IMPROVED SCREW PILE FIELD OF THE INVENTION 5 The present invention relates to an improved screw pile. BACKGROUND TO THE INVENTION Screw piles are used in the construction of buildings and other structures. A 10 typical screw pile comprises a shaft, normally made from mild steel or a higher strength steel. A helical screw or blade is attached to the shaft. In order to insert the screw pile into the ground, the screw pile is rotated and pressed downwardly which causes the helical blade to bite into the ground and to screw into the ground. Once the screw pile has been properly inserted into the ground, the weight borne by the screw pile is 15 distributed from the helical blade into the earth that lies underneath the helical blade. Further, the earth positioned above the helical blade assists in resisting any lifting forces applied to the screw pile and thereby assists in maintaining the screw pile in the ground. Conventional screw piles comprise a single helical blade. The blade has a leading 20 edge that moves through and breaks the earth as the screw pile is screwed into the ground. Conventional screw piles have a leading edge on their blade that extends generally perpendicularly to the outer periphery of the blade (when viewed from above). As the shaft is normally cylindrical in shape, the leading edge of the blade may be considered to extend outwardly from the shaft in the radial direction. 25 Throughout this specification, the term "comprising" and its grammatical equivalents shall be taken to have an inclusive meaning unless the context of use indicates otherwise. 30 The applicant does not concede that any prior art to cutting the specification forms part of the common general knowledge in Australia or elsewhere.
2 BRIEF DESCRIPTION OF THE INVENTION According to one aspect of the present invention, there is provided a blade for a screw pile, the blade including: 5 a first straight edge portion for extending from a shaft of the screw pile; and a second straight edge portion forming an obtuse angle with said first straight edge portion. Preferably, the first straight edge portion extends from a shaft of the screw pile. The first 10 straight edge portion may extend radially from the shaft. A third straight edge portion may form an obtuse angle with the second straight edge portion. A fourth straight edge portion may form a right angle with the third straight edge portion. The first and fourth and straight edge portions may be parallel. The blade may be 15 symmetric. According to another aspect of the present invention, there is provided a screw pile including a shaft, and two blades in the form of opposing flat plates extending outwardly from the shaft, each blade having a first straight edge portion extending from the shaft 20 and a second straight edge portion forming an obtuse angle with said first straight edge portion. BRIEF DESCRIPTION OF THE DRAWINGS 25 Figure 1 shows a perspective view of a screw pile in accordance with one embodiment of the present invention; Figure 2 shows a plan view of the screw pile shown in figure 1, but only showing one blade for clarity purposes; 30 Figure 3 is a plan view of the screw pile as shown in figure 1; 3 Figure 4 is an underneath view of the screw pile shown in figure 1; Figure 5 is a perspective view of a screw pile in accordance with another 5 embodiment of the present invention; Figure 6 shows a plan view of the screw pile shown in figure 5, but only showing one blade for clarity purposes; 10 Figure 7 is a plan view of the screw pile as shown in figure 5; Figure 8 is an underneath view of the screw pile shown in figure 5; Figure 9 is a perspective view of a screw pile in accordance with another 15 embodiment of the present invention; Figure 10 is a side view of one of the blades used in the screw pile shown in figure 9; 20 Figure I 1 shows a plan view of the screw pile shown in figure 9, but only showing one blade for clarity purposes; Figure 12 is a plan view of the screw pile as shown in figure 9; 25 Figure 13 is an underneath view of the screw pile shown in figure 5; Figure 14 shows a plan view of a screw pile in accordance with a further embodiment of the present invention; 30 Figure 15 is a view of a plate that has been cut to shape for use as a blade on a screw pile in accordance with an embodiment of the present invention; and 4 Figure 16 is a plan view of a blade for a screw pile in accordance with another embodiment of the present invention. 5 DETAILED DESCRIPTION OF THE DRAWINGS It will be understood that the drawings have been provided for the purpose of illustrating embodiments of the present invention. Therefore, it will be appreciated that the present invention should not be considered to be limited solely to the features as 10 shown in the drawings. Figures 1 to 4 show various views of a screw pile in accordance with an embodiment of the present invention. The screw pile shown in figures 1 to 4 is designed for use in sandy soils or other soils that are easily friable. The screw pile 10 shown in 15 figures I to 4 comprises a shaft 12. Shaft 12 is a generally cylindrical shaft that may be made from mild steel or a higher strength steel. The shaft 12 may be a hollow shaft. The shaft 12 has an upper end 14 and a lower end 16. Two driving lugs 18, 20 (see figure 3) are attached to the shaft near the upper end 16. The driving lugs 18, 20 engage with a driving mechanism to facilitate screwing of the screw pile 10 into the ground. 20 The screw pile 10 also includes two blades 22, 24. As best shown in figure 1, the blades 22, 24 mounted to the outer periphery of the shaft 12, with each blade being mounted at opposed angles to the longitudinal axis of the shaft 12. Each of the blades 22, 24 comprises a flat plate. 25 The lower end 16 of the shaft includes an attack bit formed by points 26, 28. During installation of the screw pile 10 into the ground, the attack bit contacts the ground before any other part of the screw pile. The attack bit bites into the ground and assists in maintaining the screw pile in the desired location of installation. 30 5 Once the attack bit has penetrated a short way into the ground, the blades 22, 24 of the screw pile 10 then engage with the ground and also dig into the ground. This causes the screw pile 10 to screw into the ground. Rotation of the screw pile 10 continues until the screw pile has been screwed to the desired depth. 5 Figure 2 shows a plan view of the shaft 12 and the blade 24. The blade 24 has a leading edge, generally indicated by reference numeral 30. The direction of rotation of the blade 24 is shown by the arrow in figure 2. The leading edge 30 is the part of the blade 24 that contacts the earth as the blade 24 is rotated during insertion of the screw 10 pile 10 into the ground. Therefore, the leading edge 30 engages with and breaks the earth as the screw pile is screwed into the ground. The leading edge 30 includes a first portion 32, a second portion 34 and a third portion 36. First portion 32 is located adjacent to the shaft 12. First portion 32 extends generally perpendicularly to the outer periphery of the shaft 12. In this regard, first portion 32 of the leading edge of blade 24 may be 15 considered to extend in the radial direction from the shaft 12. The second portion 34 of the leading edge 30 sweeps back from the first portion 32. Similarly, the third portion 36 sweeps back from second portion 34. In this way, if the second portion or the third portion contact rocks or other detritus or hard material 20 during screwing in of the screw pile 10, the swept back angle of those portions of the leading edge assist in removing or deflecting the rocks or hard material, thereby facilitating insertion of the screw pile 10 into the ground and minimising the likelihood of damage to the screw pile or to the equipment used to screw in the screw pile. 25 The first portion 32 of the leading edge 30 may be considered to comprise a small and strong initial straight blade attack region. The second portion 34 may be considered to comprise a medium follow-on, swept blade attack region. The third portion 36 may be considered to comprise the largest follow-on, increased sweep blade attack region. 30 It also can be seen from figure 2 that the rear part 38 of blade 24 is of generally square or rectangular shape.
6 The other blade 22 of screw pile 10 has a generally similar arrangement at its leading edge and rear part. 5 Figures 5 to 8 show another embodiment of a screw pile 50 in accordance with the present invention. The embodiment shown in figures 5 to 8 is very similar to the screw pile 10 shown in figures I to 4. For convenience, similar features will be referred to using similar reference numerals, but with the attachment of a '. These features need not be described further. The screw pile 50 shown in figures 5 to 8 is designed primarily for 10 use in clay soils. The screw pile 50 as shown in figures 5 to 8 differs from the screw pile 10 as shown in figures I to 4 in that the width of the blades is less. In particular, the blade 24' shown in figures 5 to 8 has a width W that is less than the width W of the blade 24 shown 15 in figures I to 4. The reason for this is that the screw pile 10 is designed for use in sandy soil sites. As these soils are easily broken, the additional width of blade 24 does not cause difficulties in screwing the screw pile 10 into the soil. Further, the additional width of blade 24 (and the corresponding blade 22 that is also mounted to the shaft 12) assists in spreading the load from the screw pile into the friable soil. In contrast, the narrower 20 blade 24' shown in figures 5 to 8 provides good penetration into firm to hard clay soils. Firm to hard the clay soils provide good geotechnical support and the blades 22' and 24' are optimised to provide the best load characteristics in those soils. Although not shown in any of figures 1 to 8, the blades on screw pile 10 may also be thinner than the blades on screw pile 50. 25 Figures 9 to 13 shown various views of a screw pile 60 in accordance with another embodiment of the present invention. The screw pile 60 has a number of features in common with the screw pile 10 as shown in figure 1 and, for convenience, those similar features are denoted by a similar reference numeral is but with the addition of a 30 These features need not be described any further.
7 The screw pile 60 is intended for use in rocky soils. Accordingly, compared to screw piles 10 and 50, as shown in figures 1 to 8, the screw pile 60 has blades of lesser width. The blades 22" and 24" are also thicker than the blades 22, 24 and 22', 24'. As shown in figure 10, the blade 22" also has a bevelled leading edge 23, which assists in 5 breaking or penetrating the ground.in advance of the leading edge during screwing in of the pile 60, as well as enhancing the deflection capabilities of the blades 22" and 24". A further difference is that the front part of the blade 24" includes first portion 32", second portion 34", third portion 36" and fourth portion 37. The first portion 32" 10 comprises a small and strongest initial straight blade attack region, the second portion 34" provides a medium follow-on, swept blade attack region, the third portion 36" provides a larger follow-on, increased sweep blade attack region and the fourth region 37 provides a trailing edge blade to help final deflection of rocky material. The blade 22" has a similar leading edge region. 15 The rear part 38" also has a trailing blade region 39 for load distribution. The trailing blade region 39 may be expediently formed by simply cutting off a corner of the rear part of the blade. 20 The embodiment of the screw pile 60 shown in figures 9 to 13 has the smallest and thickest blade with added cutting and deflection in the blades. This version of the screw pile is designed to penetrate the most difficult soil that contains rocks, debris and cobbles. This version is less reliant on blade load capacity than the versions shown in figures 1 to 8 since it is designed to chase and engage bedrock. 25 Figure 14 shows a plan view of a screw pile in accordance with a further embodiment of the present invention. The screw pile 100 shown in Figure 14 has a shaft 102 and two blades, designated in Figure 14 as Blade A and Blade B. Blade A has a leading edge 104 that includes first attack edge portion 106, second attack edge portion 30 108 and third attack edge portion 110. Similarly, blade B has a leading edge 112 that 8 includes first attack edge portion 114, second attack edge portion 116 and third attack edge portion 118. Blade A has a trailing edge 120 having edge portion 122 and swept back edge 5 portion 124. The trailing edge 120 joins to the shaft 102 via a perpendicular portion that is located adjacent to edge portion 114 of leading edge 112 of Blade B, in the view shown in Figure 14. Blade B has a trailing edge 130 having edge portion 132 and swept back edge portion 134. The trailing edge 130 joins to the shaft 102 via a perpendicular portion that is located adjacent to edge portion 106 of leading edge 104 of Blade A, in the view 10 shown in Figure 14. It will be appreciated that the trailing edge of one blade is at a different vertical height to the leading edge of the other blade. As can be seen from figure 14, the trailing edge of each blade mirrors the leading edge of the other blade to create a "wide and opening between the blades to prevent rocks 15 and to debris jamming therebetween. These white and openings are shown by reference numerals 140 and 142. The swept trailing blade edges also aid in deflecting any rocks or debris that attempt to jam between the blades. Figure 15 shows a steel plate 150 that has been cut to a shape that is suitable for 20 use as a blade on a screw pile in accordance with the embodiment of the present invention shown in Figure 14. The plate 150 is made from 8 mm thick, 350 grade steel, although it will be appreciated that the plate may be made from different grades and/or thickness of steel or indeed it may be made from other alloys or materials. The plate 150 has leading edge portions 152, 154 and 156, and trailing edge portions 158, 160 and 162. 25 The plate has a side edge 164. A half oval cut 166 is made to allow the blade to closely conform to the outer periphery of the shaft of the screw pile, it being appreciated that the plate is mounted to the shaft at an angle to the horizontal (thereby necessitating a half oval cut). As can be seen from Figure 15, the trailing edge is a mirror of the leading edge. 30 According to another aspect of the present invention ,there is provided a screw pile blade 200 as shown in Figure 16. The blade 200 has a leading edge 202 that contacts 9 earth as the screw pile is screwed into the ground. The leading edge 202 includes a first straight edge 204 portion for radially extending from a shaft of the screw pile, and a second straight edge portion 206 forming an obtuse angle 207 with said first straight edge portion 204. A third straight edge portion 208 forms an acute angle 209 with the second 5 straight edge portion 206. As can be seen from Figure 16, the trailing edge 210 mirrors the leading edge 202. The blade 200 is effective in working clay and cobbled soils. Screw piles in accordance with embodiments of the present invention provide robust screw piles having enhanced installation capabilities. The use of twin blades 10 evens out the forces that are applied to the blade during installation of the blade into the ground. Further, loads borne by the screw pile are evenly distributed through the twin blades into the ground. In embodiments where the blades are formed from flat plates, the blades are easily made by cutting or stamping and the blades can be very simply joined to the shaft of the screw pile by welding. Some embodiments of the screw pile include 15 attack points or an attack bit on the end of the shaft, which also assists in keeping the pile aligned during installation and minimises oscillation of the screw pile during installation. Screw piles in accordance with various embodiments of the persent invention may also provide the following benefits: 20 * Unlike normal screw piles, the twin blade pile has 2 main sets of attack/embedment blades' for increased & balanced load distribution during and after installation, effectively doubling the engaged footprint * The pitched flat twin blades, provide counter balanced penetration into soil during installation 25 0 Each blades cutting edge provides 3 progressive stages of cut/embedment during ground penetration 0 Each blade provides swept progression to combat resistance for improved penetration, * As each blade rotates to engage - the swept angle increases relative to the 30 rotation 10 - The twin flat blades provide a square 'dual combined' end bearing plate for compression & tension loads * The trailing edge of each blade mirrors the leading edge of the opposite blade to create a 'widened opening' between the blades to prevent rocks 5 and debris jamming. The swept trailing blade edges also aid in deflecting any rocks or debris that attempt to jam between the blades. * The pile components and design, provide a simple & cost effective manufacturing process 10 Those skilled in the art will appreciate that the present invention may be susceptible to variations and modifications other than those specifically described. One possible variation of the screw pile may involve the addition of a further set of twin blades above and spaced from the lower twin blades that are shown in figures I to 13. These further twin blades are suitably mounted in similar fashion to the shaft of the screw 15 pile. In this embodiment, the earth that is present between the lower set of twin blades and the upper set of twin blades is trapped between the two sets of blades. As a result, the screw piles in accordance with that embodiment act in a fashion that is similar to friction piles. 20 In other embodiments, the flat plate twin blades, as shown in figures I to 13, may be replaced by helical twin blades or twin helical flights. It will be understood that the present invention encompasses all variations and modifications that fall within its spirit and scope.