AU2012203161B2 - Screw pile - Google Patents

Abstract

A screw pile including a unitary elongate shaft having a central elongate axis with a pile head located at one end of the elongate shaft and a pile toe located at the other end and one or more screw formations fixed to said elongate shaft. The pile toe is in the form of an integrally formed penetrating formation that generally tapers inwardly from an outer peripheral surface of the shaft towards the central elongate axis. In the preferred from the pile toe is formed integrally at the end of a unitary shaft. The shaft is preferably of constant cross sectional shape. The integrally formed penetrating formation generally tapers inwardly from all points along an outer peripheral surface of the shaft towards the central elongate axis to ideally form a plurality of peripherally spaced elongate channels, each channel being tapered towards the central axis of said elongate shaft, disposed between a pair of elongate folds also being tapered towards the central axis of said elongate shaft. Fig. 2

Description

SCREW PILE

FIELD OF THE INVENTION

[0001 ] The present invention relates to screw piles and their construction.

[0002] The invention has been developed primarily as a screw pile for use in the construction industry and in particular for building construction and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this field of use. For example, the invention may be applied to a screw pile for the supporting of street signs, traffic lights, board walks, marina structures or other suitable applications.

BACKGROUND OF THE INVENTION

[0003] The following discussion of the prior art is intended to place the invention in an appropriate technical context and enable the associated advantages to be fully understood. However, any discussion of the prior art throughout the specification should not be considered as an admission that such art is widely known or forms part of the common general knowledge in the field.

[0004] Screw piles are used as anchor footings in the construction industry. They typically comprise an elongate steel shaft with a helical screw, or helix, fixed to the side of the shaft. A pile head adapted for torque transmitting connection to a prime mover is provided at one end of the elongate shaft and a pile toe for penetrating the ground is provided at the other end. In most cases the prime mover comprises a rotary hydraulic drive head fitted to suitable earth moving equipment which is selected according to the particular characteristics of the site and piles.

[0005] In order to install the screw pile into the ground, a rotational load or torque is applied to the pile head rotating it and causing the helical screw to bite into the ground in a similar manner to a self tapping screw. As the screw pile advances with each rotation, minimal spoil is generated. Throughout the installation process the torque resistance is measured and compared to a desired torque value. Rotation, vertical alignment and sometimes downward pressure are maintained until the screw pile is installed to the specified depth and torque. In these respects, rotation is generally applied until a torque value is achieved that is typically proportional to the pull-out force which the screw pile is required to resist. Once in place, the upper portion of the screw pile is fixed to the sub foundation system for the remaining construction to follow, as is commonly known in the art.

[0006] Once the screw pile has been properly inserted into the ground at the correct depth, the weight borne by the screw pile is distributed from the helical screw into the earth that lies underneath. The earth positioned above the helical screw assists in resisting any lifting forces applied to the screw pile and thereby maintains it in the ground. In this regard, screw piles are designed in accordance with specific installation requirements and the method by which the loads are to be transferred from the building via its foundations to the ground.

[0007] Screw piles may vary in shaft diameter, sectional length and in wall thickness where the shafts are hollow. The number, size and position of the helical screws may also vary in accordance with the site specific geotechnical requirements. However, in the majority of applications, the helix, or one of the helixes, is usually positioned adjacent the pile toe.

[0008] In some circumstances, it may transpire during design and/or installation, that in order to achieve the desired torque resistance, the screw pile has to go deeper than originally estimated, or achievable with a standard or previously specified length. For this reason, screw piles are typically adapted to receive supplemental extension shafts connectable to the pile head during installation. Normally, the extension shafts are welded or bolted in place thereby creating a segmented screw pile.

[0009] As mentioned earlier, during installation the downward movement is provided by the helical screw cutting in to and engaging the ground. However, it should be understood that in most cases it is the pile toe that penetrates the ground and performs the ground drilling to create the hole that accommodates the pile shaft. Accordingly, the function of the pile toe in a screw pile is significant to its installation in that, it must be shaped appropriately for the drilling process, whilst at the same time being strong enough to maintain its shape and operational effectiveness until the screw pile reaches the required depth.

[0010] To date various different forms of pile toes have been provided. In one known form, the elongate shaft is cut off at an angle thereby defining a pile toe in the form of an angled elliptical cutting edge at the end of the shaft. In another known form, the pile toe is in the form of a cutting blade or multiple cutting blades welded on to the end of the shaft. In another version the pile shaft is square cut at the end and squashed into a wide flat or s-shaped cutting blade. Other suggestions, not thought to have been used in the field, include the idea of somehow attaching separately formed smaller sectioned drilling formations to the pile screw shaft.

[0011] One problem that can occur during the installation of a screw pile, particularly where the pile toe is loaded unevenly due to encountering rocks or unexpected ground formations and/or where there is a weakness in the toe to shaft connection, is the potential deformation or fracture of the pile toe. If the pile toe does deform or even fracture during installation, the torque required to rotate the screw pile may vary unpredictably and, in some circumstances, prematurely reach the final torque value, thereby giving a false high reading and potentially undermining confidence in the foundation. In addition, any deformation or fracture of the pile toe may in turn cause deformation of other parts of the pile which could also compromise the structural integrity of the complete screw pile once installed.

[0012] It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

[0013] It is an object of a preferred form of the present invention to provide a screw pile that has a relatively stronger pile toe than prior art screw piles. It should also ideally penetrate the ground better and minimise the possibility of deformation of the pile toe during installation. The screw pile should be preferably simple and inexpensive to construct using as many standard components as possible.

SUMMARY OF THE INVENTION

[0014] According to a first aspect of the invention there is provided a screw pile including: an elongate hollow shaft having a central elongate axis; a pile head located at one end of said elongate shaft and a pile toe integrally formed at the other end; one or more screw formations fixed to said elongate shaft intermediate the pile head and the pile toe; and wherein said pile toe is integrally formed from said shaft hollow shaft to define a plurality of continuous contiguous folds and intermediate channels which all taper towards the central elongate axis to concentrate centrally at a distal end to thereby form a generally uniformly tapered penetrating formation.

[0015] While in a preferred embodiment the shaft is of unitary structure and constant cross sectional area throughout its length, in other embodiments the shaft may be of constant cross sectional shape, but varying cross sectional area, where, for example it may be desirable to swage downward the shaft size toward the pile toe, or construct the pile shaft from multiple lengths of shaft of the same sectional shape with the same or different sectional areas.

[0016] In one form, the pile toe includes seven elongate channels and folds.

[0017] In a preferred form, the pile toe has a generally frustoconical profile.

[0018] Preferably, the elongate shaft has a circular cross section throughout its working length although other cross sectional shapes may be suitable.

[0019] In the preferred forms, the pile has a head for engagement with a drive means that is in the form of a flared socket that can received a complimentary sized extension element if required. Preferably, the pile includes drive formations, ideally in the form of drive lugs, at or adjacent the pile head.

[0020] The pile toe is preferably formed by a single action swaging process whereby the toe end of the shaft is forced under pressure into a female die configured to create the tapered penetration formation defined in the preferred form by a series of flutes created by interconnecting tapered channels and folds.

[0021] After formation of the ends, the pile is completed by connection of one or more helix formations. Subject to site and performance requirements, the pile may be surface treated after completion.

[0022] Reference throughout this specification to “one embodiment”, “some embodiments” 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, appearances of the phrases “in one embodiment”, “in some embodiments” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] A preferred form of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: [0024] Figure 1 is a perspective view of a screw pile according to the invention; [0025] Figure 2 is a side view of the screw pile shown in Figure 1; [0026] Figure 3 is a top plan view of the screw pile shown in the previous Figures; [0027] Figure 4 is a side view of the screw pile of Figure 1, shown with an extension shaft installed; [0028] Figure 5 is a perspective view of a beam press suitable for forming the head and toe of the screw pile of Figure 1, illustrating loading of the hollow section from which the pile shaft is to be formed; [0029] Figure 6 is a perspective view of the beam press shown in Figure 6, illustrating the hollow section in the loaded position after the pile shaft is formed; [0030] Figure 7 is a top plan view of a die used to form the toe of the screw pile of Figure 1; [0031] Figure 8 is a perspective view of the pile shaft with integrally formed head and toe regions on removal from the press shown in Figures 5 and 6; and [0032] Figure 9 is a perspective view of the pile shaft of Figure 8 after welding on of the helix and drive lugs.

PREFERRED EMBODIMENTS OF THE INVENTION

[0033] Referring to the accompanying drawings and initially to Figures 1 to 5, there is provided a screw pile 1 according to the present invention. The screw pile includes a unitary elongate shaft 2 having a central elongate axis 3. A pile head 4, adapted for direct or indirect rotational coupling with a suitable prime mover, is located at one end of the elongate shaft 2 and a pile toe 5 for penetration with a ground surface, is located at the other end.

[0034] One or more screw formations 6, commonly referred to as helixes, are fixed to the side 7 of the elongate shaft 2 most usually by welding. The screw formations 6 are configured such that upon rotation of the screw pile about the axis 3, the screw pile 1 will penetrate a ground surface advancing with each rotation, without the need to exert a relatively excessive downward axial force.

[0035] According to the present invention, the pile toe 5 is in the form of an integrally formed penetrating formation 9 generally tapering inwardly from a starting point on an outer peripheral surface or circumference 10 of the pile shaft towards an end that closely surrounds the central axis 3. In other words, the tapering starts at all points on a circumference of the shaft 9 and moves inwardly towards the central axis 3. This is contrary to the most commonly used prior art pile toes which are formed by obliquely cutting the end of the shaft, integrally forming a relatively wide flat cutting formation at the end of the shaft which does not load evenly, or attaching separately made other cutting formations thereby introducing a potential weakness at the point of connection.

[0036] More particularly, in the illustrated embodiment, the pile toe 5 is in formed to define a plurality of circumferentially spaced elongate channels 11, each channel being disposed between a pair of elongate folds 12, which are crimped together at their distal ends 13. The channels and folds are contiguous and continuous and are each tapered towards the central axis 3 of the elongate shaft 2. Seven channels are shown, however, it will be appreciated that in other embodiments (not shown) three, four, five, six, eight, nine or more channels can be provided.

[0037] As mentioned earlier, the elongate shaft 2 is unitary in that it is formed from a single tubular member 20. Further, the unitary elongate shaft preferably has a constant cross sectional shape between the pile head 4 and pile toe 5. In the illustrated embodiment, the cross sectional shape is circular. However, in other embodiments (not shown), the shape could be octagonal, heptagonal, hexagonal, pentagonal, rectangular or triangular. Also, it should noted that whilst the shape is preferably maintained throughout the length of the shaft 2, the overall outer width and tube wall thickness may vary. For example, in some embodiments, it may be desirable to progressively step down the outer diameter of the shaft towards the toe region to create a smaller diameter penetrating length towards the toe, most usually with a corresponding increased wall thickness.

[0038] The method of forming the tapered flutes defined by channels 11 and folds 12 is discussed in detail below, however, it should be understood that the channels 11 and folds 12 are preferably continuous with no breaks or cut lines and formed by inwardly deforming the outer surface of the hollow shaft 2 towards and about its central axis 3.

In the preferred form no material is lost in the process of forming the channels and folds that define the pile toe.

[0039] A screw pile having this type of integrally formed pile toe 5 provides several advantages. Firstly, resistance to deformation of the pile toe is greatly improved because of the centrally tapering shape which means that the loading during installation, unlike much of the prior art, is evenly distributed. Furthermore, the process of formation of the toe results in a concentration of material at the tip where significant wear is likely to occur, as well as providing geometry that is stable and self- supporting.. Additionally, because the toe pile is cold formed, as further discussed below, it will have added strength because it is work hardened. Furthermore, as the pile toe is integrally formed and not separately attached, there are no concerns regarding possible detachment from the pile shaft. As a result of all these features the overall shape of the pile toe 5 is more likely to be maintained and its structural integrity is much less likely to be diminished during ground penetration. This in turn makes the operation of the pile easier to predict and provides increased confidence to structural engineers that specify this system.

[0040] The head 4 of the screw pile can take any suitable form. However, in the preferred embodiment, the head includes a flared socket 15 for receiving and connecting extension shafts and further includes radially outwardly extending drive lugs 19 via which torque is transferred from the rotary pile driver to the pile 1.

[0041] Whilst the downward movement of the screw pile is primarily provided by the screw formations 6 ‘screwing’ into the ground when rotated, the pile toe 5 configuration gives the screw pile 1 of the present invention an exceptional drilling or digging capacity, with the elongate channels 11 providing an ideal path for debris displacement.

The general shape of the pile toe 5 is easily adaptable to several different widths and/or diameters of elongate shaft providing the aforementioned advantages equally to each selected diameter.

[0042] According to the illustrated embodiment, the elongate shaft 2 has a circular tubular cross-section, generally of constant diameter and wall thickness between the pile head 4 and pile toe 5. Importantly, it will be appreciated that at a point adjacent tapered penetrating formation 9, the elongate shaft has a circular cross section thereby making each channel 11 and fold 12 generally equally shaped thereby minimising the possibility of stress concentrations.

[0043] That said, however, a generally even stress distribution may also be achieved using the aforementioned octagonal, heptagonal, hexagonal, pentagonal, rectangular or triangular tubular profiles as long as the number of channels provided corresponds to the outer profile .

[0044] In order to facilitate planned or unplanned axial extension of the elongate shaft 2 during the screw pile installation, the pile head 4 is in the form of a flared socket portion 15, which is adapted for complementary engagement with an extension shaft.

As shown in Figure 4, it is proposed that the flared portion 15 is sized for complementary fit and on-site welding with an extension shaft 16 of similar cross section to the elongate shaft 2. It is further proposed that, in line with normal practice, the extension shaft is connected to the pile head 4 at some point during the screw pile installation process. The extension shafts 16 usually have a straight cut unformed leading end that engages the socket 15 of the preceding pile 1 or preceding extension shaft, and a similar socket formation 15 with drive lugs 19 or other engagement means at the trailing end for attachment with the selected driver.

[0045] Contrary to other forms of extension shaft joining methods such as using keyed connections or threaded fasteners, this method provides a relatively stronger connection because the torque load is evenly distributed around the periphery of flared portion 15 and the strength of each element is not compromised by the need for notches or fastener penetrations. However, the invention is not limited to including this preferred form of connection.

[0046] The pile head is also configured to be engagable with prime movers such as screw pile drilling machines or excavators. In the preferred form illustrated, the pile head includes a plurality of drive lugs 19 which are welded to the flared socket portion. An adaptor (not shown) is then used to connect the pile screw to the rotary output on the pile driver. The adaptor includes formations to engage the drive lugs 19 on the pile head and includes means to engage and transmit torque from the driver output as is known in the art.

[0047] Referring to Figures 5 to 9 to construct the screw pile, the first step is to obtain a circular tube 40 of preselected material, diameter, wall thickness and length; these factors being selected based on the screw pile proposed load and installation requirements. In most cases the tubes will be made from a high carbon steel although other metals or other materials may be suitable. One embodiment designed to have a working load transfer capacity of 120kN uses a pile shaft made from CHS 101,4mm x 4.0mm Grade 350.

[0048] In the preferred form, a horizontal hydraulic beam press, such as that shown in Figures 5 and 6, is used to form the head 4 and toe 5 simultaneously. As will be seen from these Figures, one end of the tube 20 is pressed into a female die 22 to form or swage the inwardly tapered pile toe 5 according to the present invention, while the opposing end is slipped over a simple male die 24 which flares out the tube to form the pile head socket formation 15. In the illustrated form, the toe die 22 is located at the fixed end of the press against the frame 23 and the male die 24 is attached to the moving press ram 26. Furthermore, when producing long piles, intermediate tube supports may be included between the two operative ends of the press.

[0049] It will be appreciated that other press configurations could be used. Similarly, the pile head configuration can be varied from that described herein, and even when having a formed configuration, this need not be done at the same time as when the toe 5 is formed, although the advantages of doing this are clear.

[0050] Details of the female die 22 used to produce the pile in the drawings are shown in Figure 7. As can be seen the die has a complex cavity 25 that constitutes approximately the inverse shape of the circumferentially spaced and tapered elongate channels 11 and folds 12 that define the penetrating formation 9. In the illustrated form, this die 22 is produced by creating a thick sided ring formation 27 that defines a cylindrical cavity sized to receive the selected tube 20, with a series of equi-spaced tapered radially inwardly directed rounded forming blades 28 set into the inner surface 29 of the ring formation 27. Once the pile toe and head regions have been formed, the screw formations 6 and drive lugs 19 are then fixed in position by welding. The completed screw pile 1 can then be surface treated if required.

[0051] The extension pieces may be made in a similar manner, noting of course that in most instances a formed socket 15 and/or drive lugs 19 are only required at the trailing end depending upon intended application.

[0052] Advantageously, the process of forming the screw pile 10 is quick and easily repeatable. Also, the screw pile may be constructed using standard pre-cut raw tube sizes which are relatively inexpensive. Moreover, no machining is required thereby further reducing the cost of construction.

[0053] Furthermore, because the plastic deformation of the end of the raw tube 20 occurs at ambient temperature, a cold forming process is defined, as ambient temperature is below the re-crystallization temperature of carbon steel. Accordingly, the plastic deformation provides a work hardened pile toe 5.

[0054] The screw pile 10 of the present invention is installed in a similar way other screw piles known in the art. It is coupled to a prime mover, positioned and aligned at the point of installation and then rotated whilst maintaining the vertical alignment, thereby screwing itself into the ground surface. In most cases the pile of the present invention will have sufficient strength to be used without requiring any pre-treatment of the ground into which it is to be driven. However, in certain circumstances, as may be more common with existing piles, some degree of pre-drilling may be needed or desirable. Once in its final position, the pile head 4 can be fixed to a structure subfoundation as is known in the art.

[0055] It will be appreciated that the screw pile of the present invention provides a relatively stronger pile toe structure compared to other prior art screw piles. It is quick, easy and therefore relatively inexpensive to manufacture, primarily constructed from standard steel tubular sections, with no need to prepare and attach separately made cutting elements. Furthermore, while in the preferred embodiment the shaft is of unitary structure and constant cross sectional area throughout its length, in other embodiments the shaft may be of constant cross sectional shape, but varying cross sectional area, where, for example it may be desirable to swage downward the shaft size toward the pile toe, or construct the pile shaft from multiple lengths of shaft of the same sectional shape with the same or different sectional areas.

[0056] Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims (16)

1. CLAIMS:

   1. A screw pile including: an elongate hollow shaft having a central elongate axis, a pile head located at one end of said elongate shaft and a pile toe integrally formed at the other end; one or more screw formations fixed to said elongate shaft intermediate the pile head and the pile toe; and wherein said pile toe is integrally formed from said shaft hollow shaft to define a plurality of continuous contiguous folds and intermediate channels which all taper towards the central elongate axis to concentrate centrally at a distal end to thereby form a generally uniformly tapered penetrating formation.
2. 2. A screw pile according to any one of claims 1, wherein said pile toe includes seven elongate channels.
3. 3. A screw pile according to any one of claims 1 or claim 2, wherein said elongate channels are configured to provide a path for debris to travel upon penetration of said pile toe into a ground surface.
4. 4. A screw pile according to any one of the preceding claims wherein the elongate shaft has a circular cross sectional shape.
5. 5. A screw pile according to any one of claims 1 to 4, wherein the elongate shaft has a cross sectional shape which is octagonal, heptagonal, hexagonal, pentagonal, rectangular or triangular.
6. 6. A screw pile according any one of the preceding claims wherein said pile head is adapted for rotational coupling with a prime mover.
7. 7. A screw pile according any one of the preceding claims wherein said pile head is flared for complementary engagement with an extension shaft.
8. 8. A screw pile according any one of the preceding claims wherein said elongate shaft is formed from tubular steel.
9. 9. A screw pile according to any one of the preceding claims, wherein said pile toe is formed by pressing one end of said elongate shaft into one or more female dies in a swaging operation.
10. 10. A screw pile according to any one of the preceding claims wherein the pile toe has a generally frustoconical profile.
11. 11. A method of forming a screw pile in accordance with any one of the preceding claims, said method including the steps of: providing a raw hollow tube; pressing one end of said tube into a female die to form said pile toe; removing said tube from said female die; and fixing one or more screw formations to the side of said tube.
12. 12. The method of forming a screw pile according to claim 11, wherein said female die includes the, or a close approximation to, inverse shape of said integrally formed penetrating formation so as to enable formation of the pile toe in a single press operation.
13. 13. The method of forming a screw pile formation according to claim 11 or claim 12 including the additional step of pressing the end of said tube remote from the female die used to form the pile toe, into, or onto, another die to form a pile head formation for connection to a prime mover and/or pile extension shaft.
14. 14. The method of forming a screw pile of claim 13 wherein the pile toe and pile head are formed simultaneously in the one press apparatus.
15. 15. A screw pile substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.
16. 16. A method of manufacturing a screw pile substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.