FIELD OF THE INVENTION

This invention relates to screw piles. This invention has particular application to screw piles for providing load bearing piles for construction, and for illustrative purposes the invention will be described with reference to this application. However we envisage that this invention may find use in other applications such as supporting poles generally.

BACKGROUND OF THE INVENTION

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that the referenced prior art forms part of the common general knowledge in Australia.

Screw piles have found use since at last the early 19 ^th century in circumstances where conventional piles are difficult to foot in the foundation. Examples include jetty piles and the like where immersion, tidal conditions and ground conditions prevail against conventional piles. In more recent times screw piling has been developed for more general terrestrial piling applications. The field is well understood and various standard configurations of screw pile are routinely specified by engineers.

In Australian Patent 2003200645 there is provided a screw pile end piece having a cylindrical portion and an inwardly tapered portion at one end of the cylindrical portion and continuous with it. Part of a helical screw is formed on the cylindrical portion and part on said tapered portion. The helical screw is of constant pitch. The part of the helical screw on the cylindrical portion is of constant diameter and the part of the helical screw on the tapered portion has a minor radius coincident with the periphery of the tapered portion and a major radius greater than the minor radius. The width of the helical screw on the tapered portion between the minor radius and the major radius decreases towards the small end of the tapered portion. The constant diameter of the helical screw on the cylindrical portion is greater than about twice the diameter of the cylindrical portion per se. The stated advantage of the disclosed screw pile (over single turn welded plate helices on a tubular shaft) is that the load which can be applied to the shank can be transferred to the ground by the large diameter screw without undue distortion of the helical screw or shearing of the helical screw from the shank.

Apparatus in accordance with the foregoing prior art has the disadvantage that the point where the shear load on the pile while being driven is the part where the diameter of the helical screw is at least twice the diameter of the cylindrical portion. This ratio appears to be arbitrary and there is no stated reason for its selection. In any case, a mechanical disadvantage of the illustrated embodiments is excessive loading of the largest diameter portion of the helical flight.

SUMMARY OF THE INVENTION

In one aspect the present invention resides broadly in a screw pile including:

a body portion having an upper mounting portion configured to be axially attached to a pile tube and a lower portion tapering from said upper portion to form a penetrating end;

a substantially helical screw portion formed on said body and having a lead in portion toward said penetrating end and a trailing portion of selected maximum diameter; and

a bracing portion disposed between the upper mounting portion and the trailing portion.

The screw pile bit may be cast or fabricated. For example, the screw pile bit may be cast in steel. The bracing portion and upper mounting portion preferably support the trailing portion for at least half of the selected maximum diameter, in order to brace the most loaded part of the flight

The upper mounting portion configured to be axially attached to a pile tube may include a substantially cylindrical portion. The lower portion may taper from the upper portion to form the penetrating end. The lower portion may taper from the upper mounting portion to a substantially pointed end away from the upper mounting portion at a constant linear rate, at a variable rate such as to describe an axially curved surface, or in stages of differing taper. While the taper is preferably shallow adjacent the upper mounting portion, the helical screw flight strength rapidly increases away from the upper mounting portion as the diameter of the helical screw flight decreases, permitting the use of a deeper taper toward the substantially pointed end.

The mounting portion may be configured with a substantially cylindrical spigot portion bounded by an annular land. By this means a pile tube portion may be pushed over the spigot until the land in engaged, whereupon the full penetration field weld may secure the spigot, land and tube end. Alternatively, the mounting portion may be configured with an internal bore having engagement means adapted to selectively engage corresponding engagement means provided on the outer surface of a pile portion end. The engagement means in the internal bore may be located to be supported against distortion of the bore by a reinforcing collar. Particular configurations of interconnection are described hereinafter.

Alternatively, the mounting portion may comprise an elongate spigot cast integrally with the axial body portion and adapted to receive the hollow annular end of a cylindrical hollow section (CHS) pile. The annular end may abut a reinforcing collar portion of the axial body as a land. An axial bore of the elongate spigot may be polygonal in section to form a drive socket for engagement by a corresponding drive element located in the bore of the CHS pile. The CHS pile may be secured to the spigot by means such as blind rivets to minimise interference with the polygonal bore. The drive socket is preferably hexagonal in section, to balance the bearing capacity of the flats with the minimum wall thickness of the spigot.

The helical screw flight may have a diameter that is decreasing with the taper of the axial body portion and does not require a single revolution of constant diameter to reach its specified holding. The pitch of the screw flight may be determined empirically having regard to the substrate and driving torque to be applied. An arbitrary indication for a wide range of soil types is a pitch of about 25% of the largest diameter of the helical screw flight. The helical screw flight may comprise a single turn in the manner of a plate helix screw pile. Single-turn plate-like screw piles in accordance with the present invention may be provided with a cutting edge on the leading edge of the flight.

The bracing portion disposed between the upper mounting portion and the trailing portion may comprise a cast-in buttress portion stiffening the junction between the helical screw flight and the body portion. The buttress may be confined to the trailing portion or may extend substantially down the helical screw flight toward the leading portion. The buttress may progressively reduce in bulk and section leading away from the trailing portion, and may vanish at a selected distance down the flight from the trailing portion.

The bracing portion may include an extension of the trailing edge essentially extending the helical screw up the mounting portion at reducing diameter and the same pitch as the helical screw flight. In the lower limit this form of bracing may comprise an asymptote-edged flight extension extending up the mounting portion trailing edge for half a turn or so. In the upper limit the bracing portion may include one or mor turns of upwardly diminishing diameter. Bracing portions of this form have the added advantage of assisting in backing out of a pile which would otherwise stall on backing out.

The bracing portion may comprise a substantially cylindrical reinforcing collar adjacent the mounting portion. In this embodiment the axial body portion may taper from the reinforcing collar to a substantially pointed end away from the reinforcing collar. A helical screw flight of substantially constant pitch may extend from a securing point at the reinforcing collar toward the substantially pointed end. The diameter of the helical screw flight may again decrease with the taper of the axial body portion to terminate adjacent the pointed end. The reinforcing collar may strengthen the area of insertion of the CHS pile.

The substantially cylindrical reinforcing collar may be of any axial extent consistent with supporting the mounting portion and providing an anchor of sufficient axial extent to support the maximum diameter of the helical screw flight against distortion under driving loads. The minimum axial extent may be determined with reference to the ratio of the collar diameter and screw flight diameter, as well as the yield strength of the material of the collar in bending and the helical screw flight in shear. A guide to a minimum axial dimension of the reinforcing collar, for a unitary cast steel bit where the collar diameter supports 52% of the helical screw flight diameter, is about 10% of the screw flight diameter at the reinforcing collar.

The reinforcing collar may be of a diameter selected to support at least half of the overall diameter of the helical screw flight at the reinforcing collar. The final selection of collar diameter may be determined empirically having regard to the competing imperatives of having a minimum transverse cross section while supporting the largest diameter of the helical screw flight to the greatest radial extent.

The reinforcing collar may be provided with a transitional portion tapering to the diameter of one or both of the mounting portion and the axial body portion. Particular advantage in engagement of the helical screw flight and the reinforcing collar is provided where the helical screw flight is secured about a circumferential extent of the transition portion, to terminate at the reinforcing collar.

In the driving of screw piles, the traditional method of joining pipe lengths is to field weld a drive spider of flat bar to reinforce the join followed by butt welding the adjacent pipe ends. Australian patent 2003200645 discloses incidentally a coupling arrangement where a female coupling part has a plurality of protrusions pressed into and out of the notional bore to provide a series of three axially spaced circumferential recesses interconnected by an axially directed slot opening to the coupling free end. A corresponding male part has three lugs each corresponding to a particular one of the three axially spaced circumferential recesses. The axially directed slot opening to the coupling free end is located between the recess ends such that it remains engaged with the male part while either driving or reversing out. The arrangement is somewhat weak and unable to deal with high driving and backing out loads

In a further aspect there is provided a coupling for interconnection screw pile pipe components and including a cast female coupling part having an axial bore and including a mounting portion adapted to be secured to the plain end of a pile pipe element, an inner reinforcing collar portion adjacent the mounting portion, a substantially cylindrical body portion extending from the reinforcing collar portion, and an outer reinforcing collar portion, the inner and outer reinforcing collars backing integrally cast lugs formed on the wall of the bore, and a cast male coupling part including a mounting portion adapted to be secured to the plain end of a pile pipe element and having an outer substantially cylindrical surface having recessed portions adapted to be engaged by said lugs, the lugs and recesses being configured to allow axial insertion of the male coupling part into the bore followed by rotation into torque transmitting engagement whereupon axial disengagement is prevented.

The lugs and recesses may be configured to interengage against axial separation on both driving and backing out. In the alternative or in addition there may be provided corresponding transverse bores adapted to receive a transverse locking pin securing the coupling together against separation on backing out.

In other embodiments cast steel connector portions may be provided with a stepped mandrel type ends providing for field welding to any one of a range of pile diameters. In yet further embodiments, connectors in cast steel are formed as axially engagable spigot and socket bodies, the respective bodies having corresponding transverse bores to allow the connectors to be secured together for transmission of torque by one or more substantial drive pins. The free ends of the respective bodies may be formed as a stepped spigot to permit insertion into a range of pile CHS for welding

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described with reference to the following non-limiting embodiment of the invention as illustrated in the drawings and wherein:

Fig. 1 is a plan view of a screw pile bit in accordance with the present invention;

Fig. 2 is a side elevation of the apparatus of Fig. 1 ;

Fig. 3 is a section A-A of a female coupling for use in the pile string which engages the apparatus of FIG. 1 , and

Fig. 4 is a side view of the female coupling of FIG. 3;

Fig. 5 is a perspective view of the female coupling of FIG. 3;

Fig. 6 is a section B-B of the female coupling of FIG. 3;

Fig. 7 is a section A-A of a male coupling to connect the pile string to the female coupling of Figs. 3 to 6;

Fig. 8 is a side view of the male coupling of FIG. 7;

Fig. 9 is a perspective view of the male coupling of FIG. 7,

Fig. 10 is a section B-B of the female coupling of FIG. 7;

Fig. 1 1 is a plan view of an alternative embodiment of the invention; and

Fig. 12 is a side view of the apparatus of Fig. 1 1

In the embodiment of Figs 1 and 2, there is provided a screw pile bit comprising a unitary hollow-cast steel unit having a tapered body 10, a stepped mounting portion 1 1 , a reinforcing collar 12 and a helical flight 13. The tapered body 10 has an upper tapered portion 14 of shallow taper and a lower tapered portion 15 of sharper taper converging to a penetrating point 16. The penetrating point 16 includes a cutaway 17 penetrating into the hollow of the bit and providing a void vent during casting while improving start up bite in use.

The stepped mounting portion 1 1 includes two spigot portions 20 adapted to pass into selected CHS pile pipe ends and are bounded by respective tapered lands 21 to which a respective CHS pipe end may be welded.

The reinforcing collar 12 has a centre section 22 with an upper transition taper 23 to the stepped mounting portion 1 1 . The upper transition taper 23 forms a land to which oversize pile CHS can be welded. A lower transition taper 24 grades the transition from the reinforcing collar 12 to the upper tapered portion 14 via a fillet 25.

The helical flight 13 has a maximum diameter at its upper turn 26. At this point the diameter of the reinforcing collar is 52% of the maximum diameter. This provides sufficient bracing while minimizing the dead plug effect of the collar. The upper trailing edge 27 of the upper turn 26 is curved to assist in backing out. The upper turn 26 is formed integrally with the reinforcing collar 12 and transitions to the upper tapered portion 14. The loading of the line joining the flight 13 and the reinforcing collar 12, the lower transition taper 24, the upper tapered portion 14 and the lower tapered portion 15 is controlled by cast-in fillets 30. The helical flight 13 tapers in substantial proportion to the respective tapers of the tapered body 10.

Piling of cylindrical hollow section CHS is supplied in unit lengths. Piling may require multiple lengths to be joined together.

Figs. 3 to 6 illustrate a cast steel female connector having a substantially cylindrical hollow body 31 having an internal bore 32. Within the bore 32 are located two annular, spaced arrays of four lugs 33. One end 34 of the body 31 is open to receive a male connector. The other end comprises an integral stepped mounting portion 35 including two spigot portions 36 adapted to pass into selected CHS pile pipe ends and bounded by respective tapered lands 37 to which a respective CHS pipe end may be welded.

A reinforcing collar 40 has a centre section 41 with an outer transition taper 42 to the stepped mounting portion 35. The outer transition taper 42 forms a land to which oversize pile CHS can be welded. An inner transition fillet 43 grades the transition from the reinforcing collar 40 to the cylindrical hollow body 31 . The open end 34 is stiffened by a further integrally cast external reinforcing collar. Multipurpose transverse bores 45 provide for a tommy bar to apply torque by hand, or drive pins (not shown) securing the male and female connectors. Figs. 7 to 10 illustrate a cast steel male connector having a substantially cylindrical hollow body 46 having an internal bore 47. Cast into the outer surface of the substantially cylindrical hollow body 46 are four shaped recesses 47. One end 50 of the body 46 is plain to enter the bore 32 of the female connector. The other end comprises an integral stepped mounting portion 51 including two spigot portions 52 adapted to pass into selected CHS pile pipe ends and bounded by respective tapered lands 53 to which a respective CHS pipe end may be welded.

The recesses 47 have a lead in passage 54into which the lug 33 of the female connector may pass until the respective lugs are adjacent locating recesses 55. Thereafter, relative rotation of the connectors locates the lugs 33 in one or the other pair of the recesses 55, depending on whether the pile is being driven or backed out. Transverse drilling 56 is positioned whereby it aligns with one or another of the pair of multipurpose transverse bores 45 when the connectors are locked up, a drive pin (not shown) optionally securing the male and female connectors.

A reinforcing collar 57 braces the stepped mounting portion 51 . The outer tapered land 53 is the transition to the collar 57 and is a land to which oversize pile CHS can be welded.

In the alternative embodiment of Figs. 1 1 and 12, where like components are numbered the same as in Figs. 1 and 2, there is provided a screw pile bit comprising a unitary hollow-cast steel unit having a tapered body 10, a stepped mounting portion 1 1 and a helical flight 13. The tapered body 10 has an upper tapered portion 14 of shallow taper and a lower tapered portion 15 of sharper taper converging to a penetrating point 16. The penetrating point 16 includes a cutaway 17 penetrating into the hollow of the bit and providing a void vent during casting while improving start up bite in use.

The stepped mounting portion 1 1 includes two spigot portions 20 adapted to pass into selected CHS pile pipe ends and are bounded by respective tapered lands 21 to which a respective CHS pipe end may be welded. The helical flight 13 has a maximum diameter at an intermediate turn at 26. The upper trailing edge 27 of the intermediate turn 26 passes into a helical extension 60 of reducing diameter, which diminishes to zero width in about one turn at 61 . This configuration braces the intermediate turn 26 as well as providing for positive backing out if required.

It will of course be realised that while the above has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as is set forth in the claims appended hereto.