of describing preferred embodiments of the present invention. Therefore, the person skilled in the art will understand that the present invention should not be considered to be limited solely to the features as shown in the drawings.

[0067] With reference to Fig 1 there is illustrated one possible arrangement of a screw pile 100 for use in the construction of a building. In the present example the screw pile 100 is generally of the type discussed in the applicant's earlier filed international application

PCT/AU2008/001668 which is herein incorporated by reference, and includes a shaft 101 with upper 1011 and lower 101 ₂ ends. Shaft 101 is a generally cylindrical and is typically constructed — fronrsteel of a suitable grade an strength e.g. mild steel7fiigh^nsile ^~ steel etc.

[0068] Like the pile of the applicant' s earlier application the lower end 101 ₂ of the shaft is adapted to be driven within the ground to a predetermined depth. The lower end 101 ₂ in this case may include an attack bit 103. However unlike the pile discussed in the applicant's earlier application the lower end 101 ₂ of the pile in this instance includes two sets 104j, 104 ₂ of blades 1051 , 105 ₂ mounted to the outer periphery of the shaft 101. As shown the blade sets 1041 , 104 ₂ are disposed at a predetermined distance d from one another e.g. lm. In addition to the inclusion of a secondary 104 ₂ set of blades 105|,105 ₂ the screw pile of the present invention also includes a number of adaptations to improve the piles overall seismic performance which are discussed in greater detail below.

[0069] During installation of the screw pile 100 the attack bit 103 is utilised to make the initial penetration. As the attack bit 103 bites into the ground it assists in maintaining the screw pile in the desired position during installation. Once the attack bit 103 has penetrated a short distance the into the ground, the first set of blades 104i of the pile 100 then engage and dig into the ground. This causes rotation of the pile 100 thereby driving the pile into the ground with a screwing motion. As rotation of the pile 100 continues the second set of blades 104 ₂ engage the ground behind the first set of blades 104i. The use of the secondary blade set 104 ₂ in this instances acts to lock the soil behind the first set of blades 104j and provides additional lateral stability for the pile.

[0070] The upper end 1011 of the shaft 101 in this instance includes driving lugs 106 disposed on opposing sides of the shaft 101. The driving lugs 106 engage with a driving mechanism to facilitate insertion of the pile 100 into the ground. In addition the upper ehd of the shaft 1011 is adapted to receive a head assembly 107 (not shown) which is discussed in greater detail below.

[0071] Fig 2 depicts one arrangement of the blades 105i, 105 ₂ with respect to the shaft 101. For purposes of clarity only a single blade 105 is shown. It will of course be appreciated by those of skill in the art that the remaining blades are of a similar construction and are arranged in a similar manner. As shown, blade 105 has a leading edge, generally indicated by reference numeral 200. The direction of rotation of the blade 105 is shown by the arrow 201. In this case the rotation is in an anticlockwise direction. In the depicted example the blade 105 is of a generally square or rectangular construction, however it will of course be appreciated by those of skill in the art that the blade may be any suitable construction that facilitates breaking and/or cutting of the earth as the pile 100 is inserted to the desired depth.

[0072] The leading edge 200 acts to cut the earth as the blade 105 is rotated during insertion of the pile 100, that is the leading edge 200 engages with and breaks the earth as the screw pile is screwed into the ground. The leading edge 200 includes a first portion 202, a second portion 203 and a third portion 204. First portion 202 is located adjacent to the shaft 101 and extends generally perpendicular to the outer peripher of the shaft 101. In this regard, first portion 202 of the leading edge of blade 105 may be considered to extend in the radial direction from the shaft 101.

[0073] The second portion 203 of the leading edge 200 sweeps back from the first portion 201. Similarly, the third portion 204 sweeps back from second portion 203. In this way, if the second portion 203 and/or the third portion contact rocks or other detritus of hard material during insertion of the pile 100, the sweep angle of these portions assist in removing or deflecting the rocks or hard material, thereby facilitating insertion of the pile 100 and minimising the likelihood of damage to the screw pile or to the equipment used to sink the pile 100.

[0074] The first portion 202 of the leading edge 200 may be considered to comprise a small and strong initial straight blade attack region. The second portion 203 may be considered to comprise a medium follow-on, swept blade attack region. The third portion 204 may be considered to comprise the largest follow-on, increased sweep blade attack region.

[0075] In addition to the leading edge of the blade having the first, second and third blade attack regions the trailing blade is also provided with blade attack (not shown) regions of equal and opposite portions to the first, second and third blade attack regions on the leading edge. The provision of the blade attack regions of equal and opposite sweep acts to equalise the pressure on the blade. The equalisation of pressure on the blade further stabilises the pile during insertion and reduces the risk of damage to the pile.

[0076] For example if the attack regions of the trailing edge are larger than that of the leading edge the pressure at the leading edge is lower than that on the trailing edge. This pressure differential can prevent the blades from properly clearing soil and other debris as the pile is driven to depth. This can result in damage to the blades, pile shaft and even the drive equipment. In addition the pressure differential may also cause lifting of the pile which can lead damage of the drive equipment.

[0077] Moreover, even distribution of pressure on the blade reduces the risk of the pile lifting during insertion and damage to the pile due to cavitation. In this case cavitation can be caused by pockets of lower pressure in the soil above the blades. As the soil is fractured by the leading edge the looser, less dense soil passes over the trailing edge of the blade causing a difference in pressures at the edges of the blade. This can result in the pile needing to be driven harder to effect insertion which can lead to over torqueing of the pile resulting in damage the shaft and/or drive equipment.

[0078] Fig 3 depicts the pile 100 of the present invention in situ with the majority of the shaft 101 retained within the ground. As shown, the lower end 101 ₂ of the shaft 101 has been sunk to a predetermined depth. More specifcally the lower end 101 ₂ of the shaft 101 is positioned at a depth such that the blade sets 104 _l5 104 ₂ are positioned below the depth of liquefaction 301. In the depicted example the liquefaction depth is assumed to be approximately 12m. It will of course be appreciated by those of skill in the art however that the depth of liquefaction is a representative depth and denotes the depth the soil is likely to liquefy and as such is a function of the ground conditions and earthquake intensity expected at a given site and as such will vary depending on the soil composition of the site.

[0079] As can be seen in this example the shaft is also fitted with a stabiliser 108. The stabiliser 108 is located on the shaft 101 such that on insertion of the pile 100 to the desired depth the stabiliser is positioned a predetermined distance beneath ground level 302. During seismic event and soil liquefaction the stabiliser 108 assists the pile remaining in the proper orientation. Once the soil begins to regain stiffness the stabiliser acts to tie the upper section of the pile 100 back into the soil. A more detailed discussion of the construction of the stabiliser is provided below.

[0080] As can be seen in the example depicted in Fig 3 the upper section 1011 of the shaft 101 extends above ground level 301. As noted above the upper end 1011 of the shaft 101 is adapted for receipt of head assembly 107 which couples the pile to the building. In this case, as in the case of the applicant's earlier filed international applications PCT/AU2008/000147 and PCT/AU2010/000233 which are herein incorporated by reference, the building is supported on a concrete slab constructed on and formed above a plurality of screw piles 100. Further details on the construction of the head assembly are provided below.

[0081] Fig 4 is a cross-sectional view of the stabiliser 108, with the stabiliser in this case being shown in situ on shaft 101. As shown, the stabiliser includes fins 109i, 109 ₂ disposed on opposing sides of sleeve 110 positioned over the shaft 101. While only a pair of fins are shown in this example it will of course be appreciated by those of skill in that art that any number of fins may be utilised. The fins may desirably be equi-spaced around the sleeve. The sleeve 110 in this case is disposed between two collars 112 attached to the shaft 101. The clearance between the collars 112 and the shaft 101 allows the stabiliser 108 to accommodate any uplift during a seismic event without applying additional loading to the plie (i.e. stabiliser is free to slide between the collars during minor tremors etc which may not necessarily effect the remainder of the pile).

[0082] To reduce the impact of lateral forces acting on the pile 100 a dampener 111 is provided between the exterior surface of the shaft 101 and the interior surface of the sleeve 110. The dampener 11 1 may be constructed from rubber, ruber compound, a suitable polymer or other suitable compound material. During minor seismic events the damper is able to absorb the lateral shock from the seismic wave. The dampener 11 1 also assists in maintaining the stabiliser 108 in proper vertical alignment about shaft 101.

[0083] As can be seen from Fig 3 the head assembly 107 includes two main components, the sleeve 113 and support section 114. Fig 6 depicts the construction of the sleeve 113 of the head assembly 107 in further detail. In this particular example the sleeve 113 is designed to fit over the upper end 1011 of the shaft 101. The sleeve may be attached to the top of the plie via a spring 115 which secured to the pile via a bolt 118 while the opposing end is attached to the sleeve 113 via a bolt 118 inserted through the top of the sleeve 113. As can be seen the bolt in this case not only attaches the spring 115 to the sleeve 113 but also couples the sleeve to the support section 114 via support member 116 in the form of a neck portion. The neck 116 in this instance like the pile is a cylindrical steel construction sized to fit inside the internal diameter of the sleeve 113 and over the external diameter than that of the pile 100.

[0084] As the sleeve 113 is designed to fit over the end of the pile 100 a slip joint is created between the two components with the spring being positioned to prevent total release of the sleeve 1 13 from the pile 100. In addition to preventing the sleeve from lifting off the pile the spring 115 acts to absorb the longitudinal shock (i.e. lifting and down forces) imparted on the pile by the supported structure during a seismic event. In the event that the plie is forced up or the building down the spring is compressed either against the upper end of the sleeve or the pile, causing the sleeve 113 and pile 100 to slide relative to one another. After the shock has subsided the spring is released from compression forcing the sleeve 113 into its initial position with respect to the pile.

[0085] To ensure that the proper alignment of the sleeve 113 over the end of the pile 100 dampening ring 117 is positioned in the overlapping region between the exterior surface of the shaft 101 and the interior surface of the sleeve 113. The dampening ring 117 is able to absorb lateral shocks imparted on the join without affecting its overall function. Dampening ring 117 may be constructed from rubber, ruber compound, a suitable polymer or other suitable compound material.

[0086] The construction of the support section 114 is shown on Fig 5. The support section 114 is fitted to the upper end of the neck 116 via a threaded rod 119 which is attached to support plate 120. Support plate 120 in this case ties the pile 100 to the building slab. As shown the rod 119 passes through nut 121 disposed in cap 122 which is positioned over the end of the neck 116. The end of the rod 119 is then engaged with nut 123 disposed within the end of the neck 116. The nut 123 is mounted within the neck such that a pivot joint is formed between the neck 116 nut 123 and the rod 1 19. The pivot joint allows the support assembly to take torsional forces imparted on the support 114 during a seismic event. A dampener 124 may be positioned between the cap 122 and neck 1 16. Again the dampener 122 is provided to absorb torsional forces resulting from a seismic event.

[0087] As noted above the plate 120 is supported by threaded rod 119, this enables the distance between the plate 120 and the cap 122 to be varied by screwing the threaded rod into or out of nuts 121, 123. This threaded adjustment allows the plate 120 to be shimmed to level the slab if required .

[0088] Fig 7 A depicts another possible arrangement of the head assembly 700 of the present invention. As shown the head assembly 700 in this case includes a cap 701 positioned on a threaded rod 703 which is coupled to the upper end of the shaft 1011. In this case the cap 701 is positioned between two nuts 7041, 704 ₂ with spring 702 positioned between nut 704 ₂ and the upper end of the cap 701. The rod 703 and nut 7041 in this case are attached to a support beam 707 (e.g. timber joist/bearer, steel beam such as an I beam or the like or other such foundation structures). As in the above examples the spring 702 acts to absorb the longitudinal shock (i.e. lifting and down forces) imparted on the pile by the supported structure during a seismic event. In addition the spring 702 is of sufficient stiffness to absorb lateral shock reducing the need for the use of dampener between the cap 701 and shaft 101. In this instance the cap 703 also includes an upstanding member 705 which is affixed to the support beam 707 and assists with correctly orientating the beam during a seismic event.

[0089] Fig 7B depicts a further variation of the head assembly 700 of the present invention. In this particular example the head assembly 700 includes a plate 706 positioned on threaded rod 703 which is coupled to the upper end of the shaft 1011. The plate 706 is positioned on spring 702 and between nuts 7041, 704 ₂ . Again the rod 703 and nut 7041 are attached to a support beam 707. The plate 706 like the cap includes an upstanding member 705 which is affixed to the support beam 707 and assists with correctly orientating the beam during a seismic event. As in the case of Fig 7A the spring 702 in this example is of sufficient stiffness to permit the absorption of both longitudinal (i.e. lifting and down forces) and lateral shock imparted on the pile by the supported structure during a seismic event.

[0090] Figs 7C and 7D depict yet further arrangements of the head assembly 700 of the present invention. The example in fig 7C is of a similar construction to that of the head assembly in Fig 7A. As shown the head assembly of Fig 7C includes cap 701 positioned on spring 702 between nuts 704i, 704 ₂ mounted on threaded rod 703. The rod 703 and nut 704] are secured within a section of a concrete slab such as a perimeter beam or other such cast foundation (i.e. the foundation is cast about a portion of the head assembly).

[0091] Fig 7D depicts a head assembly of similar construction to that of Fig 7B and includes a plate 706 positioned on threaded rod 703 which is coupled to the upper end of the shaft 1011. The plate 706 is positioned on spring 702 and between nuts 704i, 704 ₂ . Again the rod 703 and nut 7041 are secured within a section of a concrete slab such as a perimeter beam or other such cast foundation (i.e. the foundation is cast about a portion of the head assembly).

[0092] Fig 8 shows a front view of a screw pile in accordance with another embodiment of the present invention. The screw pile 400 shown in figure 8 has a number of features in common with the screw piles shown in figures 1 to 7. For convenience, the common features will not be described in detail with reference to figure 8. The screw pile 400 shown in figure 8 includes twin blade sets, being a lower set of twin blades 402 and an upper set of twin blades 404. The blades are mounted on a shaft 406. Shaft 406 is made from a number of different shaft segments 408, 410. If it is designed to make the shaft 406 longer, additional shaft segments, such as the one shown at 412, can be included in the shaft. The shaft segment 410 includes a male connector 414 joined to the shaft segment at its lower end. The shaft segment 408 includes a female connector 416 joined to the shaft segment at its upper hand. To connect shaft segment 408 to shaft segment 410, it is a simple matter to threadably connect the male connector 414 to the female connector

416. Similarly, shaft segment 412 includes a female connector 418 at its upper end and a male connector 420 at its lower end. This facilitates easy connection of the shaft segment 412 into the shaft of the screw pile 400. [0093] It is advantageous to provide the screw pile with a shaft that is made from a number of shaft segments that are connected together. The lower shaft segment will typically carry the twin blade sets whilst the upper shaft segment will typically carry the lateral bracing fin assembly 422. If a longer shaft is required, one or more additional shaft segments can be connected into the intermediate part of the shaft. This allows the length of the shaft of the screw pile to be easily varied so that the length of the shaft of the screw pile can be set such that the twin blade sets extend below the liquefaction zone for a particular building site. For example, soils at one site may liquefy down to a depth of 10 m whilst soils at another site may liquefy down to 15 m. It is a simple matter to adjust the length of the shafts of the screw pile as shown in figure 8 to accommodate the different liquefaction depth requirements at each different site.

[0094] It is also possible to adjust or control the flexibility of the shaft by providing different length shaft segments. In this regard, the male and female connectors are, typically welded to the ends of the shaft segments and thus act as stiffeners or reinforcing members for the shaft segments. If a rigid shaft is required, the shaft segments may be relatively short. However, if a more flexible shaft is required, the shaft segments may be longer.

[0095] The lateral bracing fin assembly (stabiliser) 422 shown in figure 8 comprises three fins. The fins are equi-spaced and are spaced at 120° apart around the periphery. Three sleeves 424, 426, 428 are used to position the lateral bracing fin assembly 422 on the shaft. Collars (not shown in figure 8) are used to maintain the fin assembly 422 in position.

[0096] The screw pile 400 includes a free plate spring assembly 430 at its upper end. The spring assembly 430 allows a building element, such as a concrete slab or a floor joist, to be connected to the screw pile whilst also allowing for movement between the screw pile and the building in the event of an earthquake. The spring assembly 430 includes a lower plate 432 that is connected, such as by welding, to the upper part of shaft segment 410. A spigot spring 434 has an end 436 that passes through an opening 438 in the lower plate 432. The end 436 of the spring 434 is fusion welded to the lower plate 432. The spring 434 also includes an upper end 440 that passes through an opening 442 that is formed in an upper plate 444. The end 442 of the spring is fusion welded to the upper plate 444. In this manner, the spring 434 acts to space the upper plate 444 from the lower plate 432. This construction also allows the spring to freely move during an earthquake event without fouling on other components.

[0097] The spring 434 is suitably rated such that it has a higher rating than the weight of the building that is to be borne by the screw pile 400. For example, if the screw pile 400 is calculated Ί 9 to have to carry 5 tonnes when the building is completed, the spring 434 may be rated at, say, 7 tonnes. In this manner, compression of the spring is minimised or does not occur when the screw pile 400 is simply carrying the weight of the building. However, should an earthquake strike, some movement of the screw pile or the building may occur. This will inevitably involve some additional forces being imposed upon the spring 434. This will allow the spring 434 to bend or deform during an earthquake such that it dissipates some of the forces of the earthquake and also minimises movement of the building.

[0098] Figure 9 shows a view of the upper part of the screw pile 400 having a concrete slab thereon. A rod 450 is welded to the upper surface of the upper plate 444. Nut 450 is placed on the upper end of rod 450 and a pin or plate 454 is welded to the upper surface of the rod 450 and the nut 452. Appropriate concrete form work is positioned around the screw pile and a concrete slab 456 is poured such that the lower edge of the concrete slab rests on the upper surface of the upper plate 444. The slab 456 complete encases the pin or plate 454 to thereby connect the slab to the screw pile. It will be understood that other techniques may be used to connect a concrete slab to the upper end of the screw pile.

[0099] Figure 10 shows a beam 460, which forms a floor joist or a flooring beam of a building, being connected to the upper plate 444. In particular, the bean 460 comprises an I-beam and nuts and bolts 462, 464 extend through appropriate holes formed in the I-beam 460 and the upper plate 444 and connect the beam 462 the upper plate 444.

[00100] It will be appreciated that there are a number of alternative construction systems that use steel beams, timber beams or panels, any of which can be connected to the screw pile 400.

[00101] Figures 11 shows an exploded view of the upper part of shaft segment 408, the lower part of shaft segment 410, a male connector 414 and a female connector 416. As can be seen, the shaft segments 408, 410 comprise hollow, generally cylindrical steel shafts. The male connector 414 includes an outer region 500 that has substantially the same outer diameter as the shaft segment 410. The male connector 414 also includes two stepped down regions 502, 504. The stepped down regions are inserted into the open end of shaft segment 410 and the male connector 414 is then welded in position. The stepoed down regions act as a welding collar to assist in improving the quality of weld between the shaft segment 410 and the male connector 414. The male connector 414 also includes a screw thread extension 506. The interface region 508 is provided with a series of serrations or radially extending grooves, some of which are numbered at 510. [00102] The female connector 416 similarly includes an outer region 520 that has

substantially the same outer diameter as the outer diameter of the shaft segment 408. The female connector 416 also includes stepped down regions 522, 524. The stepped down regions of the female connector 416 are inserted into the open end of the shaft segment 408 and the female connector 416 is then welded to the shaft segment 408. The female connector 416 includes a flared end bolt entry hole 526 that provides entry to a threaded bore that can threadably receive the threaded extension 506 of the male connector 414. As the male connector is screwed into the female connector, the interface region 508 of the male connector comes into contact with the interface region of the female connector 416. The serrations or radial grooves 510 assist in locking the male connector to the female connector when the connection is torqued into place. To further assist in locking the interface regions together, the female connector may be provided with similar serrations or radial grooves (not shown) or, as shown in figure 11, or recessed website/logo/promotional information, which can also assist in interlocking the interfaces together.

[00103] The female connector 416 shown in figure 11 includes 4 drive lugs 530, 532, 534, 536. These drive lugs may be used instead of the drive lugs 407 shown in figure 8.

[00104] Figures 13 and 14 show another embodiment of a screw pile 600 in accordance with the present invention. Screw pile 600 includes lower twin blade set 604 and upper twin blade set 606 mounted on a shaft 608. The lower end of the shaft 608 may be provided with an attack bit. As shown in figure 14, lower blade set 606 includes blades 605, 607. Upper blade set 604 includes blades 601, 603. Of particular note in the embodiment shown in figures 13 and 14 is that the blades 601, 603 of the upper blade set 604 are larger than the blades 605, 607 of the lower blade set 606.

[00105] Figure 15 shows the screw pile 600 being installed in the ground. The upper end 610 of the screw pile 600 extends just above the ground level 612. A body of soil 614 is captured between the upper blade set 604 and the lower lead set 606 and is mobilised into a frusto-conical mass of soi 1 614 . This mass of soil is effectively trapped between the upper and lower blade sets. As a result, the outer surface of the mass of soil provides a large surface of trapped soil that acts as a friction surface to engage a relatively large body 616 of soil located in the vicinity of the screw pile 600. Without wishing to be bound by theory, the present inventors believe that this acts to spread the effective load imposed by the screw pile and carried by the soil over a larger volume of soil. Thus, the screw pile is less likely to sink into the soil, especially in regions where the soil is aerated or has low strength.

[00106] Reference throughout this specification to 'one embodiment' or 'an embodiment' means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases 'in one embodiment' or 'in an embodiment' in various places throughout this specification are not necessarily all referring to the same embodiment.

Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

[00107] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.