GB2420581A

GB2420581A - A pile sleeve and a method of pile installation

Info

Publication number: GB2420581A
Application number: GB0523786A
Authority: GB
Inventors: Duncan Mcgregor
Original assignee: Screwfast Foundations Ltd
Current assignee: Screwfast Foundations Ltd
Priority date: 2004-11-26
Filing date: 2005-11-23
Publication date: 2006-05-31
Anticipated expiration: 2025-11-23
Also published as: GB2420581B; GB0523786D0; GB0426025D0

Abstract

A pile sleeve (15, 55) comprises a tubular body (C) which has a leading end (14) and a trailing end (16), which is provided with a plurality of longitudinally extending, radially projecting fins (12, 52), and which is adapted for insertion into a substrate around a trailing end region (E) of a primary pile after the latter has been driven into the substrate. The fins (12) may be triangular. However, in some embodiments the fins (52) of the pile sleeve (55) are not triangular, merely tapering in a lower region (52) and each fin has a free outer edge to which a terminal plate (54) is attached transversely. Preferably these terminal plates (54) are disposed perpendicular and fairly symmetrically so that the overall shape of each fin with plate affixed is a T-shape. The terminal plates (54) take up lateral load stresses so that the overall area (R) in which the sleeve (55) is embedded can be reduced, ie the fins (52) can be shorter in radial extent.

Description

A PILE SLEEVE AND A METHOD OF PILE INSTALLATION

This invention concerns a pile sleeve and a method of pile installation.

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 piles when the soil at the side of the tubular shaft is overstressed.

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.

An object of the invention is to reduce the risk of overstressing the soil at the side of a tubular pile, particularly a screw pile, but also possibly a wing pile, by increasing the area of the pile against the soil.

With this object in view, the invention provides 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.

The primary pile will generally be a screw pile, but in certain circumstances could be a wing pile.

According to the invention there is also provided 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, 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 (e.g. by impact) so that the sleeve is embedded therein around a trailing end region of the pile with the fins extending radially into the surrounding ground.

The fins of the pile sleeve are preferably of substantially triangular shape, having a wide root attached to the tubular body and tapering outwardly from the body.

The fins of the pile sleeve preferably taper in the direction of the leading end of the tubular body to facilitate insertion into the ground.

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. They may be mounted as opposing pairs of fins.

In some embodiments the tubular body of the pile sleeve 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 even transmission of force to the sleeve.

The tubular body of the pile sleeve may have a compression ring at its leading end to compact soil around the pile.

In other embodiments the tubular body of the pile sleeve is open at its trailing end. Such an open-ended sleeve can be embedded below the trailing end of the pile.

In yet other embodiments the fins of the pile sleeve are not triangular, merely tapering in a lower region and each fin has a free outer edge to which a terminal plate is attached transversely. Preferably these terminal plates are disposed perpendicular and fairly symmetrically so that the overall shape of each fin is a T-shape. The terminal plates take up lateral load stresses so that the overall area in which the sleeve is embedded can be reduced, ie the fins can be shorter in radial extent.

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 together with a screw pile to which it is to be fitted in use; Fig. la is a side view of the leading end of the pile screw in the direction of arrow 10 in Fig.1; Fig. 2 is a schematic, partial and partly sectional view showing the same embodiment of the pile sleeve of the invention as in Fig. 1 fitted onto the trailing end of the screw pile, with the drive means used to accomplish this in situ also being shown; Fig. 3 is a reduced scale sketch showing stages in a procedure in accordance with the invention for installation of the pile and the sleeve as in Figs. 1 and 2 as an assembly; Fig. 4 is a schematic perspective view showing a second embodiment of a pile sleeve of the invention together with a screw pile to which it is to be fitted in use; Fig. 5 is a reduced scale side view showing how several piles and sleeves, as in Fig. 4, may be installed side by side; Fig. 6 is a schematic perspective view showing a third embodiment of a pile sleeve of the invention fitted onto the trailing end of a screw pile; and Fig. 7 is a schematic cross- section of the pile sleeve shown in Fig. 6.

With reference to Figs. 1 and 2, this embodiment of the pile sleeve 15 of the invention comprises a steel tube C onto which four external, radially projecting fins 12, also of steel are welded. The fins 12 are triangular, tapering towards a leading end 14 of the tube C, and are arranged as opposed pairs, in this case at 90 intervals, around the exterior. They are all of substantially the same size.

The tube diameter and the size, shape 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 B is welded onto the trailing end 16 of the tube C to close it at that end so that the sleeve becomes, in effect, a socket which is open only at its leading end 14. The fixing plate B is provided with slots 18 whereby a top plate 20 is attached by means of fasteners, such as studs, nuts, bolts, with the possibility of lateral and level adjustment.

This is of practical importance for effective percussive drive impact in an axial direction of the tube C by a drive hammer G (Fig. 2) or the like. An anvil H (Fig.2) or other top structure A (Fig. 1) may be provided upon the top plate 20 to protect it from direct impact.

A compression ring D is provided as a circumferential flange projecting outwards at the leading end 14 of the tube C. This serves to compact soil around a primary pile E and below the fins 12 as the sleeve is driven into the ground.

The primary pile E with which the sleeve 15 in the illustrated embodiment is used, and over the trailing end region of which the sleeve 15 is designed to fit, is a known screw pile. It comprises an elongate steel tube having a drilling tip 22 at its leading end 24 and a helical plate 26 in the vicinity of the leading end 24. The tip has teeth 19 to facilitate penetration of the ground and the helical plate 26 serves to drive the tube axially into the ground as it is rotated.

Other configurations of primary pile may be used depending on the site and circumstances of installation, such as a screw pile with a different type of tip or helical plate, or with multiple helical plates spaced along its length.

hi use, with reference to the sequence denoted 1, 2, 3 in Fig. 3, but also to Fig. 2, the primary screw pile E is firstly introduced into the ground in conventional manner, for example by being driven in rotation by a hydraulic torque head 30. A short section at the trailing end of the pile E projects as a guide portion 28.

The sleeve 15 is then placed upon the ground with its leading end 14 a relatively close fit around this guide portion 28, the diameter of the sleeve 15 having been chosen so as to be only slightly greater than that of the primary pile B. The sleeve 15 is then driven into the ground by percussive force from the hammer G, impacting the anvil H as shown in stage 2 of the Fig. 3 sequence until the fixing plate B abuts the top of the pile E, as shown in stage 3 of the Fig. 3 sequence. The fins 12 are thus embedded in their radially projecting disposition below the surface of the ground and serve to reinforce the pile F against risk of shear failure in this region.

After installation the top plate 20 carrying the anvil H can be detached by releasing the fasteners for re-use with another pile sleeve.

Although not illustrated, in other embodiments of the invention the trailing end of the pile sleeve may be open, ie, not closed off by a fixing plate as in the above. Such an open ended pile sleeve is driven into the ground by means of an adapter tool which is cylindrical and will fit around the trailing end region of the pile, and which will preferably have a radial flange to press or impact upon the trailing end of the pile sleeve.

After the sleeve and its fins have been driven to the required depth, the adapter tool is lifted off.

This arrangement enables the fins provided by the pile sleeve to be located at varying depths relative to the pile 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 fins is limited, eg, between buried services.

Fig. 4 shows a modified embodiment 45 of the pile sleeve of the invention which, instead of having four fins projecting at right angles as in the previous embodiment, has only two fins 42, which are somewhat larger, or at least extend somewhat further outwards from the tube C. These fins 42 are mounted at opposite sides of the tube C, i.e. at approximately 180 to each other. In other respects, the sleeve 45 is similar to the sleeve 15, but lacks a compression ring and lacks the top plate and anvil. The pile it is used with is also similar to that used with the first embodiment and the same reference numerals are applied to corresponding parts to avoid repetition of description.

As shown in Fig. 5, it is envisaged that a row of piles E might be installed side by side, at a spacing which is less than twice the radial length of a fin 42, and the sleeves 45 may then be installed to fit over their trailing ends so that the adjacent fins 42 project generally towards each other, but actually overlap. Thus, the fins 42 provide a barrier just below the surface of the ground. This could be employed as a retaining system to hold up soil on loose embankments, such as those adjacent railway tracks or certain major roads. An elongate beam or channel 43 may then be secured to the fixing plates B of several adjacent sleeves 45 along the surface of the ground.

The purpose of the pile sleeves shown in Figs. 4 and 5 is obviously different from that in the previously described embodiments.

Figs. 6 and 7 show another embodiment 55 of the pile sleeve of the invention. This has four fins 52, extending symmetrically, at 900 to each other, from a central tube C. However, the fins 52 are not triangular. They each have a tapering lower region 52c, a reduced width upper region 52a, above a shoulder 52d, which provides an upper edge to a central region 52b.

A respective terminal plate 54 is fixed transversely to the free edge of the central region 52b of each fin 52. These plates 54 are preferably welded to the fin edges and preferably extend substantially perpendicular to their respective fins 52. Thus the fins 52 with these plates 54 affixed have a T-shaped cross section, as shown in Fig. 7. These extra plates 54, which may be termed "wings", enable the plan area of the pile sleeve to the reduced as lateral pressures on the sleeve are borne by the aforesaid wings, instead of by additional radially extending portion of the fins (see broken outlined in Fig. 6).

Thus Fig. 7 shows that the circular area R surrounding the winged pile sleeve is less than the circular area Q surrounding a pile sleeve without such wings, but providing comparable resistance, as indicated by the arrows X, against a lateral force indicated by arrow Z. Such a pile sleeve 55 is installed onto the trailing end of a previously installed screw pile E in the same manner as already described by impact in the direction of arrow Y into an annular flange 56 provided at the trailing end of the sleeve tube C. Apertures 58 provided near the top of the tube C, in the vicinity of the flange 56 allow for removal of the pile sleeve 55, if necessary.

The foregoing is illustrative and not limitative of the scope of the invention and details may vary in other embodiments. For example, the size, shape, number and disposition of the fins may differ from the illustrated embodiments. Also, the method of installation 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 rock breaker hammer similar to that mentioned in the specification description of the first embodiment above.

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.

2. A pile sleeve as claimed in claim I wherein the fins are of substantially triangular shape.

3. A pile sleeve as claimed in claim I 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 two fins of substantially equal size are provided and these are mounted to extend in opposing directions from the tubular body.

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

7. A pile sleeve as claimed in any preceding claim wherein the body has a compression ring at its leading end.

8. A pile sleeve as claimed in claim 1 wherein each fin has a free outer edge to which a terminal plate is transversely fixed.

9. A pile sleeve as claimed iii claim 8 wherein each terminal plate extends substantially perpendicularly to the fin to which it is affixed.

10. A pile sleeve as claimed in claim 8 wherein the fins with these plates affixed are T-shaped in cross section.

11. 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, 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.

12. A method of introducing plural pile and sleeve assemblies into the ground in the manner defined in claim 11, these assemblies being arranged adjacent each other with the piles at a spacing which is less than twice the radial length of a fin so that outer edge margins of at least some fins of adjacent assemblies overlap each other.

13. A pile sleeve substantially as hereinbefore described with reference to and as illustrated in Figs. 1 and 2, or in Fig. 4, or in Figs. 6 and 7 of the accompanying drawings.