Title:
Screw piles
Kind Code:
A1


Abstract:
A screw pile stem includes a shank having an inwardly tapered portion at one end, and a helical screw on the shank, with the helical screw being of constant pitch and at least a part of the helical screw being on the tapered portion, and with a major diameter of the part of the helical screw on the tapered portion decreasing towards a small end of the tapered portion.



Inventors:
Camilleri, Paul Anthony (Mermaid Beach, AU)
Application Number:
10/683409
Publication Date:
04/22/2004
Filing Date:
10/09/2003
Assignee:
CAMILLERI PAUL ANTHONY
Primary Class:
Other Classes:
52/169.13, 405/251
International Classes:
E02D5/56; E02D27/16; (IPC1-7): E02D5/08; E02D27/42
View Patent Images:



Primary Examiner:
SAFAVI, MICHAEL
Attorney, Agent or Firm:
ABELMAN, FRAYNE & SCHWAB (666 THIRD AVENUE, 10TH FLOOR, NEW YORK, NY, 10017, US)
Claims:

What is claimed is:



1. A screw pile stem comprising: a shank having an inwardly tapered portion at one end; and a helical screw on the shank, the helical screw being of constant pitch and at least a part of the helical screw being on the tapered portion, a major diameter of the part of the helical screw on the tapered portion decreasing towards a small end of the tapered portion.

2. The screw pile stem according to claim 1, wherein the shank has a generally cylindrical portion coaxial with and/or adjacent to the tapered portion and a part of the helical screw is on the generally cylindrical portion.

3. The screw pile stem according to claim 2, wherein the part of the helical screw on the cylindrical portion extends about one full turn.

4. The screw pile stem according to claim 1, wherein the part of the helical screw on the tapered portion extends at least one full turn.

5. The screw pile stem according to claim 1, wherein the major diameter of the part of the helical screw on the tapered portion generally decreases at a constant rate.

6. The screw pile stem according to claim 1, wherein the major diameter of the part of the helical screw on the tapered portion generally decreases at the same rate as the diameter of the tapered portion.

7. The screw pile stem according to claim 1, wherein the shank includes: a body portion; and an end portion coupled to the body portion at one end thereof.

8. The screw pile stem according to claim 7, wherein the tapered portion is on the end portion.

9. The screw pile stem according to claim 7, wherein the end portion includes a cylindrical portion and a part of the helical screw is on the cylindrical portion.

10. The screw pile stem according to claim 7, wherein all of the helical screw is on the end portion.

11. The screw pile stem according to claim 7, wherein the body portion and the end portion include complementary coupling means by which the end portion is detachably coupled to the body portion.

12. The screw pile stem according to claim 11, wherein the complementary coupling means are adapted to transmit forward and reverse rotational drive from the body portion to the end portion.

13. The screw pile stem according to claim 12, wherein the cylindrical portion forms a socket on the end portion; and wherein the body portion includes a spigot which is engaged in the socket, one of the socket and the spigot having a side wall with a protuberance thereon and the other of the socket and the spigot having a side wall with a complementary recess therein adapted to receive the protuberance, the protuberance being adapted to engage in the recess so as to transmit forward and reverse drive to the end portion.

14. The screw pile stem according to claim 12, wherein the cylindrical portion forms a spigot on the end portion, the body portion includes a socket, and the spigot is engaged in the socket, one of the socket and the spigot having a side wall with a protuberance thereon and the other of the socket and the spigot having a side wall with a complementary recess therein adapted to receive the protuberance, the protuberance being adapted to engage in the recess so as to transmit forward and reverse drive to the end portion.

15. The screw pile stem according to claim 13, wherein one of the socket and the spigot has a side wall with a plurality of protuberances thereon, and the other of the socket and the spigot has a side wall with a complementary recess therein adapted to receive the protuberances, the protuberances being adapted to engage in the recess so as to transmit forward and reverse drive to the end portion.

16. The screw pile stem according to claim 13, wherein each of the spigot and the socket terminates at a free end, the recess opens to a respective one of the free ends, and each protuberance is adapted to enter and exit the recess through the opening to the free end upon relative axial movement of the spigot and socket.

17. The screw pile stem according to claim 16, wherein the recess includes two circumferentially spaced-apart securing portions adapted to selectively receive therein a protuberance in which relative axial movement between the spigot and the socket is prevented.

18. The screw pile stem according to claim 17, wherein the opening is between the circumferentially spaced-apart securing portions.

19. The screw pile stem according to claim 18, wherein the recess has a plurality of spaced-apart axially-aligned securing portions, one of the spigot and the socket has a plurality of axially-aligned protuberances, and the protuberances are arranged to coincidentally locate in respective ones of the securing portions to prevent relative axial movement between the spigot and the socket.

20. The screw pile stem according to claim 13, wherein at least one of the recesses is formed by pressing a portion of the side wall inwards.

21. The screw pile stem according to claim 13, wherein partial relative rotation of the spigot and socket causes each protuberance to locate in one of the respective securing portions.

22. The screw pile stem according to claim 21, wherein each protuberance and recess are arranged such that partial relative rotation of the spigot and the socket urges the end portion and the body portion axially together.

23. The screw pile stem according to claim 13, further comprising: a plurality of complementary circumferentially spaced-apart protuberances and recesses.

24. The screw pile stem according to claim 13, wherein the socket has a shoulder therein, and the end of the spigot is adapted to abut the shoulder, whereby downward loads applied to the upper end of the shank are transmitted to the helical screw by the shoulder.

25. The screw pile stem according to claim 1, wherein the shank includes extension coupling means at its other end for coupling thereto an extension stem.

26. The screw pile stem according to claim 25, wherein the extension coupling means is adapted to engage complementary coupling means on an extension stem corresponding to the coupling means on the one end.

27. A screw pile end piece adapted to be connected to a pile stem, the screw pile end piece comprising: an inwardly tapered portion with at least a part of a helical screw thereon, the helical screw on the tapered portion being of constant pitch and a major diameter of the helical screw decreasing towards a small end of the tapered portion.

28. The screw pile end piece according to claim 27, further comprising: a generally cylindrical portion coaxial with and adjacent to the tapered portion; and wherein part of the helical screw is on the generally cylindrical portion.

29. The screw pile end piece according to claim 28, wherein the part of the helical screw on the cylindrical portion extends about one full turn.

30. The screw pile end piece according to claim 27, wherein the part of the helical screw on the tapered portion extends at least one full turn.

31. The screw pile end piece according to claim 27, wherein the major diameter of the part of the helical screw on the tapered portion generally decreases at a constant rate.

32. The screw pile end piece according to claim 27, wherein the major diameter of the part of the helical screw on the tapered portion generally decreases at the same rate as the diameter of the tapered portion.

33. The screw pile end piece according to claim 27, further comprising: coupling means adapted to engage complementary coupling means on a pile stem to which the end piece is to be attached for coupling the screw pile end piece thereto, with the coupling means being adapted to receive forward and reverse rotational drive from the complementary coupling means of the pile stem.

34. The screw pile end piece according to claim 33, wherein the cylindrical portion forms a socket which is adapted to receive therein a complementary spigot on the pile stem to which the end piece is to be coupled, with the socket having a side wall with a protuberance thereon adapted to engage in a complementary recess in the pile stem, or a recess therein adapted to receive a complementary protuberance on the pile stem so as to receive forward and reverse drive therefrom.

35. The screw pile end piece according to claim 33, wherein the cylindrical portion forms a spigot which is adapted to engage in a complementary socket on the pile stem to which the end piece is to be coupled, the spigot having a recess therein adapted to receive a complementary protuberance in the socket, or the spigot having a protuberance thereon adapted to engage in a complementary recess in the socket of the pile stem, so as to receive forward and reverse drive therefrom.

36. The screw pile end piece according to claim 34, wherein the socket has a side wall with a plurality of protuberances thereon adapted to engage in a complementary recess in the pile stem so as to receive forward and reverse drive therefrom.

37. The screw pile end piece according to claim 34, wherein the spigot terminates at a free end and the recess opens to the free end, the opening being adapted to receive therethrough the protuberance of the pile stem to which the end piece is to be coupled.

38. The screw pile end piece according to claim 34, wherein the socket terminates at a free end and the recess opens to the free end, the opening being adapted to receive therethrough the protuberance of the pile stem to which the end piece is to be coupled.

39. The screw pile end piece according to claim 37, wherein the recess includes two circumferentially spaced-apart securing portions adapted to selectively receive therein a protuberance such that relative axial movement between the pile stem and the end piece is prevented.

40. The screw pile end piece according to claim 39, wherein the opening is between the circumferentially spaced-apart axially-aligned securing portions.

41. The screw pile end piece according to claim 40, wherein the recess has a plurality of spaced-apart axially-aligned securing portions.

42. The screw pile end piece according to claim 34, wherein the recess extends only partway through the side wall of the socket.

43. The screw pile end piece according to claim 35, wherein the recess extends only partway through the spigot.

44. The screw pile end piece according to claim 36, wherein the plurality of spaced-apart protuberances are axially-aligned and adapted to engage in complementary securing portions of a recess in the pile stem to which it is to be coupled.

45. The screw pile end piece according to claim 34, wherein the socket has a shoulder therein adapted to be engaged by the free end of the pile stem to which the shoulder is to be attached and to receive bearing loads therefrom.

46. The screw pile end piece according to claim 35, wherein the spigot has a shoulder thereon adapted to be engaged by the free end of the pile stem to which the shoulder is to be attached and to receive bearing loads therefrom.

47. The screw pile end piece according to claim 34, wherein the recess is formed by pressing a portion of the side wall inwards.

48. A pile stem for screw piles, the pile stem comprising: a body portion; and two opposite end portions, with: a first end portion being adapted to engage a first screw pile end piece having an inwardly tapered portion with at least a part of a helical screw thereon, the helical screw on the tapered portion being of constant pitch and a major diameter of the helical screw decreasing towards the small end of the tapered portion; and a second end portion being adapted to engage a second like pile stem.

49. In combination, a screw pile assembly comprising: a screw pile end piece having an inwardly tapered portion with at least a part of a helical screw thereon, the helical screw on the tapered portion being of constant pitch and a major diameter of the helical screw decreasing towards a small end of the tapered portion; and a pile stem adapted to be detachably coupled to the screw pile end piece.

50. A screw pile stem comprising: a steel stem; and a cast end piece secured thereto.

51. A screw pile end piece comprising: a body formed of cast steel.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to screw piles and components for screw piles. The invention has particular application to screw piles for the construction of dwelling houses and small commercial buildings but it may be useful for larger buildings and other structures.

[0003] 2. Description of the Related Art

[0004] Screw piles for houses typically are made up of a base stem (or a screw pile stem) and a plurality of extension stems. Typically, the base stem has a tubular steel shank with one flight (that is, one turn) of a helical screw welded thereto adjacent its lower end for screwing the pile into the ground upon rotation by suitable screw piling apparatus and a coupling portion at its upper end which is adapted to engage a complementary coupling portion of an extension stem. Typically, a plurality of extension stems can be added, one to another, to effectively form a pile of any desired length which can be screwed into the ground to any desired depth with each extension stem having a coupling portion similar to that of the base stem. Various types of complementary coupling portions which together form a coupling are known.

[0005] The single turn helical screw is typically formed from steel plate and the minor diameter of the screw is substantially the same as the outside diameter of the steel shank to which it is welded while the major diameter is considerably greater and could be three or four times the minor diameter and possibly even more.

[0006] The helical screw of such known screw piles is the main portion which transfers the building load applied to the upper end of the pile to the founding ground. One disadvantage with such screw piles is that in some cases the load which can be applied to the tubular steel shank cannot be transferred to the ground by the large diameter steel plate screw. For example, the steel shank may have a structural capacity of about 1,000 kN. while the steel plate screw may suffer unacceptable distortion under a shank load of only 500 kN. or shear from the shank or deformation of the shank at the welded joint between the screw and the shank.

[0007] Another disadvantage with known screw piles is that in many cases the couplings by which adjacent stems are connected to each other are generally not capable of both withstanding the torsional forces required to screw the pile to the desired founding depth and transmitting the building load applied to the upper end of the top pile stem to the next pile stem and so on without an undesirable amount of failure.

[0008] Another disadvantage with known screw piles is that damaged pile stems cannot be easily removed and replaced.

BRIEF SUMMARY OF THE INVENTION

[0009] One object of the present invention is to provide a screw pile which overcomes or at least ameliorates one or more of the aforementioned problems.

[0010] With the foregoing in view the invention resides broadly in one aspect in a screw pile stem including:

[0011] a shank having an inwardly tapered portion at one end; and

[0012] a helical screw on the shank, the helical screw being of constant pitch and at least a part of the helical screw being on the tapered portion, the major diameter of the part of the helical screw on the tapered portion decreasing towards the small end of the tapered portion. Preferably, the part of the helical screw on the tapered portion extends at least one full turn.

[0013] Preferably, a generally cylindrical portion is provided coaxial with and/or adjacent to the tapered portion and part of the helical screw is on the generally cylindrical portion. In such form of the invention, while it is preferred that the part of the helical screw on the cylindrical portion extends about one full turn of constant major diameter, it is also preferred that the major diameter of the part of the helical screw on the tapered portion generally decreases at a constant rate. It is also preferred that such part of the helical screw generally decreases at the same rate as the diameter of the tapered portion, that is, the major and minor diameters decrease at the same rate such that where the diameter of the tapered portion is half that of the cylindrical portion, the major diameter of the screw is half that of the screw on the cylindrical portion.

[0014] Preferably, said shank includes a body portion and an end portion, and the end portion is connected to the body portion at one end. In such form it is preferred that the end portion is cast steel or other suitable material.

[0015] In another aspect the invention resides broadly in a screw pile end piece adapted to be connected to the pile stem, the screw pile end piece having an inwardly tapered portion with at least a part of a helical screw thereon, the helical screw on the tapered portion being of constant pitch and the major diameter of the helical screw decreasing towards the small end of the tapered portion. Preferably, the end piece includes a generally cylindrical portion coaxial with and/or adjacent to the tapered portion and part of the helical screw is on the generally cylindrical portion. It will be appreciated that such a screw pile end piece may be connected to a pile stem to form a screw pile stem as previously described. Advantageously, in a preferred form, all of the helical screw is on the end piece which allows the pile stem which forms the shank to be a simple tubular stem with connecting means at one end for connecting to the end piece. Such a stem can be a pile extension stem adapted to couple to other like extension stems thus limiting the type of stock to be held. Further, such arrangement allows the stems to be stored and transported as a bundle of tubes with the end pieces as separate components, thus allowing easier and closer stacking, making transport easier and more efficient.

[0016] Preferably, the end piece and the pile stem to which it is to be connected include complementary coupling means which allow the pile stem to be detachably coupled to the end piece. Advantageously, such arrangement has the further advantage that a damaged pile stem can be detached from an end piece and withdrawn from a pile hole during installation while leaving the end piece in situ and then a new pile stem may be fitted to the end piece down the hole.

[0017] In another aspect the invention resides broadly in the combination of an end piece as previously described and a pile stem adapted to be detachably coupled to the end piece. Preferably, the complementary coupling means are adapted to transmit forward and reverse rotational drive from the pile stem to the end portion.

[0018] In a preferred form, the cylindrical portion forms a socket on the end piece, and the pile stem includes a spigot which is adapted to be engaged in the socket, one of the socket and the spigot having a side wall with a protuberance thereon and the other of the socket and the spigot having a side wall with a complementary recess therein adapted to receive the protuberance, the protuberance being adapted to engage in the recess so as to transmit forward and reverse drive to the end piece. However, in another form the spigot and socket are reversed so that the cylindrical portion forms the spigot on the end piece and the pile stem includes the socket.

[0019] In one form, the socket has a side wall with a plurality of protuberances thereon adapted to engage in a complementary recess in the spigot. In such form the spigot terminates at a free end and the recess opens to the free end, the opening being adapted to receive therethrough the protuberance on the side wall of the socket as the spigot and socket move into axial engagement. However, in another form, the recess is formed in a wall of the socket which terminates at a free end and the recess opens to the free end, the opening being adapted to receive therethrough the protuberance which is provided on a side of the spigot.

[0020] Preferably, the recess includes two circumferentially spaced apart securing portions adapted to selectively receive therein a protuberance such that relative axial movement between the pile stem and the end piece is prevented. In such form it is preferred that the opening is between the circumferentially spaced apart securing portions. It is also preferred that the recess has a plurality of spaced apart axially aligned securing portions. In the case where the recess is provided in the side wall of the socket it is preferred that the recess extends only partway through the side wall of the socket. In a preferred form, the recess is formed by pressing the wall of the socket inwards thus maintaining the full wall thickness of the socket through the full extent of its circumference.

[0021] Preferably, the plurality of spaced apart protuberances are axially aligned and adapted to engage in complementary securing portions of the recess.

[0022] Preferably, the socket has a shoulder therein adapted to be engaged by the free end of the spigot so that bearing loads can be transferred from the pile stem to the end piece by the shoulder. In one form where the socket is provided on the end piece, the shoulder is in the end piece while in another form in which the socket is provided on the pile stem, the shoulder is in the pile stem. Preferably, the coupling means are arranged to urge the free end of the spigot into engagement with the shoulder upon relative movement of the pile stem and the end piece into the coupled position.

[0023] In another aspect the invention resides broadly in a pile stem for screw piles, the pile stem having a body portion and two opposite end portions, one end portion being adapted to engage a screw pile end piece as previously described and the other end being adapted to engage another like pile stem.

[0024] In another aspect the invention resides broadly in the combination of an end piece and a pile stem as previously described.

[0025] The terms “upper”, “lower”, “top”, “bottom”, “side”, “forward”, “reverse” and the like are used herein to describe screw pile stems and components therefor in their normal in-use position and are not intended to limit the use of the invention to any particular orientation. Further the terms “forward” and “reverse” are used to describe the direction of rotation of the screw piles into and out of the ground respectively.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0026] In order that the invention can be more easily understood and put into practical effect, reference will now be made to the accompanying drawings, wherein:

[0027] FIG. 1 is an elevational view of a screw pile stem and extension stem according to the invention in-line for assembly, with inserts A and B shown in greater detail in FIGS. 1A-1B, respectively;

[0028] FIG. 2 is an end view of the screw pile stem shown in FIG. 1;

[0029] FIG. 3 is an end view of the extension stem shown in FIG. 1;

[0030] FIG. 4 is a sectional elevational view of the upper end portion of the screw pile stem shown in FIG. 2 along lines 4-4 in cut-away;

[0031] FIG. 5 is a sectional elevational view of the lower end portion of the extension stem shown in FIG. 3 along lines 5-5 in cut-away;

[0032] FIG. 6 is a pictorial representation of a screw pile end piece according to the invention;

[0033] FIG. 7 is an elevational view of the screw pile end piece of FIG. 6 from one side;

[0034] FIG. 8 is an elevational view of the screw pile of FIG. 6 at 90 degrees to the elevational view of FIG. 7;

[0035] FIG. 9 is a top end view of the screw pile end piece of FIG. 6, with insert A shown in greater detail in FIG. 9A;

[0036] FIG. 10 is a sectional elevational view of the screw pile end piece of FIG. 6 along lines 10-10;

[0037] FIG. 11 is a pictorial representation of an extension stem according to the invention;

[0038] FIG. 12 is an upper end view of the extension stem of FIG. 11;

[0039] FIG. 13 is a lower end view of the extension stem of FIG. 11;

[0040] FIG. 14a is an elevational view of the upper end portion of the extension stem of FIG. 11;

[0041] FIG. 14b is a sectional elevational view of the upper end portion of the extension stem of FIG. 11 along lines 14-14;

[0042] FIG. 15a is an elevational view of the lower end portion of the extension stem of FIG. 11;

[0043] FIG. 15b is a sectional elevational view of the lower end portion of the extension stem of FIG. 11 along lines 15-15;

[0044] FIG. 16 is pictorial representation of another screw pile end piece according to the invention;

[0045] FIG. 17 is an elevational view of the screw pile end piece of FIG. 16 from one side;

[0046] FIG. 18 is an elevational view of the screw pile end piece of FIG. 16 at 90 degrees to the elevational view of FIG. 17;

[0047] FIG. 19 is a top end view of the screw pile end piece of FIG. 16; and

[0048] FIG. 20 is a sectional elevational view of the screw pile end piece of FIG. 16 along lines 20-20 in FIG. 17.

DETAILED DESCRIPTION OF THE INVENTION

[0049] Referring to FIGS. 1-20, the screw pile stem 10 shown in FIG. 1 has a shank 11 with an inwardly tapered portion 12 at its lower end and a socket 13 at its upper end and a hollow cylindrical body portion 15 therebetween, the socket being adapted to receive therein the spigot 14 at the lower end of the extension stem 16 shown in-line for assembly, as will be described more fully later. A helical screw 18 formed of cast steel is welded to the shank with part of the helical screw being on the tapered portion and part of the cylindrical portion immediately adjacent to the tapered portion. Although the screw pile stem of this embodiment is circular in cross-section, it is to be understood that the term “cylindrical” used herein is to be understood as including elongate bodies of cross-sectional shapes other than circular and could, for example, be octagonal.

[0050] The part of the helical screw on the tapered portion extends approximately two and one-quarter turns and only one-quarter turn is on the cylindrical portion of the shank. However, in other embodiments, at least one full turn is on the cylindrical portion of the shank.

[0051] The socket 13 is defined by the upper end portion of the socket wall 22 which has been expanded to a suitable diameter to receive therein the spigot 14. Similarly the spigot 14 has been formed by expanding the lower end portion 24 of the hollow extension stem wall 17 to a suitable diameter which is an easy sliding fit in the socket 13, the spigot and socket being sized to transmit the desired torsional loads for installation and the desired bearing loads once installed.

[0052] Two opposite rows of three recesses 26 are formed in the socket wall 22, but not through the wall, each recess having an axially-extending recess portion 27 which opens to the upper end of the socket through the opening 28 and three axially spaced-apart circumferentially extending recess portions 29, 30 and 31 which are bisected by the axial portion 27 to form securing portions at each end 29a and 29b, 30a and 30b, and 31a and 31b, respectively.

[0053] Three sets of complementary axially-aligned protuberances 36, 37 and 38 are provided on the spigot and the recess is adapted to receive therein the protuberances through the opening 28, each protuberance being adapted to locate in a respective one of the securing portions of the recess upon relative partial rotation of the spigot and the socket to prevent relative axial movement therebetween. Thus, it can be seen that the extension stem can be fitted to the screw pile stem by aligning the protuberances with the opening 28 and sliding the spigot into the socket in an axial movement until the protuberances align with the securing portions of the recess whereupon the spigot can be partially rotated to locate the protuberances in the respective securing portions. It will be appreciated that in other embodiments the spigot and socket could be reversed so that the spigot is on the screw pile stem. Similarly, the recess could be provided on the spigot and the protuberances on the socket if desired. It will also be appreciated that in other embodiments there could be more or less circumferential recess portions, for example, four, and in that case an equal number of protuberances would be provided. Further, while this embodiment has the axial recess portion bisecting the circumferential recess portions, in other embodiments, the axial recess portion dissects it offset from the center.

[0054] The screw pile end piece 50 illustrated in FIG. 6 has a shank 51 with an inwardly tapered lower portion 52a which depends from a cylindrical upper portion 52b. The upper portion defines an upwardly open socket 63 adapted to receive therein the spigot 54 at the lower end of the pile stem 56 shown in FIG. 11. A helical screw 58 is integrally formed with the shank and about one full turn of the screw is on the cylindrical portion while about one and a half turns is on the tapered portion, the helical screw terminating a short distance from the tip 59 of the tapered portion. The major diameter of the helical screw on the cylindrical portion remains constant for the full turn. However, the major diameter of the helical screw on the tapered portion decreases constantly towards the tip at the same rate as the diameter of the tapered portion decreases. A notch 60 is formed in the tapered portion adjacent to the tip to provide a cutting edge 61 for initiating a drill hole for the pile.

[0055] As can be more clearly seen in FIG. 10, two opposed pairs of axially-aligned protuberances or lugs 62 and 63 extend radially into the socket for the cylindrical wall and are adapted to engage in a recess 66 provided in the wall of the spigot 54 of the pile stem 56 as will be described more fully later. It will be appreciated that the lugs cooperate with the recess in a similar manner to the protuberances and recesses described in relation to the screw pile stem of FIG. 1. Each recess 66 is pressed into the spigot wall thus maintaining the full wall thickness and the integrity of the spigot whereby it can transfer the torsional loads required to install the screw pile. Each recess 66 has an axially extending recess portion 67 which opens to the lower end of the spigot through opening 68 and two axially spaced apart circumferentially extending recess portions 69 and 70 which are bisected by the axial portion 67 to form opposed securing portions at their ends 69a and 69b, and 70a and 70b respectively.

[0056] It can be seen that at one end the extension stem 56 has the expanded spigot 54 and at the other end it has a complementary expanded socket portion 80 with the stem between the spigot portion and the socket portion being an unexpanded cylindrical tube 57. It can also be seen that the extension stem can be fitted to the screw pile end piece 50 in much the same manner as the extension stem 16 is fitted to the screw pile stem of FIG. 1; that is, by aligning the lugs or protuberances with the opening 68 and sliding the spigot into the socket in an axial movement until the protuberances align circumferentially with the circumferential portions of the recess whereupon the spigot can be partially rotated to locate the protuberances in the respective securing portions. It will be appreciated that for forward drive, the protuberances locate in securing portions 69b and 70b and upon reverse drive being commenced, the pile stem 56 rotates relative to the screw pile end piece 50 until the protuberances locate at the other end of the circumferential recess portions in securing portions 69a and 70a respectively and engage against the wall at the edge of the recess securing portions to cause reverse drive to be applied to the screw pile end piece 50.

[0057] As can be more clearly seen in FIG. 10, a shoulder 75 is provided at the inner end of the socket 53, the shoulder being adapted to abut the free end face 72 of the pile stem so that downward loads can be transmitted directly from the pile stem to the screw pile end piece via the shoulder. In order to ensure that the free end positively engages against the shoulder, the lowermost edges 69c and 70c of the securing portions of the recess 66 taper away from the free end face 72 whereby engagement of the protuberances 62 and 63 thereagainst urges the spigot 54 further into the socket 53.

[0058] The socket portion 80 of the pile stem 56 is similar to the cylindrical portion of the screw pile end piece 50 to the extent that it has opposed pairs of axially aligned lugs 82 and 83 therein which correspond with lugs 62 and 63 in shape and position and a shoulder 85 which corresponds to the shoulder 75 in the screw pile end piece. It will be understood that the socket portion is adapted to receive therein the spigot portion 54 of a like pile stem so that any number of pile stems can be added one after another to create a pile of any desired length adapted to be installed to any desired depth.

[0059] It is believed that a screw pile having a screw pile end piece of the type illustrated in FIG. 6 has the capacity to carry the desired structural load without unacceptable distortion while the arrangement of socket and spigot for coupling pile stems to each other and to the screw pile end piece has the capacity to transmit the torsional forces necessary to screw a pile with such an end piece to the desired depth. Additionally, the coupling arrangement allows removal of damaged stems from the screw pile end piece or from other stems by simply partially rotating the screw pile stems in reverse until the lugs align with the axial portion 67 of the recess 66 and then lifting the pile stem from the screw pile end piece or from the adjacent pile stem as the case requires.

[0060] The screw pile end piece 150 illustrated in FIG. 16 is intended to be permanently secured to the hollow pile stem, for example, by welding or pinning and includes a shank 151 having a tapered portion 152a at its lower end and a cylindrical portion 152b at its upper end, the cylindrical portion being adapted to engage in the hollow of the pile stem to which it is to be attached. A helical screw 158 is integrally formed with the shank, the whole of the helical screw being on the tapered portion. The first turn of the helical screw (that is, the uppermost turn) has a constant major diameter but its minor diameter, being the outer diameter of the tapered portion of the shank, decreases constantly over the turn. The major diameter and the minor diameter of subsequent turns decrease constantly towards the tip 159 of the tapered portion.

[0061] While the foregoing description has been given by way of illustrative example of the invention, it will be understood that the invention may be embodied in many other forms and all such forms are deemed to fall within the broad scope and ambit of the invention as defined by the appended claims.