AU2016101884A4 - Improvements in screw piles - Google Patents

Abstract

Abstract A screw pile end piece (10) comprises a body portion (12) having a first frusto-conical inwardly tapered portion (18) and a second tapered portion (20) tapering towards a tip (22) and a helical screw (30) in the form of a fin, the end piece (10) defining a central axis passing from one end of the body portion to the tip, wherein the angle of taper of the second tapered portion relative to the central axis is greater than the angle of taper of the first tapered portion. It is preferred that the maximum diameter of the body portion is less than half the maximum diameter of the fins of the end piece. ,33 I(0 H-A

Description

2016101884 26 Oct 2016 ι "Improvements in screw piles"

Technical Field [0001] The present application claims priority from Australian Provisional Patent Application No 2015904400 filed on 27 October 2015, the content of which is incorporated herein by reference.

Background [0002] Screw piles, also referred to as helical piles, are typically used for ground anchoring for creating foundations of varying depths. They include a shaft which is typically hollow and a screw or helix for screwing the pile into the ground by rotation of the shaft. The helix may simply comprise an annular flat plate welded at a specified pitch to the shaft. Such flat plate helixes are used across a wide range of loads with larger loads requiring big diameter plates and high installation torques. The number of helixes, their pitch, diameter and other characteristics are determined by various parameters, including the design load requirement in particular. It is also known to form longer tapered helical screws for use as screw piles.

[0003] Screw piles are most commonly used for houses and smaller commercial buildings, but can be used for larger buildings and structures and in a wide variety of other end use applications.

[0004] Typically, a screw pile will comprise a base pile, which includes the helix, and a number of extension piles which are connected to the base pile in series to make a screw pile of a desired length. The extension piles typically comprise tubular steel elements. As screw pile is turned, the helix is rotated which pulls the screw pile through the ground.

[0005] There are a number of known problems with existing plate screw piles. One problem occurs when the helical screw hits a rock or floating boulder. The helical 2016101884 26 Oct 2016 2 screw is installed to a minimum torque value and needs to be seated in dense ground materials or weathered rock. The boulder may prevent further movement of the helical screw pile to its intended depth. It is to be noted that the operator who is screwing the pile into the ground cannot see the helical screw, and may have very little idea of what sort of ground the screw pile is being driven through. Good screw piling operators develop a feel for a rotating pile and can work out/predict the type of material the helix is engaging. It is usual for a geotechnical survey to be conducted on site with a bore log setting out the material occurring at different depths to assist the operator.

[0006] One further problem is that the screw pile may not be able to efficiently transfer the load that the tubular steel elements can bear to the ground. Typically, plate helixes that are circumferentially welded to a shaft can only support 50% to 60% of the design strength of the shaft. A cast multi-turn helix that is butt-welded to the end of the shaft can however support 100% of the design strength of the shaft.

[0007] It is one particular aim of the present invention to provide an end piece for helical screw pile which is more efficient in transferring load from the pile shaft to the ground.

[0008] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application.

[0009] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. 2016101884 26 Oct 2016 3

Summary [0010] According to a first aspect of the present invention there is provided a screw pile end piece comprising a body portion having a first frusto-conical inwardly tapered portion and a second tapered portion tapering towards a tip and a helical screw in the form of a fin, the end piece defining a central axis passing from one end of the body portion to the tip, wherein the angle of taper of the second tapered portion relative to the central axis is greater than the angle of taper of the first tapered portion.

[0011] Typically the angle of taper of the first tapered portion is preferably about 10°, and in the range of 5 to 15°. The angle of taper of the second tapered portion is greater and typically in a range from about 20 to 40°, and most typically about 30°.

[0012] It is preferred that the fin is tapered so that it is thickest nearest to the body portion and thinnest at the outer edge of the fin distal from the body. The preferred ratio of the thickness of the fin nearest the body to the thickness at the tip is 2::1. For example, in one preferred embodiment the fin may be about 16mm thick at the body and 8mm thick at its outer edge. The 2 to 1 ratio of the thickness of the fin nearest the body to the thickness at the tip is preferably maintained for the length of the fin for optimum transfer of load from the fin to the body portion.

[0013] Typically, the tapering is substantially present on the upper surface of the fin, in use, with the underside of the fin, facing the tip of the end piece being flat.

[0014] Thus in a related aspect of the present invention, there is provided a screw pile end piece comprising a body portion tapering towards a tip and a helical screw in the form of a fin extending around the body portion wherein the fin is tapered so that it is thickest nearest to the body portion and thinnest at the outer edge of the fin distal from the body and wherein the tapering is substantially only present on the upper surface of the fin, in use, with the underside of the fin, facing the tip being flat. 2016101884 26 Oct 2016 4 [0015] According to a third aspect of the present invention there is provided a screw pile end piece comprising a body portion and a helical screw in the form of a fin extending around the body portion, the end piece defining a central axis passing from one upper end of the body portion to the tip, wherein the plane of the fin is at an angle of 93 to 96° relative to the central axis, measured from the upper end of the end piece.

[0016] In a preferred embodiment, the edge of the helical screw closest to the tip has a bevel cutting edge. The cutting edge may have a height of about 3mm rising to the full thickness of the fin.

[0017] It is preferred that the upper end of the end piece defines a shoulder which is greater in diameter than the first frusto-conical portion.

[0018] It is preferred that the maximum diameter of the of the body portion is less than half the maximum diameter of the end piece defined by the maximum diameter if the fin.

Brief Description of Drawings [0019] Specific embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings in which:-

Figure 1 is a side view of a first embodiment of an end piece for a helical screw embodying the invention;

Figure 2 is a top plan view of the end piece for a helical screw shown in Figure 1; Figure 3 is a cross-section through the end piece for a helical screw shown in Figure 1; Figure 3a is a detail view of area D shown in Figure 3;

Figure 4 is a pictorial view of the end piece shown in Figure 1; 2016101884 26 Oct 2016 5

Figures 5a and 5b are detail views of area C shown in Figure 1 illustrating the cutting edge of the tip of the end piece;

Figure 6 is a side view illustrating the flat bottom of the flute; and

Figure 7 is a schematic illustration of a “bulb effect” when the multi-turn helical screw is in use;

Description of Embodiments [0020] As used in the specification, the terms upper and lower refer to the orientation of the end piece for a screw pile in normal use and are not intended to limit the screw pile to use in any particular orientation.

[0021] Referring to the drawings, Figures 1 to 6 show an end piece 10 for a screw pile. Note that the drawings omit the tubular steel element which in use is attached to the end piece and which will include a coupling for connection to other tubular elements to form an extension pile of a required length.

[0022] The end piece comprises a central body portion 12. The body portion includes a first end 14 which may be welded or otherwise fixed to an extension pile, typically in the form of a tubular steel element. The body portion 12 includes a stepped shoulder portion 16 adjacent the first end which has a greater diameter than the rest of the body portion. In the described embodiment, the maximum diameter of the shoulder portion is 178mm, although the actual dimensions of the end piece may be varied depending on the design load to be supported.

[0023] As oriented in Figure 2, and as is best seen in Figure 3, below the shoulder portion there is a first generally frusto-conical portion 18 having a first generally shallow angle of taper (typically around 10°) relative to the central axis A of the body portion and a second conical portion 20 leading to the tip 22 of the end piece which has a greater angle of taper than the portion 18, which as shown is about 30°. The 2016101884 26 Oct 2016 6 maximum diameter of the first frusto-conical portion is about 40 to 50mm less than the maximum diameter of the shoulder portion.

[0024] A helical fin 30 extends around the body portion. As is best seen in Figure 3a, the fin 30 is tapered so that it is thickest nearest to the body portion 12 and thinnest at the outer edge of the fin 30A distal from the body. Where the fin connects with the body portion is radiussed. At the top of the body portion where the helix is largest, the radius is typically about 15mm. Nearer to the tip, the radius is typically around 10mm. In the embodiment shown, the thickest part of the fin has a thickness Ti of about 16mm and at the tip the thickness T2 is 8mm.

[0025] The fin diameter measured from the central axis A is constant for the first full turn/revolution of the helix through 360° and then its diameter gradually reduces. The first full turn acts as single flat plate helix, discussed in the introduction above, in that it provides a calculable area of bearing surface with which to transfer the pile load into the ground. As shown in Figure 1, measured from the central axis A, β the angle of taper of the outside edge of the lower turns of the fin is 40° [0026] With reference to Figure 3 in particular, it can be seen that the fin 30 extends downwards, as well as away from the central axis A of the end piece. It can also be seen that the fin 30 does not extend as far as the shoulder 16. The angle a as shown in Figure 3 measured from the plane of the fin to the central axis is about 93°, but could be in the range of 93 to 96° due to manufacturing tolerances.

[0027] The leading edge of the fin 30 has a bevel edge 34 (best seen in Figures 4 and 5b). In particular the bevel edge includes a tip or blade which is narrower in thickness than the main part of the fin. This blade assists in the penetration of the helical screw into the ground, particularly heavily grassed ground. The height of the blade is typically about 3mm at the leading edge 36. As is best seen in Figure 4 the thickness of the blade increases away from the leading edge. 2016101884 26 Oct 2016 7 [0028] It is to be noted with reference to Figure 3a, that the taper of the fin is not the same on the top and bottom sides of the fin. In particular, the taper of the fin is generally all on the upper side of the fin with the lower side being flat and parallel to the 93° angle a.

[0029] It is preferred that the maximum diameter of the body portion is less than half the maximum diameter of the fins of the end piece. In other words if the maximum diameter of the fin of the helix is 300 mm, the maximum diameter of the body portion should be less than 150 mm.

[0030] In use, a screw pile of the desired length is assembled from the end helix and a plurality of connected hollow shafts. The shaft is rotated and the screw pile is screwed into the ground. As discussed above, the first full turn of the fin acts as single flat plate helix discussed above in that it provides a calculable area of bearing surface with which to transfer the pile load into the ground. The subsequent fin portion having a reduced diameter causes dense materials such as clays and sands to compact between the flights of the fin and creates a solid conical mass.

[0031] This mass compression effect is also assisted by the fact that the fin extends slightly downwards as well as outwards and by the slight conical taper of the upper portion 18 of the body of the end piece and the larger taper of the of the lower portion 20. As load is applied from above to this mass, the load is transferred not just directly down but is also transferred partially horizontally and outwardly therefore transferring a much greater load. The load is dissipated in a bulb shape and this “bulb effect” is illustrated in Figure 7. The bulb effect improves the efficiency of the multi-turn helix compared to a single plate helix typically, having the same load bearing performance of a single plate helix of around twice the diameter of the multi-tum helix, in all dense/very dense clays, sands and weathered rock.

[0032] As well as enhancing the bulb effect, the 93 to 96° angle of the fin improves the cut of the fin into ground and helps to pull the helix downwards, dislodge floating rocks, shale and boulders as it penetrates the ground. 2016101884 26 Oct 2016 8 [0033] The end piece will typically be manufactured in cast steel or cast iron.

[0034] It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims (11)

1. CLAIMS:

   1. A screw pile end piece comprising a body portion having a first frusto-conical inwardly tapered portion and a second tapered portion tapering towards a tip and a helical screw in the form of a fin, the end piece defining a central axis passing from one end of the body portion to the tip, wherein the angle of taper of the second tapered portion relative to the central axis is greater than the angle of taper of the first tapered portion.
2. 2. A screw pile end piece as claimed in claim 1 wherein the angle of taper of the first tapered portion is in the range of 5 to 15°, most preferably about 10°.
3. 3. A screw pile end piece as claimed in claim 1 or claim 2 wherein the angle of taper of the second tapered portion is greater than the angle of taper of the first tapered portion and is in a range from about 20 to 40°, and most typically about 30°.
4. 4. A screw pile end piece as claimed in any preceding claim wherein the fin is tapered so that it is thickest nearest to the body portion and thinnest at the outer edge of the fin distal from the body.
5. 5. A screw pile end piece as claimed in claim 4 wherein the ratio of the thickness of the fin nearest the body to the thickness at the tip is about 2::1.
6. 6. A screw pile end piece as claimed in claim 4 or claim 5 wherein the tapering is substantially present on the upper surface of the fin, in use, with the underside of the fin, facing the tip of the end piece being flat.
7. 7. A screw pile end piece comprising a body portion tapering towards a tip and a helical screw in the form of a fin extending around the body portion wherein the fin is tapered so that it is thickest nearest to the body portion and thinnest at the outer edge of the fin distal from the body and wherein the tapering is substantially only present on the upper surface of the fin, in use, with the underside of the fin, facing the tip being flat.
8. 8. A screw pile end piece comprising a body portion and a helical screw in the form of a fin extending around the body portion, the end piece defining a central axis passing from one upper end of the body portion to the tip, wherein the plane of the fin is at an angle of 93 to 96° relative to the central axis, measured from the upper end of the end piece.
9. 9. A screw pile end piece as claimed in any preceding claim wherein the edge of the helical screw closest to the tip has a bevel cutting edge.
10. 10. A screw pile end piece as claimed in claim 8 wherein the upper end of the end piece defines a shoulder which is greater in diameter than the first frusto-conical portion.
11. 11. A screw pile end piece as claimed in any preceding claim wherein the maximum diameter of the end piece, defined by the maximum diameter of the fin, is at least twice the maximum diameter of the body portion.