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Title:
GROUND ANCHOR
Document Type and Number:
WIPO Patent Application WO/2007/033413
Kind Code:
A1
Abstract:
A ground anchor (10) comprising an anchor shaft (11) and an anchoring screw (13) moulded onto the anchoring shaft adjacent the lower end thereof. The anchoring shaft (11) is of a rectangular cross-section with four side walls (12). The anchoring shaft (11) is configured at its bottom end (15) for ground penetration. The upper end (19) of the anchor shaft (11) is configured to receive torque applied thereto. The anchoring screw (13) comprises a hub (21) and a screw flight (23) on the hub. The anchoring screw (13) is moulded onto the anchor shaft (11), and the hub (21) is keyed to the anchor shaft. The anchoring screw (13) is so constructed that the spiral flight (23) is rigid yet has some resilient flexibility which allows the flight to deflect laterally in the direction of the screw axis. Specifically, the screw flight (23) has sufficient rigidity to allow it to penetrate the ground in which it is intended to be used when torque is applied to the anchor shaft (11). Further, the screw flight (23) has sufficient rigidity in order to retain the ground anchor (10) embedded in the ground when subjected to the normal load conditions for which it is intended, as is the case with conventional ground anchors. The resilient flexibility provides the screw flight (23) with a degree of "springiness", so allowing the screw flight (23) to deflect laterally in the direction of the screw axis when subjected to the loadings to which it is exposed when winding into the ground. With this arrangement, the pitch of the helical screw (25) is permitted to alter during ground embedment as ground pressure increases.

Inventors:
LEWENHOFF, Stephen, Mark (80 Lockwood Street, Yokine, Western Australia 6060, AU)
Application Number:
AU2006/001374
Publication Date:
March 29, 2007
Filing Date:
September 20, 2006
Export Citation:
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Assignee:
LEWENHOFF, Stephen, Mark (80 Lockwood Street, Yokine, Western Australia 6060, AU)
International Classes:
E02D5/80; E04H15/62
Domestic Patent References:
WO1999014441A11999-03-25
WO1988008266A11988-11-03
Foreign References:
GB2305948A1997-04-23
Other References:
DATABASE WPI Week 198351, Derwent World Patents Index; Class Q42, AN 1983-849385, XP003010592
DATABASE WPI Week 198427, Derwent World Patents Index; Class Q42, AN 1984-169578, XP003010593
Attorney, Agent or Firm:
WRAY & ASSOCIATES (Level 4, The Quadrant 1 William Stree, Perth Western Australia 6000, AU)
Download PDF:
Claims:

The Claims Defining the Invention are as Follows:

1. A ground anchor comprising an anchoring screw, the anchoring screw comprising a screw flight winding about a screw axis, the screw flight being generally rigid with some lateral resilient flexibility.

2. A ground anchor according to claim 1 wherein the screw flight is formed from a moulded non-metallic material.

3. A ground anchor according to claim 2 wherein the screw flight is formed of a composite plastics material.

4. A ground anchor according to claim 1 , 2 or 3 wherein the screw flight is supported on a hub.

5. A ground anchor according to claim 4 wherein the screw flight is formed integrally with the hub.

6. A ground anchor according to claim 5 wherein the anchoring screw is moulded from a composite plastics material.

7. A ground anchor according to any one of the preceding claims further comprising an anchor shaft on to which the anchoring screw is mounted.

8. A ground anchor according to claim 7 wherein the anchoring screw is moulded onto the anchoring shaft.

9. A ground anchor according to claim 8 wherein the anchoring shaft is configured for keying the moulded anchoring screw onto the shaft.

10. A ground anchor according to claim 7, 8 or 9 wherein the anchoring shaft is of a polygonal cross-section, such as hexagonal or rectangular cross- section.

11. A ground anchor according to any one of claims 7 to 10 wherein the anchor shaft has a foot end configured for ground penetration.

12. A ground anchor according to any one of claims 7 to 11 wherein the anchor shaft has a head end adapted to receive torque to drive the anchor into the ground.

13. A ground anchor according to claim 12 wherein the head end of the anchor shaft incorporates at least one drive hole located through the side of the shaft.

14. A ground anchor according to any one of the preceding claims wherein the screw flight is adapted for selective variation of the circumference thereof.

15. A ground anchor according to claim 14 wherein the screw flight is adapted to be cut to vary the circumference thereof,

16. A ground anchor according to claim 15 wherein the screw flight incorporates a guide marking radially inwardly of the outer periphery thereof.

17. A ground anchor comprising an anchor shaft and an anchoring screw on the anchor shaft, the anchoring screw comprising a screw flight winding about a screw axis, the screw flight being generally rigid with some lateral resilient flexibility.

18. A ground anchor according to any one of claims 7 to 17 further comprising a lateral stabilisation device adapted to be fitted onto the anchor shaft and to engage the ground to provide lateral stabilisation to the shaft within the ground.

19. A ground anchor according to claim 18 wherein the lateral stabilisation device comprises a body adapted to be fitted onto the anchor shaft for engagement with the ground to provide lateral support for the anchor shaft with respect to the ground.

20. A ground anchor according to claim 19 wherein the body is adapted to be rotatably supported on the shaft.

21. A ground anchor according to claim 20 wherein the body incorporates a bearing surface and the anchor shaft is provided with an abutment for engaging against the bearing surface for urging the body into engagement with the ground as the ground anchor is embedded into the ground.

22. A ground anchor according to claim 21 wherein the bearing surface is defined by a thrust bearing in the body.

23. A ground anchor according to claim 21 or 22 wherein the abutment provided on the anchor shaft comprises a pin projecting from the shaft.

24. A ground anchor according to any one of claims 19 to 23 wherein the body comprises one or more lateral projections presenting surfaces for engagement with the ground.

25. A ground anchor according to claim 24 wherein the lateral projections are configured as vanes.

26. A ground anchor according to claim 25 wherein there are four vanes arranged in an X formation when viewed in plan.

27. A ground anchor according to claim 25 or 26 wherein each vane is configured at the lower end thereof for penetration with the ground.

28. A ground anchor according to any one of claims 19 to 27 wherein the body further comprises a sleeve section defining a central passage for rotatably receiving the anchoring shaft.

29. A ground anchor according to any one of claims 19 to 28 wherein the body comprises a plurality of body sections.

30. A ground anchor according to any one of claims 19 to 29 wherein the body incorporates a recess for accommodating the upper end of the anchor shaft, the recess being configured to facilitate access to the upper end of the anchor shaft when accommodated in the recess.

31. A method of manufacturing a ground anchor, the method comprising providing an anchor shaft and moulding an anchoring screw onto the anchor shaft.

32. A method according to claim 31 further comprising configuring the shaft for keying the moulded anchoring screw onto the anchor shaft.

33. A lateral stabilisation device for a ground anchor having an anchor shaft, the lateral stabilisation device comprising a body adapted to be fitted onto the anchor shaft for engagement with the ground to provide lateral support for the anchor shaft with respect to the ground.

34. A lateral stabilisation device according to claim 33 wherein the body is adapted to be rotatably supported on the anchor shaft.

35. A lateral stabilisation device according to claim 34 wherein the body incorporates a bearing surface against which an abutment on the anchor shaft can engage for urging the body into engagement with the ground as the ground anchor is embedded into the ground.

36. A lateral stabilisation device according to claim 35 wherein the bearing surface is defined by a thrust bearing in the body.

37. A lateral stabilisation device according to any one of claims 33 to 36 wherein the body comprises on© or more lateral projections presenting surfaces for engagement with the ground.

38. A lateral stabilisation device according to claim 37 wherein the lateral projections are configured as vanes.

39. A lateral stabilisation device according to claim 38 wherein there are four vanes arranged in an X formation when viewed in plan.

40, A lateral stabilisation device according to claim 38 or 3θ wherein each vane is configured at the lower end thereof for penetration with the ground.

41. A lateral stabilisation device according to any one of claims 33 to 40 wherein the body further comprises a sleeve section defining a central passage for rotatably receiving the anchoring shaft.

42, A lateral stabilisation device according to any one of claim 33 to 41 wherein the body comprises a plurality of body sections.

43. A lateral stabilisation device according to any one of claims 33 to 42 wherein the body incorporates a recess for accommodating the upper end of the anchor shaft, the recess being configured to facilitate access to the upper end of the anchor shaft when accommodated in the recess.

44. A ground anchor substantially as herein described with reference to the accompanying drawings.

45. A method of manufacturing a ground anchor substantially as herein described.

46. A lateral stabilisation device substantially as herein described with reference to the accompanying drawings.

Description:

"Ground Anchor"

Field of the Invention

The present invention relates to ground anchors, and more particularly to ground anchors employing an anchoring screw to embed the anchor into the ground. Ground anchors are also often referred to as earth anchors.

Background

Anchors installed in soil are commonly utilised to provide support, either in tension or in compression, and provide support or a tie down point for various equipment and structures. For example, ground anchors are commonly utilised to provide anchorage, in tension, for guy lines used to support electrical transmission equipment. They can also be used to provide a stable surface upon which equipment can be mounted. When this is done, the top of the anchor is normally encased in concrete to provide fateral (ie side to side) stability and the equipment is mounted thereupon.

Ground anchors typically include a helix formed in a spiral configuration around a hub. The helix is rigid and most commonly of metal. Some designs have used a cast iron type helix whereas other designs have the metal helix welded to a metal hub. When the ground anchor is to be installed into the ground, a torque tube is coupled to the hub of the anchor so that the torque applied to the torque tube is transferred through the hub from the torque tube to the helix. The torque tube is controlled to then apply both a downward force and a rotational force to the ground anchor. The combination of forces (at least initially) causes the helix to bore into the ground.

Since it is primarily the helix of the ground anchor that absorbs the load exerted on the earth, the strength and diameter of the helix must be designed to withstand its expected load. Typically different sized anchors are provided for dffferent intended purposes (taking into account expected loads and ground conditions).

There have been various prior art proposals for ground anchors. US 3,1487,510 (Sullivan) discloses a method of driving a screw anchor into the ground. The anchor itself is of a conventional design and uses a rigid shaft and a rigid helical screw. The method of inserting the anchor is depicted by way of specialised industrial equipment. US 4,316,350 (Watson) discloses a ground having a helical screw with an increasing radial extent from the tip of the screw towards the top of the anchor. US Re 32,076 (US 4,334,392 - Dziedzic) discloses a helical screw type anchor for industrial applications wherein the anchor comprises individual components adapted to be assembled together. Specialised equipment is used to install such anchors. US 5,156,369 (Tizzoni) discloses a helical screw applied to the lower part of an beach umbrella stand. The umbrella stand is adapted at its upper part to receive a tool for rotating the stand and thereby embedding the helical screw into the ground. US 5,265,982 (Burtelson) discloses a ground anchor in which the hub carrying the helical screw is adapted to engage a torque tube for transferring torque from the torque tube to the helix. The design is said to allow a greater torque to be applied to the helical screw for a lower manufactured cost, and the helix is typically attached to the hub by welding.

The anchors described in the prior art all teach of the use of rigid helical screws and all are of rnotaL

The torque required to install a helical screw ground anchor into a given ground condition will be dependent on the size of the helical screw. A low torque is particularly desirable for helical screw ground anchors intended for manual operation and therefore smaller (rather than larger) helical screws are desirable.

Reducing the friction between the helical screw and the earth would also reduce the torque required for installation or removal.

Further in all of the above prior art cases, the width of the anchor shaft is relatively narrow as compared to the diameter of the helical screw. Therefore the ability of the ground anchor to resist lateral loads (ie transverse to the longitudinal direction of the anchor shaft) is limited in comparison to the ground holding ability of the helical screw.

In order to provide lateral stability to the top of such ground anchors, concrete can be poured in-situ to encapsulate the top of the anchor and provide a mounting point for equipment or other hardware.

Such in-situ stabilisation is time consuming and labour and material intensive.

It is against background, and the problems and difficulties associated therewith, that the present invention has been developed.

Disclosure of the Invention

According to a first aspect of the invention there is provided a ground anchor comprising an anchoring screw, the anchoring screw comprising a screw flight winding about a screw axis, the screw flight being generally rigid with some lateral resilient flexibility.

With this arrangement, the rigid nature of the screw flight allows it to move through the ground during rotation while also allowing some lateral deflection in response to loading on the screw flight to change the pitch of the flight.

Such an arrangement offers an increased loading capacity compared to prior art designs of a similar size.

The degree of resilient flexibility desirable for a particular ground anchor according to the invention may be dependent, amongst other things, on the nature of the ground into which it will be inserted (eg sandy loose soil would require a more flexible helical screw than say, hard compacted soil). Simple application engineering techniques, either mathematical model based or routine trial and experimentation, would identify suitable flexibility requirements for any particular application.

Preferably, the screw flight is formed from a moulded non-metallic material, such as a semi-rigid composite material or other plastics material. More preferably, the

- A - entire anchoring screw formed on such material. Such materials are inherently more flexible then the metal helical screws typically used in the prior art.

The anchoring screw may be made of a composite plastics material. The desired flexibility of the screw flight can be conveniently controlled by suitable choice of materials, and/or the thickness of the screw flight.

Use of such materials also reduces the friction between the screw flight and the earth, and thus can provide benefits in reducing the insertion torque.

Preferably the non-metallic material is corrosion resistant. , As such the torque required to remove an anchor that has been in the ground for a period of time is reduced. Such ground anchors are therefore well suited for re-usable applications.

Preferably the screw flight is formed of a material that can be cut (such as by sawing) for selectively varying the circumference thereof. Further, the screw flight may have a circumferential guide marking radially inwardly of the outer periphery of the helical screw, such guide marking providing a visual guide for cutting off an outer section of the screw flight. Preferably the screw flight can be so cut manually.

With such an arrangement, a user of such ground anchor, upon determining that a smaller diameter screw flight is desirable for a particular application (for instance, where the ground is hard/compacted and therefore the insertion torques would be exceedingly high for a large diameter screw flight) can conveniently reduce the radial extent of the screw flight, thus reducing the torque and loads required to embed the ground anchor.

Preferably, the screw flight is configured as a helical screw.

Preferably, the screw flight is supported on a hub.

Preferably, the screw flight is formed integrally with the hub.

Preferably, the ground anchor further comprises an anchor shaft on to which the anchoring screw is mounted.

The anchor shaft may be of hollow construction or solid construction.

The tensile strength of the anchor shaft may be such that sufficient torsional capacity is available to effectively wind the anchor into the ground. Thus a separate torque tube need not be necessary.

The anchor shaft may be of one-piece construction or alternatively it may comprise a plurality of sections adapted to be fitted together. The latter arrangement is advantageous in that it provides for selective variation of the length of the anchor shaft.

Preferably, the anchoring screw is secured in position on the anchoring shaft. Conveniently, the anchoring screw may be moulded onto the anchoring shaft The anchoring shaft may have provision for keying the moulded anchoring screw onto the shaft.

Conveniently, the anchoring shaft is of a cross-sectional shape other than circular in order to facilitate torque transmission between the anchoring shaft and the anchoring screw without relying totally on the bond therebetween. Conveniently, the anchoring shaft is of a polygonal cross-section, such as hexagonal or rectangular cross-section.

Without wishing to be limited as to the technical correctness of such beliefs, the inventor believes that reasons as to why the use of a resilientty flexible screw flight provides an improvement in the ground holding ability of a ground anchor, resides in the fact that the pitch of the helical shape is permitted to alter during ground embedment as ground pressure increases. It is believed that the change in pitch effectively compresses the soil in a given zone. Such compression effectively extends the zone of influence of the helical screw beyond the diameter of the helical screw itself. Thus the effective diameter of the screw flight is increased. Put another way, the action of the resilieπtly deformed helical shape

creates increased soil pressure providing additional breakout threshold capacity in shallow anchoring applications, thus improving the effectiveness of the anchor for a given helix size.

Furthermore, it has been found that flexibility provided by the flexible helical shape material behaves as a shock absorber in cyclic tensile load conditions, reducing the snatch effect upon connections to the ground anchor (such as connecting tendons or guy wires).

The transfer of the downward and rotational forces to the screw flight via the anchor shaft, and the subsequent transfer of those forces into the ground effects anchor embedment. These forces allow simultaneous embedment of the helical shape and the anchor shaft. The configuration of the screw flight pulls the complete assembly into the ground to the required depth.

Preferably, the anchor shaft has a foot end configured for ground penetration. The end may also be configured to displace the soil around the shaft.

Preferably, the head end of the anchor shaft ϊs tilised to drive the anchor into the ground. Typically the head end is square or hexagonal to accept drive adaptors.

The head end of the anchor shaft may have at least one drive hole located through the side of the shaft. The drive hole may accept a drive pin.

The invention lends itself particularly well to ground anchors that can be manually inserted, or inserted with the use of conventional and readily available tools, such as wrenches, spanners or hand operated power tools (eg battery operated drills). The ground anchor may, for example, be wound into the ground manually using a tool such as a T-bar arrangement.

The ground anchor may be removable by reversing the direction of embedment rotation force. The opposite rotation force required to withdraw the ground anchor is typically less than the original installation force due to the behaviour of the flexible screw. Specifically, tension induced in the screw flight as it resiliently

deflects during installation of the ground anchor is of assistance in the unwinding action.

Preferably, the ground anchor is intended for reusable use.

According to a second aspect of the invention there is provided a ground anchor comprising an anchor shaft and an anchoring screw on the anchor shaft, the anchoring screw comprising a screw flight winding about a screw axis, the screw flight being generally rigid with some lateral resilient flexibility.

The ground anchor according to the invention may be used in conjunction with a lateral stabilisation device adapted to be fitted onto the anchor shaft and to engage the ground to provide lateral stabilisation to the shaft within the ground.

Preferably the lateral stabilisation device comprises a body adapted to be fitted onto the anchor shaft for engagement with the ground to provide lateral support for the anchor shaft with respect to the ground.

Preferably, the body is adapted to be rotatably supported on the shaft. In this way, the body can be drawn into engagement with the ground surface as the ground anchor is embedded into the ground. Because the body is rotatably supported with respect to the anchor shaft, the anchor shaft can rotate as the anchor is embedded into the ground while the body does not rotate.

Preferably, the body incorporates a bearing surface and the shaft is provided with an abutment for engaging against the bearing surface for urging the body into engagement with the ground as the ground anchor is embedded into the ground. The bearing surface may be defined by a thrust bearing in the body. Typically, the thrust bearing is of metal. The abutment provided on the anchor shaft may comprise a pin projecting from the shaft

The body may comprise one or more lateral projections presenting surfaces for engagement with the ground.

Preferably there are a plurality of the lateral projections. The lateral projections may be configured as vanes. Conveniently there are four vanes arranged in an X formation when viewed in plan.

Each vane may be configured at the lower end thereof for penetration with the ground.

Preferably, the body further comprises a sleeve section defining a central passage for rotatably receiving the anchoring shaft.

Preferably, the sleeve and the vanes are formed of a plastics material.

The body may be of one-piece construction or it may be assembled from a plurality of body sections. The latter arrangement is particular convenient as it allows the length of the stabilisation device to be selected according to the requirements of the installation site.

Where the body is formed of a plurality of sections, the sections preferably comprise a lowermost section and an uppermost section. There may also be one or more intermediate sections adapted for location between the lowermost and uppermost sections.

Preferably, the lowermost section is configured for penetrating the ground.

Preferably, the uppermost section preferably incorporates the bearing surface.

The uppermost section may be adapted to receive a fitting to which an object to be anchored by the ground anchor can be attached ' The fitting may comprise a plate adapted to be releasably attached to an upper surface of the upper most body section. Thθ plate may carry a coupling element.

According to a third aspect of the invention there is provided a method of manufacturing a ground anchor, the method comprising providing an anchor shaft, and moulding an anchoring screw onto the anchor shaft.

Preferably, the method further comprises configuring the shaft for keying the moulded anchoring screw onto the shaft.

According to a fourth aspect of the invention there is provided a lateral stabilisation device for a ground anchor having an anchor shaft, the lateral stabilisation device comprising a body adapted to be fitted onto the anchor shaft for engagement with the ground to provide lateral support for the anchor shaft with respect to the ground. Preferably, the body is adapted to be rotatably supported on the shaft.

Preferably, the body incorporates a bearing surface against which an abutment on the anchor shaft engages for urging the* body into engagement with the ground as the ground anchor is embedded into the ground.

The body may be configured to present one or more lateral surfaces for engagement with the ground.

Brief Description of the Drawings

The invention will be better understood by reference to the foilowing description of several specific embodiments thereof as shown in the accompanying drawings in which:

Figure 1 is a schematic perspective view of a ground anchor according to a first embodiment;

Figure 2 is a side elevational view of the ground anchor of the first embodiment;

Figure 3 is a fragmentary perspective view of the lower end of the ground anchor showing in particular the anchoring screw;

Figure 4 is a view similar to Figure 3 but viewed from a different position;

Figure 5 is a side elevational view of the anchoring screw;

Figure 6 is a plan view of the anchoring screw;

Figure 7 is a side view of a ground anchor according to a second embodiment;

Figure 8 is a plan view of an anchoring screw for a ground anchor according to a third embodiment;

Figure 9 is a plan view of an anchoring screw for a ground anchor according to as fourth embodiment;

Figure 10 is a plan view of an anchoring screw according to a fifth embodiment;

Figure 11 is a fragmentary side elevational view of a ground anchor according to a sixth embodiment, with the ground anchor incorporating a lateral stabilisation device;

Figure 12 is a view similar to Figure 11 with the exception that the lateral stabilisation device is shown in section;

Figure 13 is a perspective view of the ground anchor shown in Figure 11 , but with the lateral stabilisation device shown in an exploded condition;

Figure 14 is an exploded perspective view of the lateral stabilisation device;

Figure 15 is a side elevational view of a ground anchor according to a seventh embodiment for supporting a pole;

Figure 16 is a fragmentary view of the ground anchor of Figure 15, with the ground anchor being shown supporting a pole in a tilted condition; and

Figure 17 is a fragmentary view of the ground anchor of Figure 15 shown in a condition for installation.

Best Mode(s) for Carrying Out the Invention

Referring to Figures 1 to 6, there is shown a ground anchor 10 according to a first embodiment. The ground anchor 10 comprises an anchor shaft 11 and an anchoring screw 13 fitted onto the anchoring shaft adjacent the lower end thereof. The anchoring shaft 11 is of polygonal cross-sectional, and in the arrangement shown is of rectangular cross-section with four side walls 12. The anchoring shaft

11 is configured at its bottom end 15 for ground penetration. In the arrangement shown, the bottom end is provided with a point 17 generated by an angular cut on the shaft. The point 17 serves to penetrate the ground and also displace soil sidewardly as it advances through the ground.

The upper end 19 of the anchor shaft 11 is configured to receive torque applied thereto. The upper end 19 may be configured to receive a tool such as a torque tube through which torque may be applied to the anchor shaft 11. The torque may be applied manually or through a power device, such as for example, a portable eiectric drill.

The upper end 19 also incorporates at least one transverse hole 20 which can receive a drive pin or provide an attachment point.

The anchoring screw 13 comprises a hub 21 and a screw flight 23 on the hub. In this embodiment, the screw flight 23 is formed integrally with the hub 21. The screw flight 23 comprises a helical screw 25 having a leading end 27 and a trailing end 29 extending outwardly of the hub 21. The screw flight 23 presents a spiralling upper surface 31 and a spiralling lower surface 32. The upper and lower surfaces 31 , 32 taper inwardly with respect to each other in the radially outer direction and terminate at a peripheral edge 33.

The screw flight 23 winds about a screw axis through approximately one revolution such that the trailing edge 29 is located approximately above the leading edge 27 at a spacing corresponding to the pitch of the spiral flight. The screw axis is coincident with the central longitudinal axis of the anchor shaft 11.

The anchoring screw 13 is moulded onto the anchor shaft 11 , and the hub 21 is keyed to the anchor shaft. This is achieved by the provision of keys (not shown) configured as transverse channels in at least some of the side walls 12 of the anchor shaft. Further, one or more of the side walls 12 may be deformed in order to promote keying with the hub 21. With this arrangement, the anchoring screw 13 is keyed to the anchor shaft 11 when it is moulded into position onto the anchor shaft.

The anchoring screw 13 is formed of a composite plastics material, having a high stiffness, such as Nylon 66 incorporating reinforcing fibres.

The anchoring screw 13 is so constructed that the spiral flight 23 is rigid yet has some resilient flexibility which allows the flight to deflect laterally in the direction of the screw axis. Specifically, the screw flight 23 has sufficient rigidity to allow it to penetrate the ground in which it is intended to be used when torque is applied to the anchor shaft 11. Further, the screw flight 23 has sufficient rigidity in order to retain the ground anchor 10 embedded in the ground when subjected to the normal load conditions for which it is intended, as is the case, with conventional ground anchors.

The resilient flexibility provides the screw flight 23 with a degree of "springiness", so allowing the screw flight to deflect laterally in the direction of the screw axis when subjected to the loadings to which it is exposed when winding into the ground. With this arrangement, the pitch of the helical screw is permitted to alter during ground embedment as ground pressure increases. It is believed that the change in pitch effectively compresses the soil in a given zone. Such compression effectively extends the zone of influence of the anchoring screw 13 beyond the diameter of the anchoring screw itself. Thus the effective diameter of the anchoring screw is increased. Furthermore, the resilient flexibility of the screw flight 23 can function to absorb shock in cyclic tensile toad conditions, thereby reducing the snatch effect upon connections to the ground anchor.

The extent of resilient deflection of the screw flight 23 can depend upon various factors, including the density of the soil, the size and configuration of the helical

screw 25, the size of the anchor shaft 11 , and the size of the helical screw 25 in proportion to the size of the anchor shaft 11.

The pitch change can be in the order of about 1mm or less in certain cases. In other cases, it may be up to 20mm or more.

The screw flight 23 is adapted for selective variation of the circumference thereof. In this embodiment, markings 40 are provided on one side of the spirally flight 29, typically the underside 32. The markings 40 may comprise guide lines 41 along which the spiral flight 23 can be cut in order to reduce the outer diameter of the spiral flight 23 if desired. In the arrangement shown, there are two guide lines 41 , so offering two alternative sizes for the helix. Typically, the spiral flight 23 would be cut along the inner mark for dense soil conditions and along the outer mark for firm soil conditions. The spiral flight would be retained at its original size for loose soil conditions.

The ground anchor 10 is wound into the ground in the conventional way; that is, by application of embedment torque to the upper end 19 thereof. The torque can be applied in any appropriate way, such as manually using a tool such as a T-bar arrangement or using a power assisted means such as an electric or battery operated hand drill coupled to the anchoring shaft through a connecting socket.

The ground anchor 10 is removable by reversing the direction of the embedment torque. The reverse torque required to withdraw the ground anchor is likely to be less (and possibly considerably less) than the original installation force due to the behaviour of the resiliency flexible spiral flight 23.

Referring now to Figure 7 of the drawings, there is shown a ground anchor 50 according to a second embodiment. The ground anchor 50 according to the second embodiment is similar in many respects to the ground anchor 10 according to the first embodiment and so corresponding reference numerals are used to identify corresponding parts. In this second embodiment, the ground anchor 50 is provided with a second anchoring screw 51. The second anchoring screw 51 is of a similar construction to the first anchoring screw 13 and is spaced

therefnom along the anchoring shaft 11. More anchoring screws may also be provided on the anchoring shaft for certain applications, if desired.

In the first and second embodiments, the leading and trailing edges 27, 29 of the screw flight 23 extend outwardly from the hub 21 in a generally radially direction. Other arrangements are, of course, possible. Several possible variations are illustrated in Figures 8, 9 and 10 of the drawings. As each anchoring screw is of a somewhat similar configuration to the anchoring screw 13 of the first embodiment, corresponding reference numerals will be used to identified corresponding parts.

Referring now to Figure 8, there is shown an anchoring screw 60 for a ground anchor according to a third embodiment. In this embodiment, the leading edge 27 of the spiral flight 23 is not generally straight (as was the case with the previous embodiments) but rather it is configured to present a curved profile 61 towards the radially outer end thereof. The curved profile 61 comprises a curve which merges wfth the outer circumference 33. The curved configuration serves to displace rock and debris in the path of the leading edge 27 outwardly away from the rotating helix as it winds into the ground.

With the arrangement shown in Figure 8, the curved profile 61 can increase the horizontal component of separation between the leading and trailing edges of the screw. In certain circumstances, such separation may be undesirable as it may disrupt the uniformity of loading on the anchoring screw. With a view to addressing this deficiency, the anchoring screw may be configured so that there is some vertical overlap between the leading and trailing edges. Such an arrangement is provided by the next embodiment. Referring now to Figure 9, there is shown an anchoring screw 70 for a ground anchor according to a fourth embodiment. In this embodiment, the leading edge 27 incorporates the rounded profile 61 of the previous embodiment but the relative positions of the leading and trailing edges are moved angularly such that there is overlap therebetween.

There may be some situations where there is no need to provide overlap between the leading and trailing edges 27, 29 of the this anchoring screw. Such an arrangement is provided by the next embodiment. Referring now to Figure 10 of

the drawings, there is shown an anchoring screw 80 for such a ground anchor according to a fifth embodiment. As can be seen in Figure 10, the spacing between the leading and training edges 27, 29 has a horizontal component.

With regard to the arrangements shown in Figures S, 9 and 10, it should be understood that the profile of the rounded leading edge can vary.

In certain applications, it may be desirable or necessary to provide the anchoring shaft with lateral stability when embedded in the ground. Referring now to Figures 11 to 14, there is. shown a ground anchor 100 having provision for lateral support at the upper end thereof.

The ground anchor 100 according to this embodiment is similar to the ground anchor 10 according to the first embodiment, and so corresponding reference numerals are used to identify corresponding parts. In this embodiment, the provision for lateral support comprises a device 110 adapted for location on the anchor shaft 13. The device 110 comprises a body 111 adapted to be fitted onto the upper end portion of the anchor shaft 11. The body 111 comprises a central sleeve 113 which is of cylindrical configuration and which defines a central passage 115 into which the anchor shaft 11 can be received. The central passage 115 is so dimensioned that the anchor shaft can rotate within the passage. The central passage 115 has an enlarged section 117 adjacent its. upper end. Thθ enlarged section 117 opens onto the top end 119 of the body defined by a top wall 120. A shoulder 121 is defined at the inner end of the enlarged section 117.

The shoulder 121 provides a seat 123 for a thrust bearing 125. In this embodiment, the thrust bearing 125 comprises a washer which is located on the seat 123. The thrust bearing 125 is adapted to present a rigid surface against which an abutment 127 on the anchor shaft 13 can bear to transmit an axial force from the anchor shaft 11 to the body 111. In this embodiment, the abutment 127 comprises a drive pin 129 accommodated in the transverse hole 20 in the shaft.

The enlarged section 117 defines a recess 131 in which the drive pin 129 and the end portion of the anchor shaft 13 thereabove can be accommodated. A cap 133 is provided for closing the upper end of the recess 131. The cap 133 may be of tamper-proof construction. The cap 133 presents an outer surface 135 which locates within the plane of the surface 137 at the top end 119 of the body.

The body 111 is provided with a plurality of vanes 141 projecting radially outwardly from the central sleeve portion 113. Each vane 141 presents two opposed broad side surfaces 143, 144 and an outer edge 145. In the arrangement shown, there are four vanes 141 , arranged in an X configuration when viewed in plan.

The vanes 141 are formed integrally at their upper end 151 with the top wall 120 of the body. Further, the vanes 141 are configured at their lower ends 153 to penetrate the ground. In this regard, the lower ends 153 are provided with angled corners 155 which provide a somewhat pointed configuration to the lower end. of the body 111 for ground penetration.

While the body 111 can be of one piece construction, it comprises a plurality of sections 160 in this embodiment. The sections 160 comprise a lowermost section 161 , an uppermost section 162 and an intermediate section 163 between the lowermost and uppermost sections. The lowermost section 161 is configured to incorporate the angled corners 155. The uppermost section 162 is configured to incorporate the recess 131. With this arrangement, each vane 141 also comprises three vane sections.

The three body sections 161, 162 and 163 are adapted to be connected one with respect to another to restrain relative rotation therebetween. The connection is by way of locating spigots 171 provided on one body section for location in matching sockets 173 provided on an adjacent body section. Specifically, the bottom edge of each vane section of the upper body section 163 is provided with a spigot 173 for location in a corresponding socket 173 on the upper edge of the adjacent intermediate vane section. Further, the lower edge of the intermediate vane

section is provided with a spigot 171 for location in a corresponding socket 173 on the upper edge of the adjacent lower vane section.

The top wall 120 of the body 111 is adapted to support a plate (not shown) which can be secured thereto by a fasteners such as screws threadedly engaging holes 185 incoφorated in the vanes 141. The vanes 141 incorporate boss sections 185 at their upper, ends to accommodate the holes. The plate supports at coupling

185 which a device to be anchored with respect to the ground by way of the ground anchor 100 can be tethered. The coupling may comprise a coupling pin upstanding from the plate and secured to in a manner permitting axial rotation of the pin with respect to the plate. The coupling may further comprise a shackle connected to the pin.

In this embodiment, the body 111 is moulded from a plastics material.

In operation, the device 110 is embedded into the ground by the driving and pulling forces exerted on it by the ground anchor 100 as the latter is embedded in the ground. The recess 131 at the upper end of the body 111 provides access to the upper end 19 of the anchor shaft 13 for application of embedment torque to the ground anchor. More particularly, the recess provides access for a torque tube to be fitted onto the upper end of the ground anchor 100. Further, the recess 131 provides access for anchoring onto the anchor shaft 11 , if required.

As the ground anchor 100 is installed into the ground, the drive pin 129 engages against the thrust bearing 125 and applies a downward force onto the body 111, so urging the body into contact with the ground. Once the body 111 contacts the ground it is restrained against rotation because of the engagement with the ground. However, this does not interfere with continued rotation of the anchor shaft 11 which can freely rotate within the central sleeve portion 113 of the body 111 and the thrust bearing 125 as previously explained. The drive pin 129 rotates with the anchor shaft 13 and is in sliding contact with the thrust bearing 125. The continued downward movement of the anchor shaft 13 applies an ongoing downward force to the body 111 through engagement between the drive pin 129. The leading (lower) end of the body 111 engages and cuts the ground during

downward movement of the body. At completion of the installation process, both the ground anchor 100 and the device 110 are locked into the ground. Typically, installation is complete when the upper end of the device 110 is at ground level.

Once the device 100 is in the ground, it provides lateral support for the anchor shaft 13. The lateral support is afforded by the presence of the vanes 141 which project outwardly and present broad opposed surfaces to the ground. With this arrangement, the device 110 can transfer any horizontal load exerted on the anchor to the surrounding ground and in this way utilise the passive resistance properties of the ground to transfer these loads. This action limits the sideways movement of the ground anchor when subjected to such horizontal loads.

The body 111 is locked into the ground by the drive pin 129 pushing down on the bearing 125 and the passive resistance of the soil against the body 11 i (including against top wall 120), as well as the increased resistance of the soil pressure against the ground anchor helical shape as it changes in helical plane pitch.

The length of the body 111 is selected according to the load to be anchored and the characteristics of the installation site. The length can be varied as necessary by incorporating one or more of the intermediate body sections 163, or alternatively omitting the intermediate body section 163 when a short length be required. Indeed, in certain applications, it may be appropriate to use only the uppermost section 162.

The device 110 is automatically installed in the ground at the same installation angle as the ground anchor.

Referring now to Figures 15, 16 and 17, there is shown an anchoring arrangement 180 designed particularly to support an upstanding elongate element such as a pole 181. The pole 181 may comprise, for example, the shaft of a beach umbrella.

The anchoring arrangement 180 comprises a ground anchor 185 of similar construction to the ground anchor 10 according to the first embodiment and a

coupling 187 at the upper end of the ground anchor for receiving and supporting the pole 181.

The coupling 187 comprises a sleeve 189 for receiving and supporting the lower end of the pole and locking means 191 for releaseably locking the pole 181 within the sleeve. In the arrangement shown, the locking means 191 comprises a hand screw 193 operable to bear at its inner end against the pole 181 and thereby clampingly retain it within the sleeve 189. The sleeve 189 is connected to the anchor shaft 13 by way of hinge mechanism 195 incorporating hinge pin 197. With this arrangement, sleeve 189 can be rotated through 90 degrees, between an upright condition (as shown in Figure 15) to support the pole in an upright position, and a generally horizontal condition in which the sleeve 189 can function as a handle for turning the anchoring shaft 11 for manual installation of the ground anchor 10 (as shown in Figure 16).

A releasable locking mechanism 199 for locking the sleeve 189 in the upright condition. The locking mechanism 199 also has provision for locking the sleeve 189 in a selected one or more of available angular conditions between the upright condition and the horizontal condition, one such angular conditions being the angular position shown in Figure 17. The locking mechanism 199 may also lock the sleeve 189 in the horizontal condition.

From the foregoing, it is evident that the present embodiment provides a simple yet highly effective ground anchor which has improved performance characteristics arising from the substantially rigid yet resiliently flexible characteristics of the spiral flight.

The ground anchor according to the invention can be used in a wide range of applications, as would be apparent to a skilled addressee. The ground anchor is, however, particularly suitable for applications where temporary anchoring is required. By way of example, the ground anchor can be particularly suitable for tethering of animals, and for anchoring boats and other water craft at shore. In such applications, the ground anchor is particularly advantageous as it can be embedded entirely, or almost entirely, into the ground and therefore not present

an obstacle to persons in the vicinity, and also be subsequently removed. Ground anchors according to the invention can be used for anchoring tents and other structures, as well as for guy wires and the like. Further, ground anchors according to the invention can be used as footings for structures.

The ground anchors according to the invention can be used either with or without the lateral stabilisation devices.

Further, the lateral stabilisation devices may have application to ground anchors other than ground anchors of the type according to the present invention.

It should be appreciated that the scope of the invention, is not limited to the scope of the various embodiments described.

Modifications and improvements can be made without departing from the scope of the invention.

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.