GB2426777A

GB2426777A - A pile sleeve

Info

Publication number: GB2426777A
Application number: GB0511444A
Authority: GB
Inventors: Peter Dunn
Original assignee: Screwfast Foundations Ltd
Current assignee: Screwfast Foundations Ltd
Priority date: 2005-06-04
Filing date: 2005-06-04
Publication date: 2006-12-06
Anticipated expiration: 2025-06-04
Also published as: GB2426777B; GB0511444D0

Abstract

A pile sleeve (15) comprising a tubular body (10) which has a leading end (14) and a trailing end (16) is provided with a plurality of longitudinally extending, radially projecting fins (12), each of which is configured to define a pocket (13) open towards the trailing end (16) of the sleeve. The sleeve (15) is adapted for insertion into a substrate around a trailing end region of a primary pile (30) after the latter has been driven into the substrate, and the pockets (13) defined by the fins (12) may then be filled with grout or concrete. The fins (12) are preferably of V-shape in cross-section and taper in the direction of the leading end (14) of the sleeve (15).

Description

* 2426777

AILE SLEEVE

This invention concerns a pile sleeve.

Screw piles are known which are adapted to be driven into the ground by rotation to serve as supports to which above ground structures, such as street signs, telegraph poles and telecommunications masts may be secured. Such a pile typically comprises a tubular metal shaft provided with one or more helical blades near its leading end so that as the pile is rotated it penetrates the ground to the required depth.

Such piles are capable of high resistance to compression and are easily able to bear the weight of the above mentioned structures. However, structures such as masts are subject to horizontal wind forces and a high overturning moment. These forces are transmitted to the pile or piles supporting the structure and can lead to failure of the pile or piles when the soil at the side of the tubular shaft is overstressecl.

Wing piles are also known, which are adapted to be driven into the ground axially, by repeated impact from a drive hammer or the like. They typically comprise a metal shaft provided with longitudinally extending, radially projecting fins (also known as wings).

It is often more difficult to install piles of this type compared to screw piles. Greater force and power consumption are generally required and the terrain and ground conditions may present more difficulties for this installation method.

Pile sleeves are known, for example as disclosed in US3,011,597 and CA1, 297,259 which comprise a tubular body having a leading end and a trailing end, and a plurality of longitudinally extending, radially projecting fins mounted thereon. There may be three such fins and they may be equally spaced around the tubular body, although that is not always the case. Such pile sleeves are each adapted for insertion into the ground around a respective trailing end region of a primary pile after the latter has been driven into the ground.

Typically, a screw pile is driven into the ground until it is substantially completely embedded save for a short projecting guide portion at its trailing end. A pile sleeve of the aforesaid construction is then located around the guide portion of the pile and the sleeve is driven axially into the ground by application of force to its trailing end (e.g. by impact) so that the sleeve is embedded therein around the trailing end region of the pile with the fins of the sleeve extending radially into the surrounding ground.

The fins of all known pile sleeves are in the form of substantially flat plates. Some are of substantially triangular shape, having a wide root attached to the tubular body and tapering outwardly from the body.

The fins of most known pile sleeves taper in the direction of the leading end of the tubular body to facilitate insertion into the ground.

In some known pile sleeves the tubular body has a fixing plate closing off its trailing end so as to form a socket for fitting over the trailing end of the pile. Provision of a fixing plate facilitates the driving of the sleeve into the ground by providing a surface for transmission of force to the sleeve.

The known pile sleeves serve to stabilise the upper end region of each pile to which they are fitted and reduce the risk of overstressing soil around the upper region by virtue of the increased area of the fins in contact with the soil. This enhances the resistance of the piles to overturning forces.

However, if the fins are not quite straight as the pile sleeve is driven in, voids can be created in the surrounding soil, necessitating further compaction of soil adjacent the upper end of the pile. Such compaction can be quite a difficult operation to carry out owing to the presence of the fins.

An object of the present invention is to avoid this problem.

With this object in view, the invention provides a pile sleeve wherein each fin is configured to define a pocket open towards the trailing end.

When such a sleeve is driven into the ground around an upper region of a previously embedded pile, the fins automatically compress the surrounding soil outwards. This increases the strength of the ground and ensures a tight fit. The upwardly open pockets each provide a void which may subsequently be filled with grout or concrete, which further enhances the overall stability of the pile and its resistance to overturning forces.

Each fin is preferably formed of steel plate which is cut and bent and fixed to the tubular body of the sleeve, typically by welding.

Each fin is suitably configured to have a V-shape in cross section with the apex directed outwards. This has numerous advantages. It requires only a single bend to be formed during manufacture once the steel plate blank for each fin has been cut to size. It is easier to drive into the ground than a rounded shape, more effective at pushing back and compressing surrounding soil.

However modified cross-sectional shapes, for example closely resembling a V, but requiring more bends to less acute angles, or a more rounded bend or bends would also be possible. It would also be possible to form a Vsection fin by welding together two tringular pieces of steel plate. Two or more pieces could be welded together to provide any chosen configuration without any need for bending the plate.

Preferably, and for the same reason of facilitating insertion into the ground, each fin also tapers in the direction of the leading end of the tubular body of the pile sleeve.

The fins of the pile sleeve may be mounted at equi-distant spacing around the exterior of the tubular body. There may be two, three, four or more such fins. The fins may be mounted as opposing pairs of fins.

Where there are three or more such fins of V-shaped or similar crosssection the overall cross section of the pile sleeve resembles a star.

The steel plate of which the fins are formed may be thin enough to bend inwardly of the pocket formed by each fin when the pile sleeve is driven into hard ground.

As previously, there may be a fixing plate closing off the trailing end of the pile sleeve.

However, in other embodiments the tubular body of the pile sleeve may be open at its trailing end. Such an open-ended sleeve can be embedded below the trailing end of the primary pile.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a schematic perspective view showing a first embodiment of a pile sleeve of the invention mounted over an upper end of a pile in use and showing how a superstructure may be bolted on; Fig. 2 is a cross-section along line A-A in Fig. 1; Fig. 3 is a cross-section along line B-B in Fig. 1; Fig.. 4 is a plan view of a blank of steel plate for forming one of the fins of the pile sleeve in Figs. 1 to 3; Fig. 5 is a schematic perspective view showing a second embodiment of a pile sleeve of the invention mounted over an upper end of a pile in use and showing how the pile sleeve may be driven into the ground; and Fig. 6 is a similar view showing how a superstructure may subsequently be mounted above the second embodiment.

With reference to Figs. 1 to 3, a first embodiment of the pile sleeve 15 of the invention comprises a steel tube 10 onto which three external, radially projecting fins 12, also of steel are welded. The fins 12 each, taper towards a leading end 14 of the tube 10 and, they are all of substantially the same size.

Additionally, however, each fin 12 has a V-shaped transverse cross section, as is evident in Figs. 2 and 3, and defines a pocket 13 which is open towards a trailing end 16 of the tube 10.

As shown in Fig. 4, each fin 12 is produced from a blank 17 of steel plate which has been cut to a shape of an isosceles triangle and is then bent along its axis of symmetry 18. It is then welded to the exterior of the tube 10 along its opposing side edges.

The three fins 12 are fixed at equidistant locations, so the apices of the V-shaped cross sections are 120 apart. This results in a star shaped overall cross section, smaller towards the leading end 14, larger towards the trailing end 16, as shown in Figs. 2 and 3.

The diameter of the tube 10 and the size, configuration and number of fins (from a minimum of two) will be chosen to suit the ground conditions at the site of installation and the nature of the structure which is to be supported, and may vary in other embodiments.

A fixing plate 20 is welded onto the trailing end 16 of the tube 10 to close it at that end so that the sleeve 15 becomes, in effect, a socket which is open only at its leading end 14. The fixing plate 20 is provided with openings 21 whereby a superstructure 22 can be attached by means of fasteners, such as bolts. However, before the superstructure 22 is mounted, the fixing plate 20 also serves for percussive drive impact in an axial direction of the tube 10 by a drive hammer or the like (not shown) during installation of the sleeve 15.

The primary pile 30 with which the sleeve 15 in the illustrated embodiments is used, and over the trailing end region of which the sleeve 15 is designed to fit, may be a known screw pile comprising an elongate steel tube having a drilling tip (not shown) at its leading end and a helical plate (not shown) in the vicinity of the leading end to drive the tube axially into the ground as it is rotated. However, depending on the site and circumstances of installation, other configurations of primary pile such as a screw pile with multiple helical plates spaced along its length, or a wing pile which is driven axially, may be used.

In use, the primary screw pile 30 is firstly introduced into the ground in conventional manner, for example by being driven in rotation by a hydraulic torque head (not shown).

A short section at the trailing end of the pile 30 is left projecting as a guide portion.

The sleeve 15 is then placed upon the ground with its leading end 14 closely fitting around the aforesaid guide portion. The sleeve 15 is then driven into the ground by percussive force from any suitable conventional drive hammer until the fixing plate 20 abuts the top of the pile 30. The fins 12 are thus embedded in their radially projecting disposition below the surface of the ground and serve to reinforce the pile 30 against risk of shear failure in this region.

As the sleeve 15 is being driven in, the fins 12, by their shape and disposition, push back and compact the surrounding soil. The steel plate of which the fins 12 are formed will usually be thin enough to bend inwards when the sleeve 15 is driven into hard ground, as indicated by the broken line 19 in Fig. 3. This accentuates the penetrative force of the fins in these more difficult conditions.

Once the sleeve 15 is embedded, the pockets 13 may be filled with grout or concrete 40, as shown in Fig. 3, as may any void immediately above the fins 12.

After installation a superstructure 22, such as a street sign or a leg of a mast, can be bolted to the fixing plate 20 of the pile sleeve 15, as shown in Fig. 1.

As shown in Figs. 5 and 6, in another embodiment 115 of the pile sleeve of the invention the trailing end 116 may be open, i.e. not closed off by a fixing plate as in the Fig. 1 version. Such an open ended pile sleeve 115 can be driven into the ground by means of an adapter tool 34 which is cylindrical and will fit around the trailing end region of the primary pile 30. After the sleeve 115 and its fins 112 have been driven to the required depth, the adapter tool 34 is lifted off and a socket 119 with a fixing plate may be located in its place over the top of the primary pile 30. A superstructure 134 can then be bolted to the fixing plate 120.

This arrangement enables the fins 112 provided by the pile sleeve 115 to be located at varying depths relative to the primary pile 30 to suit the site specific details. For example, there may be drains in close proximity to the pile near to the surface which could be damaged by lateral thrust from the fins if they are located at the same depth, so the fins might need to be located deeper to avoid such thrusts. There may also be denser soil at a slightly lower level which, although not of sufficient strength to support the pile without fins would allow much smaller fins to be used. This may be of advantage when the available area for fms is limited, eg, between buried services.

The foregoing is illustrative and not limitative of the scope of the invention and details may vary in other embodiments. For example, the size, configuration, number and disposition of the fins may differ from the illustrated embodiments. Also, the method of installation of the inventive pile sleeve is not critical and can be by application of either a constant pressure or by rapid percussive force, such as by a pneumatic or hydraulic hanirner.

Claims

1. A pile sleeve comprising a tubular body which has a leading end and a trailing end, which is provided with a plurality of longitudinally extending, radially projecting fins, and which is adapted for insertion into a substrate around a trailing end region of a primary pile after the latter has been driven into the substrate, characterised in that each fin is configured to define a pocket open towards the trailing end of the sleeve.

2. A pile sleeve as claimed in claim 1 wherein the fins are of V shape in cross section.

3. A pile sleeve as claimed in claim 1 or 2 wherein the fins taper in the direction of the leading end.

4. A pile sleeve as claimed in claim 1 or 2 wherein the fins are mounted at equi- distant spacing around the exterior of the tubular body.

5. A pile sleeve as claimed in any preceding claim wherein three fins of substantially equal size are provided.

6. A pile sleeve as claimed in any preceding claim wherein the body has a fixing plate across its trailing end.

7. A method of introducing a pile and sleeve assembly into the ground comprising the steps of driving the pile into the ground until it is substantially completely embedded save for a short projecting guide portion at its trailing end, providing a pile sleeve comprising a tubular body having a leading end and a trailing end and also having a plurality of longitudinally extending, radially projecting fins, each configured to define a pocket open towards the trailing end, locating the leading end of the sleeve around the guide portion of the pile and driving the sleeve axially into the ground by application of force to its trailing end so that the sleeve is embedded therein around a trailing end region of the pile with the fins extending radially into the surrounding ground.

8. A method according to claim 7 including a further step of filling the pockets defined by the fins with grout or concrete.

9. A pile sleeve substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.