WO2004101897A1

WO2004101897A1 - A method of constructing a pile

Info

Publication number: WO2004101897A1
Application number: PCT/IB2004/001541
Authority: WO
Inventors: Clive Wilson
Original assignee: Pass, Jonathan, Charles
Priority date: 2003-05-15
Filing date: 2004-05-13
Publication date: 2004-11-25
Also published as: EP1625258A1; ZA200510247B

Abstract

This invention relates to a method of constructing a pile. The method includes forming a shaft in the ground and then forming a helical thread in the ground around the shaft by means of a ground tapping tool. Reinforcement is suitably placed in the shaft and a liquid pile forming material, such as concrete or a cementitious grout, is introduced into the shaft for filling the pile cavity including the shaft and the helical thread. The pile forming material then is permitted to set to form the pile.

Description

A METHOD OF CONSTRUCTING A PILE

THIS INVENTION relates to a method of constructing a pile.

Reference will herein be made to a thread. Any such reference must be interpreted as a reference to a thread of the general nature of a screw thread, i.e. a helical thread.

Reference will herein be made also to a pile, a ground anchor, a liquid pile forming material, a screwpile, and a tapping tool.

A pile is a vertical or steeply inclined, elongate, structural element, located beneath the ground surface, designed to resist forces imparted on to it by structures or by zones within the ground.

A ground anchor is a horizontal, or vertical, or moderately inclined, elongate, structural element located in the ground, designed to resist tensile forces imparted onto it by structures or by zones within the ground.

A liquid pile forming material, as referred to herein, is a liquid material of a type which can be placed in a pile cavity in the ground, which hardens to form a solid pile, typically a material such as concrete or cementitious grout. A screwpile, as referred to herein, is a pile or a ground anchor that includes a central shaft and a thread formation around the central shaft.

A tapping tool, as referred to herein, is a tool which includes a helical outer blade operatively driven by a drive shaft and which can be used to form a helical thread in the ground. The leading end of such a tapping tool is the leading or deepest end during screwing in of the tool into the ground, and the trailing end is the opposite end thereof.

At least some known methods of constructing screwpiles cause substantial disturbance of ground around pile cavities, which reduces the stability of the ground. Also, in at least some known methods, substantial torque and thrust is required to drive a tapping tool screw-fashion into the ground. The current invention aims to at least ameliorate these problems.

According to the invention there is provided a method of constructing a screwpile including the steps of

forming a shaft in the ground;

forming a helical thread in the ground around the shaft by means of a tapping tool;

feeding a liquid pile forming material into the shaft for filling the pile cavity including the shaft and the helical thread; and

permitting the pile forming material to set.

During forming of the thread via the tapping tool, the latter may cause an increase in the cross-sectional area of the shaft. The method may include a step of, before forming of the thread, temporarily filling the shaft with a suitable liquid, such as a mixture of water and suspended clay particles (such as bentonite clay particles), and the like, along at least a part of its length, to prevent collapse of the surrounding ground. As such, forming of the thread may be performed using a tapping tool that defines a passage permitting displacement of such liquid therethrough between the leading and trailing ends of the tool.

The shaft may be formed in the ground using a continuous flight auger. For use in the method of the invention including the use of a liquid to prevent collapse of the surrounding ground, as defined, the stem of the auger may define therethrough a longitudinal passage, which has an outlet at the leading end of the stem. As such, the method may include feeding, during extraction of the augerfrom the ground, the liquid through the passage for performing the required filling of the shaft.

Alternatively, the shaft may be formed in the ground by driving an elongate ground piercing tool into the ground and then extracting it from the ground. Such a tool may be a solid or hollow elongate tool, e.g. a metal shaft. The ground piercing tool may, e.g., be driven into the ground by imparting consecutive impact loads onto it. For use in the method of the invention including the use of a liquid to prevent collapse of the surrounding ground, as defined, the ground piercing tool may define therethrough a longitudinal passage, which has an outlet at the leading end of the tool. As such, the method may include feeding, during extraction of the tool from the ground, the liquid through the passage for performing the required filling of the shaft.

The thread may be formed in the ground by suitable driving of the tapping tool comprising coordinated rotation and linear displacement thereof, in a screwing fashion, into the ground along the shaft, the rate of rotation being one revolution per linear displacement equal to the pitch of the helical blade of the tool, the method including subsequent screwing out of the tool with its helical blade maintained in the thread already formed, until it exits the ground. As such, in the case of the method of the invention including the temporary use of a liquid to prevent collapse of the surrounding ground, as defined, and the tapping tool defining a passage permitting displacement of such liquid therethrough between the leading and trailing ends of the tool, as aforesaid, screwing in of the tapping tool along the length of the shaft filled with liquid will cause such liquid to be displaced through its passage, thus filling the newly formed helical thread behind the trailing end as it is vacated by the blade of the tapping tool. Screwing out of the tapping tool along that length of the shaft will similarly cause such liquid to again be displaced through the passage, but in the opposite direction, so that the liquid simultaneously enters and fills the helical thread in the ground around the shaft as it is again vacated by the retreating blade of the tapping tool during screwing out thereof.

The tapping tool may be driven by a drive shaft defining therethrough a longitudinal passage which is in communication with the part of the pile cavity below the tapping tool while it is being screwed out of the ground. As such, feeding of pile forming material into the shaft in the ground may be performed, via the drive shaft, during screwing out of the tapping tool.

The shaft in the ground may be filled with pile forming material from its deep end along at least a part of its length before forming of the thread around the said part. As such, the thread around the filled part of the shaft may be formed by screwing into the ground along this part a tapping tool defining therethrough a passage permitting displacement of such material between the leading and trailing ends of the tool.

The shaft in the ground may be formed using a continuous flight auger with a stem defining therethrough a longitudinal passage, which has an outlet at the leading end of the stem. As such, during extraction of the auger from the ground, liquid pile forming material may be fed via the passage to perform the required filling of the shaft.

The shaft in the ground may be formed using a piercing tool defining therethrough a longitudinal passage, which has an outlet at the leading end of the tool. As such, during extraction of the tool from the ground, liquid pile forming material may be fed via the passage to perform the required filling of the shaft.

Feeding of pile forming material into the shaft may be performed after forming of the thread.

The thread in the ground may be defined by means of a tapping tool which includes a hollow central shaft and a helical blade around the shaft, the shaft defining therethrough a passage between an aperture defined at its leading end and an aperture defined through its wall at the trailing end of the helical blade.

The pile cavity may be formed by means of a piling device including a continuous flight auger and a tapping tool defining attachment formations permitting the tool to be releasibly attached to the leading end of the auger in a collinear configuration, the tapping tool defining therethrough a passage permitting displacement of a liquid pile forming material therethrough between its leading and trailing ends. As such, forming of the shaft in the ground may be performed using the continuous flight auger without the tapping tool attached thereto and, after extracting the auger from the shaft, the tapping tool may be attached to the auger for forming the thread.

The method may include placing at least one reinforcement member in the shaft formed in the ground. In use of the tapping tool, the combination of the tool and a drive shaft driving it may define therethrough a longitudinal passage and the method may include at least partially inserting the reinforcement member into the longitudinal passage in the combination before the step of forming the thread around the shaft in the ground, inserting the reinforcement member in the shaft of the pile cavity during the said step, and screwing the tapping tool out of the ground whilst leaving the reinforcement member in the shaft. The reinforcement member may be engaged with the leading end of the tapping tool via an engagement formation which, in the axial direction of the tool, permits displacement of the reinforcement member with respect to the tool only in a direction away from the drive shaft operatively driving the tool.

It is envisaged that the capacity of the completed pile to resist anticipated forces will be assured by selection of a suitable shaft size and tapping tool configuration for a particular type of ground. Also through such suitable selection, the torque required to rotate the tapping tool during screwing in thereof may be minimized.

The invention is described below by way of example with reference to and as illustrated in the accompanying diagrammatic drawings. In the drawings:

Figures 1 to 7 show a number of elevational diagrams illustrating a sequence of steps in a method of constructing a screwpile, in accordance with the invention;

Figure 8 shows a diagrammatic axial section through a tapping tool used in the method of the invention;

Figure 9 shows a diagrammatic axial section through a part of a piling device which may, alternatively, be used in the method of the invention; and

Figures 10 to 12 show a number of elevational diagrams illustrating a sequence of steps for determining ground strength as an initial step in a method of constructing a screwpile, in accordance with the invention.

The strength of the ground in which the screwpile is to be constructed may be determined by any suitable method before its design and construction. One such method is illustrated in Figures 10 to 12 and described below. The required physical properties of such a screwpile may be designed based upon the strength of the ground so determined and the intended or specified design loads. In Figure 1 , a continuous flight auger 10 is used to form a vertical shaft 12 in the ground 14. The continuous flight auger 10 has a central hollow stem 16. As such, the stem 16 defines therethrough a longitudinal passage which has an aperture 18 at the operative bottom or leading end of the stem. As will become apparent from the description below, the shaft 12 will accommodate the central shaft of the screwpile being constructed.

In Figure 2, the continuous flight auger 10 is being extracted from the shaft 12. A liquid pile forming material in the form of a cementitious grout 20 is being fed via the passage in the stem 16 and the aperture 18 into the portion of the shaft 12 below the continuous flight auger 10, thus progressively filling the shaft 12 with cementitious grout 20 as the continuous flight auger 10 is extracted.

In an alternative example of the method of the invention (not illustrated), a shaft such as the shaft 12 may be formed in the ground by driving an elongate ground piercing tool into the ground and then extracting it from the ground. Such a tool may be a solid or hollow elongate tool, e.g. a metal shaft. It may, e.g., be driven into the ground by imparting consecutive impact loads onto it. It may define therethrough a passage equivalent to that in the stem 16 of the auger 10.

In Figure 3, the continuous flight auger 10 has been completely extracted from the shaft 12 and the shaft 12 has been filled with cementitious grout 20 along a part of its length, i.e. along a length 22. A tapping tool 24 is positioned over the shaft 12 in coaxial alignment therewith.

As shown in Figure 8, the tapping tool 24 includes a hollow central shaft 26 and a thread-forming helical blade 28 around the shaft. The central shaft 26 defines therethrough a passage 30 between an aperture 36 at its leading end and an aperture 38 defined through its wall 40 at the trailing end of the thread-forming blade 28. The central shaft 26 defines at its trailing or upper end a formation 42 by means of which it is removably attached to a matching internally threaded coupler 44 of a drive shaft 46. The drive shaft 46 defines therein a passage 50, which is continuous with the passage 30 of the central shaft 26. A device 48 prevents rotation of the central shaft 26 with respect to the coupler 44.

With reference again to Figure 3, steel reinforcement 54 has been inserted into the combination of the central shaft 26 and the shaft 46. An engagement formation in the form of a transverse length of steel reinforcement 56 has been attached to the bottom of the steel reinforcement 54. The length of steel reinforcement 56 abuts against the leading or bottom end of the tapping tool 24 and, as such, permits displacement of the steel reinforcement 54 with respect to the tapping tool 24 only in a direction away from the shaft 46.

In Figure 4, a thread 58 has been formed in the ground 14 around the shaft 12 along the top half of its length whilst screwing the tapping tool 24 into the shaft. The tapping tool 24 particularly is being driven by a suitable rig (not shown) which causes coordinated rotation and linear displacement of the tool, in a screwing fashion. The rate of rotation of the tool 24 is one revolution per linear displacement equal to the pitch of the helical blade of the tool.

As the tapping tool 24 is displaced through the length of the shaft 12 filled with cementitious grout 20, such grout is displaced into the aperture 36 at the leading end of the tapping tool 24, via the passage 30 (see Figure 8) defined through the tapping tool 24, via the aperture 38, and into the thread 58 in the ground above the tapping tool 24.

The level of cementitious grout 20 above the tapping tool 24 will drop in both the thread 58 in the ground as well as in the hollow drive shaft 46 as the tapping tool 24 is screwed downwards and thus causes the total volume of the pile cavity to increase due to the formation of the surrounding thread 58 in the ground. Additional cementitious grout may be fed via the shafts 46 and 26 or directly into the thread 58 at the ground surface, to completely fill the pile cavity with such grout. In an alternative implementation of the method of the invention (not illustrated), the dimensions of a tapping tool used to form a thread around a shaft in the ground may be such that the tool causes the cross-sectional area of the shaft to increase during forming of the thread.

In Figure 5, the tapping tool 24 has been screwed down to the bottom of the shaft 12 and the pile cavity, comprising the shaft 12 and the thread 58 in the ground, has been completely formed.

In Figure 6, screwing out of the tapping tool 24 is being performed. During such screwing out, cementitious grout 20 within the thread 58 in the ground above the tapping tool 24 is displaced into the aperture 38, thence through the passage 30 (see Figure 8), the aperture 36, and into the portion of the shaft 12 below the tapping tool. Low pressure is induced in the liquid in the part of the thread 58 in the ground being vacated by the thread-forming blade 28 as the tapping tool 24 simultaneously rotates and retreats. Grout 20 is thus urged into that part of the thread 58 in the ground, thereby filling it and maintaining its shape and dimensions in opposition to pressure within the surrounding ground that might otherwise collapse it. The steel reinforcement 54 remains in the shaft 12 as the tapping tool retreats upwards, due to viscous resistance by the cementitious grout 20 and the effect of gravity on the steel reinforcement.

In Figure 7, screwing out of the tapping tool 24 has been completed and the entire pile cavity has been filled with cementitious grout 20. Once such grout has set and cured, construction of the screwpile 59 is complete. The shaft 12 now accommodates the central shaft of the screwpile 59 whereas the thread 58 in the ground accommodates the thread of the screwpile.

As an alternative to partially filling the shaft with cementitious grout prior to forming the thread around the shaft, as in this example, the thread may instead be formed around an empty shaft which is subsequently filled with cementitious grout, liquid concrete, or other pile forming material. Alternatively, particularly where ground conditions are such that an empty shaft will not remain open if it is not supported, a shaft may be temporarily filled with a suitable liquid, such as bentonite clay slurry (comprised of such clay particles suspended in water), to provide internal support by virtue of its hydraulic pressure. At a suitable stage in the method, such slurry would be displaced from the pile cavity.

In the case of the central shaft being formed using a continuous flight auger which has a hollow central shaft which defines an aperture at its operative bottom end, as in the example of the method illustrated in Figures 1 to 7, bentonite clay slurry may be progressively fed into the portion of the shaft below the continuous flight auger during its extraction from the shaft, in a similar fashion to the partial filling of a shaft with cementitious grout as shown in Figure 2. In similar fashion to the steps shown in Figures 3 and 4 with respect to a shaft partially filled with cementitious grout, a screw thread may then be formed around the central shaft filled with bentonite clay slurry. After removal of the tapping tool from the threaded pile cavity so defined, cementitious grout or liquid concrete may be fed into the pile cavity via a delivery tube that discharges at the bottom of the cavity, to displace the bentonite clay slurry upwards and thus fill the entire cavity with cementitious grout or liquid concrete.

Such filling of a pile cavity with cementitious grout or liquid concrete, simultaneous with displacing any such bentonite clay slurry, after a thread has been formed in the ground and the tapping tool has been retracted to the ground surface, would be one of the possible instances of the method of the invention.

Filling of a pile cavity with cementitious grout or liquid concrete, simultaneous with displacing any such bentonite clay slurry when the tapping tool reaches the bottom of the pile cavity, would be another instance of the method of the invention.

Prior to, during, or after such filling with cementitious grout or liquid concrete, at least one reinforcement member may be placed in the shaft. In Figure 9, a piling device is designated generally by the reference numeral 60. It comprises a continuous flight auger 62 and a tapping tool 64. The tapping tool 64 is identical to the tapping tool 24 of Figure 8. Identical or similar features, where designated, are thus designated again by the same reference numerals as before and a description of these features may be found in the description above of Figure 8. The tapping tool 64 permits displacement of a liquid pile forming material therethrough via a passage 30 extending between two apertures 36 and 38.

The continuous flight auger 62 and the tapping tool 64 define attachment formations, in the form of formations 66 and 42, respectively, permitting the tapping tool 64 to be releasibly attached to the operative bottom end of the continuous flight auger 62 in a collinear configuration via an adapter 70. A formation 72 prevents rotation of the continuous flight auger 62 with respect to the adapter 70 and a device 48 similarly prevents rotation of the tapping tool 64 with respect to the adapter 70.

As such, in order to perform the method of the invention, the initial step of forming a shaft in the ground may be performed using the continuous flight auger 62 without the tapping tool 64 attached thereto. After extracting the continuous flight auger 62 from the shaft, the tapping tool 64 may be attached thereto for performing the step of forming the thread in the ground around the shaft.

The method of the invention clearly is variable. The invention thus extends also to any method incorporating the essential steps of the method described herein.

In Figure 10, a shaft 80 has been formed in the ground 82 using any suitable method. The diameter of the shaft 80, say 25mm, is much smaller than the diameter of a shaft of a screwpile to be constructed in the ground 82.

A tapping tool 84 attached to a shaft 86 has been positioned over the shaft 80 in co-axial alignment therewith by means of a small rig (not shown). In Figure 11 , the tool 84 has been screwed, by means of the rig, into the shaft 80 up to a predetermined depth, say 800mm, to form a helical thread 88 in the ground around the shaft. Rotation of the tool 84 has been halted. The resistance of the ground 90 engaged by the tapping tool 84 to axial displacement of the tool is now determined by measuring the axial force required to shear through the ground.

In Figure 12, the tool 84 has been screwed into the shaft 80 down to another predetermined depth, say 1600mm. Again, rotation of the tool 84 has been halted and the resistance of the ground 92 engaged by the tapping tool 84 to axial displacement of the tool is now determined.

The strength of the ground 82 so determined at various depths may be applied to the design of screwpiles to be constructed therein.

Claims

1. A method of constructing a screwpile including the steps of

forming a shaft in the ground;

permitting the pile forming material to set.

2. A method as claimed in Claim 1 , in which, during forming of the thread, the tapping tool causes an increase in the cross-sectional area of the shaft.

3. A method as claimed in Claim 1 or in Claim 2, which includes a step of, before forming of the thread, temporarily filling the shaft with a suitable liquid, along at least a part of its length, to prevent collapse of the surrounding ground.

4. A method as claimed in any one of the preceding claims, in which the shaft is formed in the ground using a continuous flight auger.

5. A method as claimed in Claim 4, insofar as it is dependent on Claim 3, in which the stem of the auger defines therethrough a longitudinal passage, which has an outlet at the leading end of the stem, and in which, during extraction of the auger from the ground, the liquid is fed through the passage for performing the required filling of the shaft.

6. A method as claimed in any one of Claims 1 to 3, in which the shaft is formed in the ground by driving an elongate ground piercing tool into the ground and then extracting it from the ground.

7. A method as claimed in Claim 6, insofar as it is dependent on Claim 3, in which the ground piercing tool defines therethrough a longitudinal passage, which has an outlet at the leading end of the tool, and in which, during extraction of the tool from the ground, the liquid is fed through the passage for performing the required filling of the shaft.

8. A method as claimed in any one of the preceding claims, in which the thread is formed in the ground by suitable driving of a tapping tool comprising coordinated rotation and linear displacement thereof, in a screwing fashion, into the ground along the shaft, the rate of rotation being one revolution per linear displacement equal to the pitch of the helical blade of the tool, the method including subsequent screwing out of the tool with its helical blade maintained in the thread already formed, until it exits the ground.

9. A method as claimed in Claim 8, in which the tapping tool is driven by a drive shaft defining therethrough a longitudinal passage which is in communication with the part of the pile cavity below the tapping tool while it is being screwed out of the ground, and in which feeding of pile forming material into the shaft in the ground is performed, via the drive shaft, during screwing out of the tapping tool.

10. A method as claimed in any one of the preceding claims, in which the shaft in the ground is filled with pile forming material from its deep end along at least a part of its length before forming of the thread around the said part and in which the thread around the filled part of the shaft is formed by screwing into the ground along this part a tapping tool defining therethrough a passage permitting displacement of such material between the leading and trailing ends of the tool.

11. A method as claimed in Claim 10, in which the shaft in the ground is formed using a continuous flight auger with a stem defining therethrough a longitudinal passage, which has an outlet at the leading end of the stem, and in which, during extraction of the auger from the ground, liquid pile forming material is fed via the passage to perform the required filling of the shaft.

12. A method as claimed in Claim 10, in which the shaft in the ground is formed using a piercing tool defining therethrough a longitudinal passage, which has an outlet at the leading end of the tool, and in which, during extraction of the tool from the ground, liquid pile forming material is fed via the passage to perform the required filling of the shaft.

13. A method as claimed in any one of Claims 1 to 8, in which feeding of pile forming material into the shaft is performed after forming of the thread.

14. A method as claimed in any one of the preceding claims, in which the thread in the ground is defined by means of a tapping tool which includes a hollow central shaft and a helical blade around the shaft, the shaft defining therethrough a passage between an aperture defined at its leading end and an aperture defined through its wall at the trailing end of the helical blade.

15. A method as claimed in any one of the preceding claims, in which the pile cavity is formed by means of a piling device including a continuous flight auger and a tapping tool defining attachment formations permitting the tool to be releasibly attached to the leading end of the auger in a collinear configuration, the tapping tool defining therethrough a passage permitting displacement of a liquid pile forming material therethrough between its leading and trailing ends, and in which forming of the shaft in the ground is performed using the continuous flight auger without the tapping tool attached thereto and in which, after extracting the auger from the shaft, the tapping tool is attached to the auger for forming the thread.

16. A method as claimed in any one of the preceding claims, which includes placing at least one reinforcement member in the shaft formed in the ground.

17. A method as claimed in Claim 16, in which, in use of the tapping tool, the combination of the tool and a drive shaft driving it defines therethrough a longitudinal passage and which includes at least partially inserting the reinforcement member into the longitudinal passage in the combination before the step of forming the thread around the shaft in the ground, inserting the reinforcement member in the shaft of the pile cavity during the said step, and screwing the tapping tool out of the ground whilst leaving the reinforcement member in the shaft.

18. A method as claimed in Claim 17, in which the reinforcement member is engaged with the leading end of the tapping tool via an engagement formation which, in the axial direction of the tool, permits displacement of the reinforcement member with respect to the tool only in a direction away from the drive shaft operatively driving the tool.

19. A method of constructing a pile substantially as described herein with reference to and as illustrated in the accompanying diagrammatic drawings.