WO2001020083A1

WO2001020083A1 - Drilling tool and method of installing a foundation pile

Info

Publication number: WO2001020083A1
Application number: PCT/GB2000/003459
Authority: WO
Inventors: Melvin Gerard England; Wilfred George Kenneth Fleming
Original assignee: Cementation Foundations Skanska Limited
Priority date: 1999-09-10
Filing date: 2000-09-08
Publication date: 2001-03-22
Also published as: AU7025900A; GB2354023B; GB2354023A; GB9921474D0

Abstract

A hole forming tool comprises a cylindrically shaped body (2) having a longitudinal axis and at least one aperture at the base thereof, and at least one blade (3) extending from the base of said cylindrically shaped body, this blade or blades being arranged such that, in use, it facilitates the displacement of soil in a substantially lateral direction with respect to the longitudinal axis of the body. The blade or blades extend in a direction substantially parallel to the longitudinal axis of said cylindrical body. The blade or blades may be arranged so as to extend across the diameter of said cylindrically shaped body.

Description

DRILLING TOOL AND METHOD OF INSTALLING A FOUNDATION PILE

The present invention relates to a tool for forming a hole in the ground, in particular for the installation of a concrete or grout pile.

A number of tools and methods for use in the installation of load-bearing piles or columns in the ground are known. One such method involves hammering a preformed pile into the ground in a series of steps. This method can be effective, but there is a risk of causing damage to the pile or to the ground due to the percussive nature of the non-continuous hammering force. An alternative method involves the use of a jack to install a pile or column which is made up of a number of discrete sections. A first section is pushed into the ground by the jack, which is then reset, and a second section is then welded or bonded to the top of the first section. The jack is then activated again, and the process repeated until the required depth has been reached. This method is low in efficiency since the jack needs to be retracted after completing each single stroke so that the next element of the pile can be inserted, particularly since a typical stroke length is less than 50cm.

A second known method is continuous flight auger piling, in which an auger with a continuous flight is caused to enter the ground by way of rotation. Soil is excavated by way of the auger flights before or during the time that the auger^' is withdrawn from the ground. As the auger is being withdrawn, concrete is pumped through the stem of the auger to the tip, thereby leading to the formation of a load-bearing pile or column. Such a method is described in the present applicant's U.K. patent application no. 9515652.7, the disclosure of which is incorporated into the present application by reference thereto.

A number of disadvantages can arise when using a continuous flight auger for the installation of a concrete pile. One disadvantage is that these tools experience a large degree of wear. Furthermore, due to the friction between the protruding auger flight and the soil, some tools become sufficiently hot to affect the wet concrete within the stem of the tool. In addition, due to the resistance of the flight against the bore wall which causes an additional downward force, these tools require a high torque to effect penetration.

Alternatively, as disclosed for example in

WO 95/12050, it is possible to use an auger head which does not excavate soil, but instead displaces the soil and compacts it into the surrounding ground. This has the advantage that less spoil is generated, and can lead to better maintenance of ground integrity and greater density in the vicinity of the pile installation. The disadvantage of such a tool is that the installation method is not as rapid as continuous flight auger methods and also the tool does not follow the same path during extraction as it followed during penetration; thus the material between the concrete flightings has to be remoulded and is consequently of lower strength.

According to one aspect of the present invention there is provided a hole forming tool comprising a cylindrically shaped body having a longitudinal axis and at least one aperture at the base thereof, characterised in that at least one blade extends from the base of said cylindrically shaped body, said at least one blade (s) being arranged sucii that, in use, it; facilitates the displacement of soil in a substantially lateral direction with respect to the longitudinal axis of the body.

As the tool is advanced to a greater depth, a downward crowding force (i.e. in a direction substantially along the longitudinal axis of the tool) is applied as well as forces to cause rotation. As a result of the downward force beneath the cylindrical body of the tool, there arises a conical build up of material which has been compacted to densities which are at least that of the surrounding material. However, this build up is disrupted by the rotation of the blade which causes the soil movement to be predominantly radial with respect to the axis of the tool . The geometry of the blade for a given soil type may advantageously be defined in order to provide the optimum ratio of torque to crowd forces required to achieve maximum boring efficiency.

A tool of the present invention has the particular advantage that during rotation of the blade soil builds up in front of the blade creating a material element. The shape of the material element is dependant upon the soil type and the pressures involved during penetration of the tool however the element generally completely or partially covers the side of the blade leading the rotational movement thereby providing a soil to soil interface of moving material which minimises the wear to the tool itself.

According to a second aspect of the present invention there is provided, a method of installing a load bearing pile in the ground, wherein: i) a hole forming tool, comprising a cylindrically shaped body having at least one blade extending from the base thereof, is driven into the ground by means of a combined downward crowding force and a rotational force, thereby causing lateral displacement of soil with respect to the longitudinal axis of said tool; and ii) said tool is withdrawn from the hole, whilst concrete or grout is simultaneously pumped through at least one aperture provided at the base of said cylindrically shaped body.

Vibrational motion may also be advantageously induced to aid the penetration of the tool. For example, a torsional oscillation may be superimposed on the period of rotation of the tool, such that the blade experiences a back and forth -radial movement. The frequency of the oscillatory motion may be chosen depending on the ground conditions. Alternatively or in addition, a vibrational motion may be applied in the direction of the downward crowding force, so as to generate an up and down oscillatory motion.

Concrete delivery occurs primarily during withdrawal of the tool and predominantly emerges at the base of the cylindrical section. The concrete flow may advantageously emerge through an aperture positioned substantially at the centre of the cylindrical body. The blade (s) may be positioned across the diameter of the cylindrical body, thereby concealing part of the aperture. In this case concrete will flow around the blade (s) . Alternatively, the blade.(s) itself need not be positioned across the diameter of the cylindrical body. Furthermore the blade may have an aperture positioned so as to substantially align with the aperture in the cylindrical body, to allow concrete to flow more freely out of the tool. A disposable bung or a gate mechanism may advantageously be used to cover the aperture during penetration into the ground and to allow concrete flow only when needed.

Variations in the geometry of the blade (s) may advantageously be chosen according to the ground conditions. For example the blade (s) may extend in a direction substantially parallel with the longitudinal axis of said cylindrical body and may be substantially planar in shape. Alternatively, the surface of the blade (s) need not necessarily be planar or parallel sided and their shape may be chosen in accordance with soil conditions. Furthermore, the blade (s) may extend beyond the envelope of the cylindrical body which will advantageously reduce the friction between the soil and the following cylinder.

The blade (s) may advantageously be positioned so as to assist the motion of the tool by direct contact with the moving soil and/or may be shaped such that soil is deliberately caught in front of the surface of the blade; for example the blade either side of the central longitudinal axis of the tool may be angled or concave blades may be employed which would deliberately capture additional soil when rotating clockwise to further remove the steel of the tool from the zone of abrasion.

In embodiments of the present invention where a number of blades are provided, they may be arranged in any number of ways at the base of the cylinder according to the ground conditions.

In a further embodiment, the tool head can be arranged to be sacrificial, such that the boring head element would be left behind and a new head fitted for the next pile. A key arrangement would advantageously be needed to ensure rotation of the head when it was connected to the following cylindrical drive shaft. Such an arrangement would be a particular advantage if tool wear was a significant factor.

According to a further aspect of the present invention there is provided a method of installing a load bearing tool in the ground, wherein a pre-cast element comprising a cylindrically shaped body having at least one blade extending from the base thereof, is driven into the ground by means of a combined downward crowding force and a rotational force, thereby causing lateral displacement of soil with respect to the longitudinal axis of said tool .

It is envisaged that according to a further embodiment, the cylindrical body of the tool may comprise a pre-formed element made of, for example steel or concrete. In such an arrangement, the entire tool is designed to form a pre-cast element which is sacrificial and stays in the ground. Alternatively, the cylindrical body may be substantially hollow having one or a number of blades extending from the base thereof . Such an arrangement would allow a hollow pre-cast element to be deposited in the ground wherein concrete is delivered into the central cylindrical area.

According to a further aspect of the present invention, there is provided A method of installing a load bearing tool in the ground, wherein: i) a hollow cylindrically shaped body having at least one blade extending from the base thereof, is driven into the ground by means of a combined downward crowding force and a rotational force, thereby causing lateral displacement of soil with respect to the longitudinal axis of said tool; and ii) concrete is deposited into the centre of the said hollow cylindrically shaped body

It is also envisaged that the mechanism to provide rotation and/or the vibrational motion need not be on the rig mast, but could actually be at the bottom of the cylindrical tube. This arrangement could have significant advantages since no rig mast would be needed, only a mechanism for providing the crowding force with possibly multiple hydraulic rams or a winch.

A tool of the present invention desirably installs predominantly cylindrical concrete elements in the ground, and as a consequence of the construction of the tool, the pile does not have - significant protrusions beyond the expected envelope of the pile. Furthermore, the present invention seeks to avoid using a high torque which is then converted to a downward motion, by choosing to use direct downward forces (crowd force) .

Another distinct advantage of the present invention is that since the soil is compacted into the surrounding ground, there is little or no spoil at the surface of the hole. Furthermore, there is no need to excavate the soil before concrete is pumped into the hole.

For a better understanding of the present invention, and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:

Figure 1 shows a hole- forming tool of the present invention;

Figure 2 shows the hole forming tool of figure 1 fro below,- Figure 3a shows a hole forming tool of the present invention from below having two blades which extend across the aperture for concrete delivery;

Figure 3b shows a hole forming tool of the present invention from below having two blades which do not extend over the aperture for concrete delivery;

Figure 4 shows a hole forming tool of the present invention from below, wherein the blade (s) is not positioned across the central aperture of the cylindrical body;

Figure 5 shows three further embodiments of hole forming tools of the present invention;

Figure 6a shows a further embodiment of a hole forming tool according to the present invention;

Figure 6b shows an arrangement of blades according to an embodiment of the present invention; and

Figure 7 shows a second arrangement of blades according to an embodiment of the present invention.

The hole forming tool shown in figure 1 comprises a cylindrical body 2, provided with a single blade 3 which extends from the base thereof in a longitudinal direction along the body's central axis. The surfaces 31 and 32 of the blade are substantially planar and parallel to each other. In use, the tool is subjected to both a downward crowding force and a torque to effect rotational motion. The blade 3 facilitates the radial motion of soil as the tool is rotated, thereby displacing the conical build up of material which occurs below the cylindrical body 2, as the tool experiences a downward force into the ground. The reader should appreciate that the dimensions of the blade will vary considerably and will depend upon a number of factors including soil conditions.

Due to the rotational motion of the blade, material builds up along the edge leading the rotational motion as illustrated by Figure 2. Elements of material 4 provide an interface between the moving material and the blade itself, thereby significantly reducing the wear on the tool.

Figure 3a and 3b illustrate from below two embodiments of the present invention wherein an aperture 5, delivers concrete at the base of the cylindrical body. The embodiment shown in Figure 3a comprises two blades 6 and 7, which are of equal length and which extend across the radius of the cylindrical body. These two blades may be fused together at the point at which they meet. It should be realised that one single blade which extends across the whole diameter of the cylindrical body may alternatively be used. The concrete flows around the two blades from the aperture 5, and is deposited into the hole during the withdrawal of the tool. The two blades 8 and 9 shown in Figure 3b do not extend across the whole diameter of the cylindrical body and the gap between the blades aligns with the aperture 6. This embodiment of the present has the advantage that concrete can flow more freely from the tool .

Figure 4 shows a further embodiment of the present invention in which the blades 11 and 12 are located at the base of the cylindrical body 10 and are positioned such that they do not extend across the central radius of the body. The blades of this embodiment extend beyond the envelope of the tool body and may consequently serve to reduce friction on the following cylinder . 5

In each of Figures 3a, 3b and 4, the blades (6,7; 8,9; 11,12) are positioned on a diameter of the base 10 of the cylindrical body. Alternative arrangements of the blades are also possible; for example, they may be 10 positioned on a chord or on chords of the generally circular periphery of base 10.

The embodiment shown in Figure 5a, comprises a cylindrical body 13 and a rectangular blade 14 15 extending from the base thereof, in which the surfaces of the blade are planar and substantially parallel to each other. The blade however need not be rectangular, but may be of any shape. Figure 5b shows a tool according to the present invention in which a blade 15

20 is trapezoidal such that as it extends in a substantially longitudinal direction from the base of cylindrical body 13, its cross-section becomes narrower. The blade 16 illustrated in figure 5c is wedge-shaped and has been positioned at the base of

25 body 17 such that it is angled with respect to the central axis of the cylindrical body. This arrangement encourages soil to be caught by the rotating blade, thereby creating a larger material interface element between the moving soil and the tool.

^0

The tool shown in Figure 6a, comprises two blades 18, attached to a boring head element comprising a sacrificial plate 19. In such an arrangement, the sacrificial plate is left behind and a new head fitted

35 for the next pile. The blades are shaped in a concave manner and are arranged on the plate 19 such that, due to their shape, soil may become more easily trapped within the blade envelope during rotation in the direction indicated by the arrow. It should be appreciated that forces may alternatively be applied to 5 induce rotational motion in the opposite direction.

Concrete flows through the aperture 20 from the stem of the cylindrical body 21. An embodiment of the present invention which utilises concave blades in order to capture additional material is shown from below in 10 Figure 7. During rotation material elements 24 build up in front of the blades 23 acting as a soil to soil interface between the tool and the moving material .

It is also possible, using an arrangement of 15 blades as shown in figure 6b, to assist the motion of the tool. Four blades 22 are positioned around the base of the cylindrical tool, and in use serve to aid the radial motion of the tool itself due to the flow of the moving soil as it passes by the blades. 20

25

^

35

Claims

1. A hole forming tool comprising a cylindrically shaped body having a longitudinal axis and at least one aperture at the base thereof, characterised in that at least one blade extends from the base of said cylindrically shaped body, said at least one blade(s) being arranged such that, in use, it facilitates the displacement of soil in a substantially lateral direction with respect to the longitudinal axis of the body.

2. A hole forming tool as claimed in claim 1, wherein said blade(s) extends in a direction substantially parallel to the longitudinal axis of said cylindrical body.

3. A hole forming tool as claimed in claim 1 or 2, wherein said blade(s) is arranged so as to extend across the diameter of said cylindrically shaped body.

4. A hole forming tool according to any preceding claim, wherein at least two blades extend from the base of said cylindrically shaped body.

5. A hole forming tool according to claim 8 or 9, wherein said blades are arranged such that they aid the rotational motion of the tool itself.

6. A hole forming tool according to any preceding claim, wherein the tool is such that the blade, when viewed from above in the direction of the longitudinal axis of said body does not extend beyond the projected envelope of said body.

7. A hole forming tool according to any one of claims 1 to 10, wherein the tool is such that the blade, when viewed from above in the direction of the longitudinal axis, of said body does extend beyond the projected envelope of said body.

8. A method of installing a load bearing pile in the ground, wherein: i) a hole forming tool, comprising a cylindrically shaped body having at least one blade extending from the base thereof, is driven into the ground by means of a combined downward crowding force and a rotational force, thereby causing lateral displacement of soil with respect to the longitudinal axis of said tool; and ii) said tool is withdrawn from the hole, whilst concrete or grout is simultaneously pumped through at least one aperture provided at the base of said cylindrically shaped body.

9. A method of installing a load bearing pile in the ground, wherein a precast element comprising a cylindrically shaped body having at least one blade extending from the base thereof, is driven into the ground by means of a combined downward crowding force and a rotational force, thereby causing lateral displacement of soil with respect to the longitudinal axis of said tool.

10. A method of installing a load bearing pile in the ground, wherein: i) a hollow cylindrically shaped body having at least one blade extending from the base thereof, is driven into the ground by means of a combined downward crowding force and a rotational force, thereby causing lateral displacement of soil with respect to the longitudinal axis of said tool; and ii) concrete is deposited into the centre of the said hollow cylindrically shaped body.