AU783773B2 - Variable displacement pile former - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: Actual Inventors: Address for Service: John Wagstaff Constructions Pty Ltd Roderic Thomas Campbell.

John Paul Wagstaff CULLEN CO., Patent Trade Mark Attorneys, 239 George Street, Brisbane, QId. 4000, Australia.

Variable Displacement Pile Former Invention Title: Details of Associated Provisional Applications: Australian Patent Application No.

PR0956 filed 24 October 2000.

The following statement is a full description of this invention, including the best method of performing it known to us: 2 THIS INVENTION relates to a method and apparatus for forming a pile. In particular, the invention is directed to a method and apparatus for forming a pile which is selectively variable along its length between a displacement pile and a non-displacement pile.

BACKGROUND ART There are various known types of concrete piles. For example, concrete piles may be precast, or cast in place. Precast piles are usually hammered into the ground. Such piles are known as "displacement" piles as the surrounding soil is displaced to accommodate the passage of the pile into the soil. On the other hand, piles which are cast in place are often so-called "non-displacement" piles as the concrete is poured into predrilled bores or tubes from which the soil has been removed. Hence the surrounding soil is not displaced by the pile. Displacement piles have greater pile bearing capacity due to greater skin friction and greater end bearing between the pile and the displaced surrounding soil.

It is also known to form displacement piles in situ. Such displacement piles are formed by drilling a pile former into the ground. The pile former may have a screw thread or flight at its leading end and/or along 20 its periphery to facilitate drilling into the ground and to form one or more helical grooves in the ground surrounding the pile former. As the pile former is drilled into the ground, it displaces the soil outwardly, thereby compressing it.

Once the pile former has been drilled to the desired depth, the pile former is then gradually removed from the ground. As the pile former is being withdrawn from the ground, concrete is passed through an axial bore in the pile former and into the bore left behind by the pile former. Examples of such pile formers can be found in Australian patent no. 668978, and U.S. patents nos. 5,722,498; 5,875,860 and 6,033,152.

In order to form a displacement pile in place, the pile former S* 30 must be able to displace the soil laterally outwardly as it is driven or drilled into the ground. Some soils are so highly compacted that it is not feasible to use a displacement pile former. Other soils may permit displacement pile forming to a certain depth, but a subterranean layer of compacted soil may prevent further drilling by the pile former. The bore formed by the pile former may not be of sufficient depth to provide the required bearing capacity.

Hitherto, in such cases, it has not been possible to use displacement pile formers and piling contractors have had to resort to non-displacement piles.

Since non-displacement piles have less bearing capacity than displacement piles, a higher number of non-displacement piles is normally required to meet design requirements.

It is an object of the present invention to provide a method and apparatus for forming a variable displacement pile which overcomes or ameliorates the abovedescribed disadvantage of known pile formers, or which at least provides a useful choice.

SUMMARY OF THE INVENTION In one broad form, the invention provides apparatus for forming a variable displacement pile, comprising a tubular displacement head adapted to be driven or drilled into the ground to form a bore where the pile is to be formed in place, the head having an outlet at or adjacent its lower end, and an 20 axial passage through the head communicating with the outlet to permit cementitious material to be passed through the head and outlet into the bore, as the head is withdrawn from the ground, and the head further having an internal conveying mechanism and an aperture communicating with the conveying mechanism, whereby ground 25 material may pass through the aperture and be conveyed upwardly through l the tubular head by the conveying mechanism.

The ground material may be soil, mud, sand, earth, rubble or the like. For simplicity, the ground material may be referred to simply as "soil" in this specification but that term is intended to cover all suitable ground material.

4 4 The apparatus, in effect, is a novel combination of a displacement pile former and a non-displacement pile former. The displacement head can be used in a conventional manner to displace the ground material laterally and create a bore in which a displacement pile can be formed. However, if the displacement head encounters hard or compacted soil which it is unable to displace laterally, the soil can be conveyed upwardly within the displacement head by the conveying mechanism. The extracted soil may be conveyed to the surface, or passed out through apertures in the head at a higher level where the soil is not as hard and can therefore be displaced laterally or compacted.

The apparatus of this invention is particularly useful in situations where a layer of hard or compacted soil is encountered while drilling. Only the soil in that layer need be removed by the conveying mechanism to permit the displacement head to pass through that layer. Thereafter, the conveying mechanism can be deactivated, and the displacement head used for lateral soil displacement to continue to form a displacement pile.

In another form therefore, the invention provides a method of using the above apparatus to form a variable displacement pile, comprising S.the steps of driving or drilling the displacement head into the ground to displace soil laterally and form a bore in which a displacement pile may be formed, and, as and when required, selectively operating the conveying mechanism to convey soil from the aperture in the displacement head upwardly inside the displacement head.

The resultant pile would then be a displacement pile except for the axial section(s) where the soil has been removed by conveying it through the displacement head. At such section(s), the pile would be akin to a nondisplacement pile. For the purpose of this patent specification, the resultant hybrid pile is referred to as a "variable" or "partial" displacement pile.

Typically, the displacement head is a steel drive tube. A 30 removable collar or sleeve may be provided at the leading end of the drive tube to provide a radially enlarged portion. Helical or part-helical flights may be provided around this enlarged section.

1.

A pivotable radial lug may also be provided on the outside of the collar to form a helical groove in the surrounding soil as the displacement head is drilled into the ground. When the displacement head is removed by rotating it still in the same direction, the lug may pivot so as to form a helical groove in the surrounding soil of minimum width. This groove is filled with cementitious material to enhance bearing capacity.

The conveying mechanism is suitably an auger mounted axially within the tubular displacement head.

The passage for the cementitious material is suitably a tube extending axially within the hollow displacement head. The auger may suitably be formed around that tube.

Suitable drive means are provided for relative rotation of the head and auger. In one embodiment, the auger is held by a brake while the displacement head is rotated therearound. In a second embodiment, the auger and displacement head are independently driven to provide relative rotation between them. The rotation of the auger relative to the head causes the soil at the aperture in the head to be conveyed upwardly.

Radial apertures may be provided at higher levels on the displacement head to permit the soil to pass out of the displacement head.

In order that the invention may be more fully understood and put into practice, preferred embodiments thereof will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS 25 Figs. 1A and 1B illustrate operation of a conventional pile **former, Fig. 2A is a part-sectional elevation of the displacement head of the pile forming apparatus of one embodiment of the invention, Fig. 2B is a fragmentary side elevation of the displacement head 30 showing a pivoting lug; Fig. 3 illustrates a separate drive mechanism for the auger of the displacement head of Fig. 2A, d0 6 Fig. 4 illustrates a brake mechanism for the auger of the drive head of Fig. 2A, Fig. 5 is an elevational view of the lower end of the displacement head of Fig. 2A, Fig. 6 is a part sectional-view of the lower end of the displacement head of Fig. 2A, and Fig. 7 illustrates schematically the steps in forming a bore for a variable displacement pile.

DESCRIPTION OF PREFERRED EMBODIMENTS As shown in Figs. 1A and 1B, a displacement pile is normally formed in situ by using a hydraulic motor 1 on a drilling rig to drill a soil displacement head 2 into the ground. The soil displacement head 2 is suitably mounted on a drive tube 3, and may be provided with helical flights. As the head 2 is drilled into the ground, it displaces the soil laterally and compacts it.

Once the desired depth has been reached, the displacement head is withdrawn from the soil. As it is being withdrawn, concrete is pumped through hose 4, the drive tube 3 and the displacement head 2, into the bore left behind, to thereby form a displacement pile in place.

Fig. 2A illustrates a soil displacement head suitable for forming a variable displacement pile, according to one embodiment of this invention.

The soil displacement head 9 comprises a steel drive tube 10 having a collar or sleeve 11 at its lower end to form a radially enlarged portion. The collar 11 is preferably replaceable. Since the collar 11 is the fastest wearing part, it can be replaced when worn without replacing the whole displacement head.

**One or more helical flight sections 12 may be provided on the displacement head, normally at its lower end. Radial apertures 16 are provided in the upper part of the drive tube The collar also has a pivoting elongated lug 17, as shown in Fig.

2B. When the displacement head 9 is drilled into the ground, the radial lug 17 forms a small helical groove in the surrounding soil. (This groove may subsequently collapse when the displacement head is removed).

4 7 Generally, the displacement head is removed while rotating it in the same direction as when it was inserted into the ground. By pivotally mounting the lug 17 at one end thereof about a radial axis 18, it is able to pivot such that as the displacement head is withdrawn, the lug forms a helical groove in the surrounding soil having a width equal to the short side width of the elongated lug 17. This helical groove is filled with concrete and increases the bearing capacity of the pile. (The lug 17 is omitted from Figs. 5 and 6 for clarity).

The displacement head 9 also has a concrete delivery tube 13 extending coaxially within the drive tube 10, and an auger 14 formed around the delivery tube 13. An aperture 15 is provided in the side of the collar 11 and tube 10 as shown in Figs. 2A and 6. When the displacement head is drilled into the ground, and there is no relative movement between the auger 14 and the drive tube 10, the aperture 15 quickly fills with soil and is effectively closed. However, if there is relative movement between the auger 14 and the drive tube 10, soil passing through the aperture 15 will be conveyed by the auger 14 along the inside of the drive tube As shown in Figs. 3 and 4, the drive tube 10 is normally driven by a hydraulic motor 20 (shown in block form in phantom outline) which forms 20 part of the drilling rig. Relative rotation between the auger 14 and the drive tube 10 can be obtained by using a separate drive motor 21 as shown in Fig.

3. The drive motor 21 rotates the tube 13 on which the auger 14 is formed, independently from the drive tube 10. By controlling the speed and direction of the motors 20, 21, relative rotation can be obtained between the auger 14 25 and the drive tube 10. Maximum relative rotation would be obtained by rotating the auger 14 in the opposite direction to the drive tube In an alternative embodiment, illustrated in Fig. 4, the auger 14 is normally allowed to rotate freely. (When the aperture 15 is clogged with soil, the auger 14 would normally rotate with the driven drive tube 30 However, when relative rotation between the auger 14 and the drive tube is required, a brake 22 is applied to the tube 13 on which the auger 14 is formed. With the auger 14 held still, and the drive tube 10 rotated, the relative 8 rotation between the two will cause material entering the aperture 15 to be conveyed by the auger within the drive tube The concrete outlet on the displacement head is shown in more detail in Fig. 5. A short pipe 24 is fitted to the lower end of the inner tube 13, and a drop-out plunger 25 is located within the pipe 24. The drop-out plunger is in the form of a tube having a pointed end 26 which locates in an annular seat 27 when the plunger is pushed up into pipe 24. The mating or seating surfaces of the plunger 25 and annular seat 27 are frustoconical to limit upward movement of the plunger. A bolt 28 is inserted through the pipe 24 and passes through two diametrically-opposite axial slots 29 in the plunger tube 25. In this manner, the plunger is able to "drop out" from the bottom of the displacement head, yet is still secured to the displacement head.

In use, as the displacement head 9 is drilled into the ground, the soil keeps the plunger 25 pushed up against its seat 27. When the displacement head is being withdrawn, and concrete is pumped through the inner tube 13, the pressure of the concrete forces the plunger to drop out, allowing the concrete to pass out of the displacement head through the annular space between the end 26 of the plunger and the seat 27.

The operation of the abovedescribed pile forming apparatus will now be described with reference to Fig. 7. To form a displacement pile, the displacement head is drilled into the ground, with no relative rotation between the internal auger 14 and the drive tube 10. As the displacement head is inserted into the ground, the collar 11 on the drive tube 10 displaces the soil laterally as shown schematically by the arrows in Fig. 7A.

If the displacement head encounters a layer of hard or compacted soil, such as compacted sand, indicated by the letter in Fig.

7B, the displacement head may not be able to move the soil in that layer laterally. In this event, the auger 14 is used to remove soil from that layer. The auger 14 is rotated relative to the drive tube 10 either by rotating it 30 independently of drive tube 10, or holding the auger 14 fixed while the drive tube 10 rotates around. The relative rotation (in the appropriate direction) of the auger 14 within the drive tube 10 conveys material from the aperture 0 9 up the inside of the drive tube 10 (as depicted by the arrows in Fig. 7B) from where it is discharged through the radial apertures 16. (Since the collar 11 forms a radially enlarged portion of the displacement head, the diameter of the bore formed by the displacement 10 will be slightly larger than the drive tube 10. The material conveyed from aperture 15 by auger 14 can be discharged through the radial aperture 16 into the space between the drive tube 10 and the bore formed by collar 11). By removing the soil from the hard layer X, the displacement head is able to pass through the layer without having to displace the soil laterally.

Once the displacement head has passed through the hard layer X, it can again be used as a displacement pile former as described above, with no relative rotation of the auger and the drive tube. Namely, below the hard layer X, the displacement head displaces the soil laterally as shown by the arrows in Fig. 7C.

Once the desired depth has been reached, the displacement head is then gradually withdrawn from the ground while pumping cementitious material such as grout or concrete into the bore formed by the head. The pile so formed will be a displacement pile along its length, apart from the area of the hard layer X where the pile is a non-displacement pile in nature. It will be apparent to those skilled in the art that when removing soil from the hard layer, not all the soil within the diameter of the collar 16 need be removed.

Partial removal may be sufficient to allow the remaining soil in the layer to be displaced laterally around the displacement head, in which case the s'ection of the pile in the hard layer would have properties somewhere between a nondisplacement pile and a full displacement pile.

The foregoing describes only some embodiments of the invention, and modifications which are obvious to those skilled in the art may be made thereto without departing from the scope of the invention. For example, the auger 14 may be used to convey material, such as stone, lime etc. down the drive tube and out through the aperture 15. This would allow coarse material to be inserted into the bore formed by the displacement head, which might not otherwise pass through the concrete outlet.

Claims (17)

1. Apparatus for forming a variable displacement pile comprising: a tubular displacement head adapted to be driven or drilled into the ground to form a bore where the pile is to be formed in place, the head having an outlet at or adjacent its lower end, and an axial passage through the head communicating with the outlet to permit cementitious material to be passed through the head and outlet into the bore, as the head is withdrawn from the ground, characterised in that the head has an internal conveying mechanism, and an aperture communicating with the conveying mechanism, whereby ground material may pass through the aperture and be conveyed upwardly through the tubular head by the conveying mechanism.

2. Apparatus as claimed in Claim 1 wherein the displacement head comprises a steel drive tube.

3. Apparatus as claimed in Claim 2 further comprising a removable collar at the leading end of the drive tube to form a radially enlarged portion of the displacement head.

4. Apparatus as claimed in Claim 3 further comprising helical or part-helical flights around the radially enlarged portion. 20 5. Apparatus as claimed in Claim 3 further comprising a lug pivotally e •mounted to the outside of the collar, the lug being pivotably about a radial axis of the displacement head.

6. Apparatus as claimed in any preceding claim wherein the aperture is formed in a peripheral portion of the displacement head at its leading end.

7. Apparatus as claimed in any one of the preceding claims further comprising a tube extending axially within the displacement head, the tube defining at least part of the passage for the cementitious material.

8. Apparatus as claimed in claim 7 wherein the conveying mechanism is a selectively operable auger mounted axially within the tubular displacement head.

9. Apparatus as claimed in claim 8 wherein the auger is formed around the tube. Apparatus as claimed in claim 8 or 9 further comprising drive means for creating relative rotation of the displacement head and auger. 11

11. Apparatus as claimed in Claim 10 wherein the drive means comprises separate drive mechanisms for the auger and the displacement head.

12. Apparatus as claimed in Claim 10 wherein the drive means comprises a drive mechanism for the displacement head and a brake mechanism for the auger.

13. Apparatus as claimed in any one of the preceding claims, further comprising radial apertures on the displacement head to permit ground material raised by the conveying mechanism to pass out of the displacement head.

14. A method of forming a variable displacement pile using the apparatus of any one of the preceding claims, the method including the steps of: driving or drilling the displacement head into the ground to displace ground material outwardly and form a bore in which a displacement pile can be formed, and selectively operating the conveying mechanism to convey ground material from outside the aperture upwardly inside the displacement head. A method as claimed in Claim 14 wherein the method includes the additional steps of gradually withdrawing the displacement head from the ground, and pumping cementitious material into the bore formed by the head.

16. A method as claimed in Claim 14 or Claim 15 wherein the conveying mechanism is an auger within the displacement head and the step of operating the conveying mechanism includes holding the auger stationary while rotating the displacement head therearound. oleo

17. A method as claimed in Claim 14 or Claim 15 wherein the conveying mechanism is an auger within the displacement head and the step of operating 25 the conveying mechanism includes rotating the auger relative to the displacement Sohead.

18. Apparatus for forming a partial displacement pile, comprising a soil displacement head adapted to be drilled or driven into the ground to form a bore in the ground by displacing ground material outwardly, the displacement head having an aperture therein and a selectively operable internal conveying mechanism for conveying ground material from outside the aperture upwardly through the displacement head, so that the displacement head may travel through the ground with less outward displacement of the ground material, and the displacement head having a passage therethrough to permit cementitious material to be passed through the displacement head into the bore as the head is withdrawn from the bore.

19. A pile when formed by the method of any one of claims 14 to 17, or claim

22. A variable displacement pile comprising a concrete column formed in the ground and having displacement pile characteristics along part of its length and non-displacement pile characteristics along the remainder of its length, the pile being formed by the apparatus of any one of claims 1 to 13, or claim 18. 21. Apparatus substantially as described herein with reference to Figs. 2 to 7 of the attached drawings. 22. A method substantially as described herein with reference to Figs. 2 to 7 of the attached drawings. DATED this twelfth day of October 2005 JOHN WAGSTAFF CONSTRUCTIONS PTY LTD By their Patent Attorneys Cullen Co. 0 0 0 0 0• 0 0 o