GB2412686A

GB2412686A - A screw pile with fins

Info

Publication number: GB2412686A
Application number: GB0505558A
Authority: GB
Inventors: Duncan Mcgregor; Peter Dunn
Original assignee: Screwfast Foundations Ltd
Current assignee: Screwfast Foundations Ltd
Priority date: 2004-03-30
Filing date: 2005-03-18
Publication date: 2005-10-05
Anticipated expiration: 2025-03-18
Also published as: GB0407082D0; GB0505558D0; GB2412686B

Abstract

A screw pile includes a shaft 10 and at least one helix 12. A pair of diametrically opposed fins 15 extend outwardly from the shaft 10 to create a void 18 around the shaft 10 which may be filled with concrete to further anchor the pile. The fins 15 may be made from a material adapted to bend on rotation of the shaft 10.

Description

24 2686 A SCREW PILE ANI) METHOD OF INSTALLATION THIS INVENTION concerns

screw piles adapted to penetrate the ground to serve as an anchor to support tension or compression loads. Such anchors are used, for example, to secure street signs, telegraph poles, telecommunication masts, and the like.

It is known to provide a screw pile comprising a shaft having one or more helices welded thereto acting as screw threads to cause the pile to penetrate the ground upon the application of torsion to the shaft. Torsion is applied to the head of a shaft and the helices screw into the ground without the need to exert a large downwards force. The applied torque is typically proportional to the pull-out force which the anchor is required to resist.

Such devices can be used also to resist compression loads.

The shaft may include a series of apertures or other means for connection of the driving mechanism and of a structure such as a mast to the top of the screw pile.

Structures typically have little inherent weight but must resist horizontal loads such as wind forces.

In cases where a screw pile is driven into soft ground there is a risk that horizontal forces subsequently applied to the mounted structure may cause some lateral movement of the top of the shaft in use. It is an object of the present invention to provide a screw pile and a method of installation which will prevent such upper- end movement of a screw pile shaft.

According to the present invention there is provided a screw pile comprising a shaft, at least one helix mounted on the shaft to act as a screw thread to cause the screw pile to penetrate the ground upon rotation of the shaft, and at least one fin extending radially from the shaft.

There may be a pair of fins extending radially from the shaft at diametrically opposed positions thereon.

The helix may be mounted on the shaft at the lowermost or leading end region of the shaft while the or each fin may be located thereon at an upper or an opposite end region thereof.

Two or more pairs of fins may be mounted on the shaft at longitudinally spaced positions thereon.

The diametrical extent of the or each fin from the longitudinal axis of the shaft may be substantially the same as that of the helix.

The or each fin may have a portion of uniform radial extent from the shaft and a portion of reducing radial extent at the lower most or leading end of the fin.

The or each fin may be of a material adapted to bend upon rotation of the shaft, in response to the resistance of the surrounding ground into which the shaft is inserted.

Further according to the invention, there is provided a method of installation of a screw pile comprising a shaft, at least one helix mounted on the shaft to act as a screw thread to cause the screw pile to penetrate the ground upon rotation of the shaft, and at least one fin extending radially from the shaft; the method comprising the steps of rotating the shaft in engagement with the ground, causing, by such rotation, the or each fin to penetrate the ground to create a void around the shaft, and filling the void with a gettable material.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig 1 illustrates a screw pile installed within the ground; and Fig 2 is a plan view.

The screw pile comprises a shaft generally indicated at 10, which may be of tubular construction, usually of steel, and has a lowermost penetrating end 11 and at least one helix 12 located close to the lowermost end 11 of the shaft which, upon rotation of the shaft pulls the screw pile into the ground.

Two or more helixes 12 may be provided at space locations along the shaft, each helix taking approximately one turn around the shaft and being produced from a disc which is cut radially and twisted into a helix, then welded to the outer surface of the shaft. If several helixes are provided they may be of increasing diameter upwardly from the lowermost helix.

At the upper end of the shaft 10 a series of apertures 13 are provided for attachment of a rotary tool for applying the rotational torque during installation of the screw pile, and for attachment to the screw pile of a mast such as is illustrated at 14.

Other attachment means may be provided such as bolted flanges on the screw pile and mast respectively.

Located close to the upper end of the shaft 10 in accordance with the invention, is a pair of steel fins 15 welded at diametrically opposed positions on the shaft thus to extend outwardly from the longitudinal axis thereof to an extent similar to that of the helix 12, and determined by the expected horizontal load on the pile, and the strength of the ground.

Each fin 15 comprises an upper portion 16 of uniform radial extent and a lower portion 17 of reducing radial extent to the lowermost point of attachment of the fin to the shaft. s

In use, the screw pile is driven into the ground by rotation using a driving mechanism (not shown) attached, for example, by way of the apertures 13. During the final stages of penetration of the screw pile the fins 15 engage the ground and serve to force the surrounding ground outwardly to create a void 18 around the shaft 10. The void is filled with a gettable material such as sand, cement, gravel and water in a controlled manner as the void deepens. The fins 15 serve as mixing paddles to produce a concrete lump surrounding the screw pile to the depth of penetration of the fins.

If required, the fins may be at a position part way along the shaft, and several pairs of fins may be provided at longitudinal spaced locates thereof according to the required depth of the concrete lump.

It will be appreciated that ground consistencies vary considerably, and so the radial extent, thickness, depth and location of the fins are selected accordingly. In soft ground the fins will retain their radial extent, but in harder ground they may bend as shown at lSa in Fig 2, thus producing a void of lesser diameter and so a smaller lump is created. This is no disadvantage and actually produces a saving of materials in harder ground where a lesser diameter lump is needed. Thus, the bending of the fins provides a degree of control over the passive resistance of the concrete lump such that in softer soils the full extent of concrete is introduced which, at the top of the screw pile provides stability for the structure to be mounted thereon and increased resistance to horizontal forces applied to the structure in use. s

In another example, the fins 15 may be provided in sets of three or more such fins extending radially from the shaft at the same longitudinal position thereon.

Claims

1. A screw pile comprising a shaft, at least one helix mounted on the shaft to act as a screw thread to cause the screw pile to penetrate the ground upon rotation of the shaft, and at least one fin extending radially from the shaft.

2. A screw pile according to claim 1 including a pair of fins extending radially from the shaft at diametrically opposed positions thereon.

3. A screw pile according to claim 1 or claim 2 wherein the helix is mounted on the shaft at the lowermost or leading end region of the shaft while the or each fin is located thereon at an upper or opposite end region thereof.

4. A screw pile according to any preceding claim including two or more pairs of fins mounted on the shaft at longitudinally spaced positions thereon.

5. A screw pile according to any preceding claim wherein the diametrical extent of the or each fin from the longitudinal access of the shaft is substantially the same as that of the helix.

6. A screw pile according to any preceding claim wherein the or each fin has a portion of uniform radial extent from the shaft and a portion of reducing radial extent at the lowermost or leading end of the fin.

7. A screw pile according to any preceding claim wherein the or each fin is of a material adapted to bend upon rotation of the shaft, in response to the resistance of the surrounding ground into which the shaft is inserted.

8. A method of installation of a screw pile comprising a shaft, at least one helix mounted on the shaft to act as a screw thread to cause the screw pile to penetrate the ground upon rotation of the shaft, and at least one fin extending radially from the shaft; the method comprising the steps of rotating the shaft in engagement with the ground, causing by such rotation the or each fin to penetrate the ground to create a void around the shaft, and filling the void with S a gettable material.

9. A method according to claim 8 wherein the gettable material is introduced into the void during rotation of the shaft.

10. A method according to claim 8 or claim 9 wherein the or each fin, during rotation of the shaft, serves as a paddle to mix the gettable material.

11. A method according to any one of claim 8 to 10 wherein the gettable material is a cementitious material.