GB2261456A - A shoe for a concrete pile - Google Patents

Abstract

A concrete pile (20) having a body formed from a pre-stressed concrete pipe or tube (21) is fitted with a pile shoe having a metal shutter (25) welded to a support ring (22) of the tube. The shutter and the interior of the tube adjacent the shutter are filled with concrete or grout. In a preferred embodiment the shutter has a central rod which extends preferably axially of the pile. In a further embodiment a reinforcement cage (28) is provided in the end of the tube to support the end of the pile. The pile is filled with concrete or grout (29) to at least cover the reinforcement cage to form a solid pile shoe. The fill helps to transmit the forces on the shutter evenly to the pile with the aid of the central rod and the cage (28). <IMAGE>

Description

CONCRETE PILE This invention relates to piles for use in the construct ion industry and in particular to a pre-stressed concrete pile.

A pile is a pipe or rod rammed into the ground by means of a pile driver to support the foundations of a superstructure.

In the past four different types of piles have been used; timber piles, steel piles, reinforced concrete piles and pre-stressed hollow concrete piles. Each type has its uses and generally the later types were developed to overcome the disadvantages of the early types. For example, the steel pile is superior to timber piles in most situations.

The concrete pile may be either cast or precast. The cast in situ method involves a use of hollow steel shaft being driven into the ground, being filled with concrete and removed before the concrete sets. Sometimes the steel shafts are removed before the concrete was poured. This involves double handling of the steel shafts but is cheaper than leaving the steel shaft in the ground.

Precast concrete piles would have a cast iron pile shoe cast into the point of the pile. However, these piles were difficult to handle and transport as they should be a single length to provide the necessary strength which means that they were often 30 meters long. This leads to considerable handling difficulties.

Pre-stressed concrete piles are formed from spun concrete pipe and come in lengths of 12 meters. This has considerable handling advantages. The pre-stressed piles have metal rings formed at the ends of the pile. These are normally cast into the pipe when the pipe is being formed.

These rings allow the length of the pile to be increased by welding together the rings of adjacent pile sections. The pre-stressed nature of the concrete in these piles allows the sections to be welded together while preserving the strength of the pile.

The prestressed concrete pile or hollow concrete pile, although made from pre-stressed high strength spun concrete, has low tensile strength. Hence, the point or lower end of the pile is closed by means of a metal shutter or shoe to prevent soil from entering the hollow section of the pile. The hollow section is used to increase the compressive stress on the concrete. If the point was not closed, the soil would fill the lower portion of the pile and burst the pile.

Two typical shutter types are shown in Figures 1 and 2.

Figure 1 illustrates, in cross section, a shutter known as a conical or hollow shoe. This conical shoe is made of metal and fits over the end of the pile to divide the ground as the pile is driven into place.

Figures 2a and 2b illustrate a shutter known as a "cross shoe" comprising a metal plate placed across the end of the pile and having a metal cross welded to the face of the plate to give it strength. The cross also acts as a point to help divide the ground as the pile is driven into place.

In soil of a soft nature, such as clay, this arrangement works satisfactorily. However, in soil which is of a hard nature or which contains hard stones or boulders e.g.

gravelly sand or cobalt, the shutter is often damaged allowing soil to enter the pipe and often leading to damage or failure of the lower portion of the pile by horizontal bursting or fracture around the metal/concrete interface.

The strength of the conical shoe does not match the strength of the concrete pipe and may be damaged by boulders, hard ground etc. and pushed into the hollow interior of the pile. Also the hollow conical shoe may fail after the superstructure has been built due to metal fatigue or whatever, causing an unplanned settling or shifting of the foundations.

The cross shoe does have the strength to stop material entering the hollow pile shaft but .i it creates bursting tensile forces in the concrete directly above each end of the cross as the ends of the cross are acting in a similar fashion to an anchor plate in post-tensioning concrete when the pile is being driven. Hence, it has been found that the concrete pile may fail due to reduced area of concrete section caused by tensile splitting force of the pile base during percussion driving. The concrete pile disintegrates at its pile tip in sub-soil in which the material is harder than the concrete of the pile.

More recently, a "steel composite pipe pile" has been developed to overcome hard ground problems. This construction is expensive although not as expensive as all steel piles. The hollow concrete pile is formed within a steel jacket.

Therefore, there is a need for a pile shoe which is more evenly matched in strength to the concrete pile, which can be successfully used in hard soil conditions and which is economical to produce and for a pile which can be used in hard soil conditions.

Accordingly, in one aspect thereof, the present invention provides a shoe for a prestressed or partial prestressed concrete pile comprising a metal shutter, and a rod connected to the metal shutter and arranged to enter into the concrete pile.

Preferably, the metal shutter is conical in shape panda reinforcement cage is provided which is arranged to locate within the pile and extends into the interior of the metal shutter.

According to a second aspect, the present invention provides a concrete pile comprising a pre-stressed concrete tube, a metal ring formed on one end of the tube, a metal shutter connected to the metal ring and having a substantially conical form.

Preferably, the pile further comprises a reinforcement cage located substantially within the tube, and for a rod extending internally along the tube and extending substantially from the point of the shutter and into the cage if provided. The concrete fill covering the cage and/or the rod. In a preferred embodiment the rod extends through the metal shutter.

According to a further aspect, the present invention provides a partial prestressed concrete pile comprising a outer wall formed by a prestressed spun concrete tube, a core of concrete, reinforced concrete or cement sand grout, and a pile shoe.

Preferably, the pile shoe is substantially conical in shape and is welded to a metal ring cast in the end of the tube and is filled with core material.

Preferably, the pile shoe has a rod extending from the conical portion and along the interior of the tube.

Preferably, the pile further comprises a reinforcement cage located inside the tube adjacent the pile shoe and covered by the core material.

According to a further aspect, the present invention provides a method of forming a partial prestressed concrete pile comprising the steps of; taking a length of prestressed hollow spun concrete tube having metal facing rings, welding a metal pile shoe to one metal facing ring, are filling the pile shoe and the interior of the pile in the region of the pile shoe with concrete or grout fill.

Preferably, the method further comprises welding a rod to the inside of the metal pile shoe so that the rod extends into the hollow tube and/or forming a cage from reinforcing bars sized to fit inside the tube and fitting in the cage to the tube such that the cage supports the end of the tube adjacent the pile shoe and is covered by the concrete or grout fill.

Preferably, sufficient fill is added to substantially fill the tube and more preferably, reinforcing bars are inserted into the tube and extend substantially along the length of the tube.

In the basic form of the invention, the partial prestressed concrete pile has advantages over the prestressed hollow pile in that the tip or point of the pile is solid and thus can be driven through harder ground more easily with less problems. The modification to the pile shoe, which effectively reinforces the end of the pile, allows the pile to be used satisfactorily in even harder conditions.

When the pile is fully filled with concrete or grout it combines the advantages of the prestressed hollow pile and the solid cast concrete pile. The prestressed wall allows the pile to be made in manageable lengths which can be welded together without loss of strength. The prestressed wall also provides the improved lateral tension strength while the solid core of unstressed concrete, either reinforced or not depending on the application, greatly increases the load carrying capacity of the pile. Hence greater loads can be handled by the same number of pile of a similar size or the number or size of the piles used can be reduced leading to cost savings.

Preferred embodiments of the invention will now be described, by way of example, only with reference to the accompanying drawings in which: Figure 1 illustrates a prior art conical pile shoe in cross section; Figure 2a illustrates in cross section a prior art cross pile shoe; Figure 2b illustrates a plan view of the cross shoe of Figure 2a; Figure 3 is a sectional view of a pile made in accordance with the present invention; Figure 4 is sectional view of a modified pile made in accordance with the present invention; Figure 5 is a pictorial illustration in partial section of a further pile made in accordance with the present invention; Figure 6 is a sectional side view of the pile of the Figure 5 under construction; Figure 7 is a cross sectional plan view of Figure 6 taken at section A-A; Figure 8 illustrates an alternative shutter to that of Figure 6;; Figure 9 illustrates a reinforcement cage as used in the embodiment of Figure 5; Figures 10, 11 and 12 illustrate the assembly of the embodiment of Figure 5; and Figure 13 illustrates use of the pile according to the embodiment of Figure 8.

The pile shown in Figure 3 is similar in construction to the hollow pile of Figure 1. However, the pile shoe 25 and the pile 21, at least in the region of the shoe, is filled with concrete, reinforced concrete or cement sand grout fill 29. The pile is a partial prestressed concrete pile in that the pile has an outer layer of prestressed concrete, i.e. the prestressed high strength spun concrete pipe, and an inner core of unstressed concrete, reinforced concrete or grout. The fill serves two purposes. It reinforces the pile shoe and helps to transmit the driving force from the pile to the shoe and it increases the load bearing capacity of the pile compared with a standard hollow concrete pile of the same size.

A modified version of the pile tip is shown in Figure 4.

Here a central rod 30 is used to reinforce the tip of the conical pile shoe 25. This rod helps to transmit the forces between the pile shoe and the prestressed wall of the pile. The rod helps to distribute the forces between the pile shoe and the prestressed concrete wall more evenly.

In the preferred embodiment shown in Figures 5 to 7 a reinforcement cage 25 is used to reinforce the fill and to aid in the smooth transfer of forces between the tube and the pile shoe 25. The cage may be used instead of the rod 30 (Figure 5) or in addition to the rod as shown in Figure 6 which is the most preferred arrangement.

In Figure 5 the pile 20 is shown pictorialiy in partial section to show that the pile comprises a section of concrete pipe or tube 21. The tube 21 is a length of prestressed high strength spun concrete pipe. Fitted to one end is a metal facing ring or collar 22. This ring 22 has a flat section 23 which covers the face of the tube, and a skirt section 24 which extends along the surface of the tube to hold the ring in position. This ring 22 would normally be fitted to the tube when the tube is being produced but may be posted fitted.

Depending from the ring is a nose cone or conically shaped pile shutter 25. Inside the tube a reinforcement cage 2S can just be seen in ghost and the interior is shown filled with concrete or a cement sand grout 29. The infill covers the reinforcement cage 2S and fills the void in the shutter 25.

The shutter, more clearly shown in Figure 6, has a solid point or tip 26 and a skirt 27. A rod 30 extends axially of the tube and extends from the tip 26 of the shutter 25 into the cage 28. The shutter is shown formed in two parts with the skirt being welded to the tip. The skirt is also welded to the ring 22. The ring and shutter are made of steel. The rod 30 is welded directly to the tip 26.

A further facing ring 22' is shown fitted to the upper end of the tube. This is used to connect this tube to a further tube to extend the length of the pile in use (as shown, for example, in Figure 13) by welding adjacent rings together.

The reinforcement cage 28 is made of steel reinforcement bars and is sized to fit neatly within the tube 21. The cage comprises vertical members and peripheral members. In Figure 6 the peripheral members are rings while Figures 9 to 11 shown spiral peripheral members (helical binding).

Figure 7 is a sectional vie of Figure 6 taken at section A-A. It shows how the cage fits into the tube and the arrangement of the vertical members of the cage. The vertical members are turned to close the cage at the bottom. The rod 30 is shown extending axially within the tube.

An alternative shutter is shown in Figure s. The rod is again welded directly to the tip 26 but the tip is formed with a protuberance 31 which resembles a round ended shaft extending through the tip. Alternatively, the rod may extend through the shutter and effectively replace the tip such that the shutter skirt 27 is welded directly to the rod 30 with suitable reinforcement if required.

The cage of Figure 9 has an open top to allow easier filling with concrete or grout. The peripheral members are shown as a continuous spiral for drawing simplicity.

In fitting the shoe to the tube, the ring 22 is formed on or fitted to the end of the tube. The cage is inserted into the tube as shown in Figure 10. A small portion of the cage hangs from the tube to give better support to the ring and to the end of tube and to provide closer contact with the shutter through the grout or concrete fill. The shutter is then fitted by inserting the rod through the cage and into the tube. The shutter skirt 27 is welded to the ring as per Figure 11.

The shutter, cage and tube are then filled with grout or concrete as shown in Figure 12. The fill may cover just the cage and shutter or it may fill the entire tube. For certain applications, it is desirable not only to fully fill the tube with concrete fill but to add reinforcement along the entire length of the pile. In this arrangement the cage may be sufficient in length to extend fully along the tube or additional reinforcement cages may be provided.

Figure 13 illustrates a typical application of the pile.

The pile has a shutter of the extended nose type shown in Figure 8. The pile has been extended by a second pile member 40 welded to the first pile 21. Dowel bars 41 extend from the top of the pile for connection to the foundations of the superstructure.

The pile shoe may be supplied with or without the ring 22 for fitting to piles on site or the pile can be provided with the pile shoes factory fitted. Also, the filling of the pile shoe and/or- pile with fill may best be done on site for ease of handling and transporting the piles to a site. The extended nose embodiment is particularly suitable for use in hard or bouldery ground conditions.

The shutter or pile shoe is now solid and will not settle or collapse once in position. The strength of the shutter is increased by being solid and also by the central rod which transfers the force exerted on the point of the shutter more uniformly to the tube by the concrete fill and the reinforcement cage. The reinforcement cage prevents horizontal bursting and provides an increase in the lateral resistance of the pile. Thus this type of pile shoe fitted to the standard hollow concrete pile provides a solid shoe with an even transfer of forces from the shoe to the pile.

This type of pile, which may be called a partial prestressed concrete pile, improves the driving through granular material and achieves a greater load carrying capacity and lateral resistance of the pile for concrete piles of a similar diameter. The lateral resistance of the pile can be increased by providing additional reinforcing bars in the concrete core as required.

The partial prestressed concrete pile of the present invention may be made in convenient sections or lengths.

The lead pile has a pile shoe as previously described. The pile has an outer precast concrete wall and a core of unstressed cast concrete fill. The pile sect ions are joined by welding together the facing rings 22 of adjacent pile sections.

Claims (15)

Claims:

1. A shoe for a prestressed or partial prestressed concrete pile comprising: a metal shutter; and a rod connected to the metal shutter and arranged to extend into the pile.

2. A pile shoe as defined in claim 1 wherein the metal shutter is substantially conical in shape.

3. A pile shoe as defined in claim 1 or claim 2 further comprising a reinforcement cage arranged to locate within the pile adjacent the pile shoe.

4. A pile shoe as defined in claim 3 wherein the reinforcement cage extends into the interior of the metal shutter.

5. A pile shoe as defined in any one of claims 1 to 4 wherein the rod extends through the metal shutter and acts as a point for dividing the soil.

6. A shoe for a concrete pile substantially as hereinbefore described with reference to Figures 4 to 12 of the accompanying drawings.

7. A concrete pile comprising: a prestressed concrete tube; a metal shutter closing one end of the tube; and a concrete core filling the metal shutter and at least a portion of the tube adjacent the shutter.

S. A pile as defined in claim 7 wherein the interior of the tube is substantially filled with concrete or grout.

9. A pile as defined in claim 7 or 8 further comprising a reinforcement cage located substantially within the tube and adjacent the metal shutter.

10. A pile as defined in claim 7, 8 or 9 further comprising a rod extending axially of the tube and extending substantially from a point formed on the shutter and into and along the tube.

11. A pile as defined in claim 10 wherein the rod extends through the metal shutter.

12. A pile as defined in any one of claims 7 to 11 further comprising a metal ring formed on the end of the tube adjacent the shutter wherein the shutter is welded to the metal ring.

13. A partial prestressed concrete pile substantially as hereinbefore described with reference to Figures 3 to 13 of the accompanying drawings.

14. A method of preparing a partial prestressed concrete pile comprising the steps of: taking a length of prestressed hollow spun concrete tube having metal facing rings, welding a metal pile shoe to one metal facing ring, and filling the pile shoe and interior of the pile in the region of the pile shoe with concrete or grout fill.

15. A method of making a concrete pile according to any one of claims 1 to 14, substantially as herein described with reference to the drawings.

15. A method as defined in claim 14 further comprising the step of welding a rod to the inside of the metal pile shoe so that the rod extends into the hollow tube.

16. A method as defined in claim 14 or 15 further comprising the steps of forming a cage, from reinforcing bars, sized to fit inside the tube and fitting the cage to the tube such that the cage substantially lays adjacent the end of the tube to which the pile shoe is fitted, and adding sufficient fill to cover the cage.

17. A method as defined in claims 14, 15 or 16 wherein sufficient fill is added to substantially fill the tube. 18. A method as defined in claim 17 wherein reinforcing bars are inserted into the tube and extend substantially along the length of the tube.

19. A method of preparing a partial prestressed concrete pile substantially as herein before described with reference to Figures 3 to 13 of the accompanying drawings.

Amendments to the claims have been filed as follows Claims 1. A concrete pile comprising a pre-stressed concrete tube, a conical metal shutter closing one end, and a cementatious core filling inside of the tube.

2. A concrete pile according to claim 1, including a rod extending from the shutter along the inside of the tube.

3. A concrete pile according to claim 1 or 2, in which the cementatious core is formed of concrete.

4. A concrete pile according to any one of claims 1 to 3, including reinforcement bars in the core.

5. A concrete pile according to claim 4, in which the bars are arranged as a reinforcement cage.

6. A method of forming a partially prestressed concrete pile comprising forming a hollow spun concrete tube, fixing a conical metal shutter to one end of the tube, and filling inside of the tube with a cementatious mixture to form a core.

7. A method according to claim 6 including providing a rod extending from the shutter along the inside of the tube.

8. A method according to claim 6 or 7, comprising filling the inside at the one end with a concrete mixture.

9. A method according to any one of claims 6 to S, including placing reinforcing bars inside the one end of the pile before filling the one end with cementatious mixture.

10. A method according to any one claims 6 to 9, including forming the hollow spun concrete tube with a metal ring at its one end, and fixing the conical metal shutter to the metal ring.

11. A method according to any one of claims 6 to 10, including connecting one or more spun concrete tubes end to end to the other end of the first concrete tube.

12. A method according to claim 11, including completely filling some of or all the tubes with the cementatious mixture.

13. A method according to claim 12, including placing reinforcement bars extending the length of some or all of the tubes before adding the cementatious mixture.

14. A partially pre-stressed concrete pile substantially as herein described with reference to any one or more Figures 1 to 13 of the accompanying drawings.