GB2400880A

GB2400880A - Former for use in removing the tops of piles

Info

Publication number: GB2400880A
Application number: GB0408883A
Authority: GB
Inventors: Alastair Seaton
Original assignee: Cordek Ltd
Current assignee: Cordek Ltd
Priority date: 2003-04-22
Filing date: 2004-04-21
Publication date: 2004-10-27
Also published as: GB0408883D0

Abstract

A former (5) for use in casting an elongate concrete pile has a cross- section generally corresponding to the cross-section of the pile to be cast. An access hole (8) extends through the thickness of a middle portion of the former (5) and a number of holes of smaller cross-section (9, fig 2) accommodate the reinforcing bars (3) of a pile cage. The concrete is cast to a level above the former (5) and the former (5) is then broken up so that the portion of concrete can be easily removed. The former (5) may be made from plastic such as polypropylene or expanded polystyrene.

Description

Former for use in Casting of Piles

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This invention relates to a former for use in casting a pile and to a method of casting a pile.

In a known method of casting a pile, a reinforcement cage is placed in a cylindrical elongate hole that has been formed in the ground and concrete is pumped into the hole using a dispensing device that is lowered into the hole and raised as the level of concrete rises. Commonly some water will have collected in the bottom of the hole and that is displaced by the concrete so that the uppermost portion of the cast pile is not of the optimum composition. It is then necessary to break off the uppermost portion of the pile so that the whole remaining length of pile is of the optimum composition and consequently of the required structural strength. The procedure of breaking off the uppermost portion of the pile is time consuming, especially when the pile is of relatively large diameter.

According to the invention there is provided a former suitable for use in casting a pile, the former being generally of a ring shape with an access hole extending axially through a middle portion thereof and a plurality of holes of smaller cross-section than the access hole extending parallel to the axial direction for accommodating upright members of a reinforcement cage of the pile.

A former of the kind just described can be placed immediately above the final level of pile required. When the pile is cast, concrete can be pumped into the hole in the ground as in the known method with the dispensing device being lowered through the access hole in the former.

Casting is continued until material is present both in the access hole of the former and in the region above the former. The material at or above the level of the former can then be removed relatively easily and the concrete in the access hole of the former, that portion of the concrete being of much smaller cross-sectional area than the cross- sectional area of the pile. Preferably the material of the former is a material that is able to be broken up after casting of the pile, although it is possible to have a former that can easily be cut up or removed in some other way if preferred.

Usually piles are of circular cross-section and the former is therefore preferably of circular cylindrical shape. In other cases, however, if the pile is for example of rectangular shape (for example, if the pile is actually forming a part or all of a diaphragm wall), the former may be of other shapes, for example of rectangular cross section. In the case where the former is of circular cylindrical shape, the end faces of the former are preferably substantially perpendicular to the longitudinal axis of the cylindrically shaped former. Consequently, the access hole is disposed along the central longitudinal axis of the cylindrically shaped former. The holes of smaller cross-section are preferably angularly spaced around a peripheral portion of the former and may be equi- angularly spaced at equal radial distances from the central - 3 longitudinal axis of the former. The smaller holes are arranged according to the positions of the longitudinally extending members of the reinforcement cage and ultimately the sizes and positions of those members determine the sizes and positions of the smaller holes.

The access hole may be of any desired cross-sectional shape and may for convenience be of circular cross-section.

The dimensions of the former are preferably selected according to the size of pile being cast. Preferably, for a circular pile, the former is of circular cross-section with a diameter equal to the diameter of the pile. The pile diameter may be between 0.5 m and 2.5 m. The depth of the former may depend upon various factors and is typically in the range of 40 to 1000 mm and preferably in the range of 40 to 500 mm. Where part or all of a diaphragm wall is being formed, the former may be of generally rectangular shape and may have a length in the range of 1 m to 10 m and a width in the range of 0.2 m to 2 m. In the case of a relatively large former, it may be desirable to provide more than one access hole in the former to allow dispensing of concrete through more than one hole. The access hole should be sufficiently large to allow passage of the dispensing device used when casting the pile and may therefore have a cross-sectional area greater than 20,000 mm2, but is preferably not significantly larger than required, so as to reduce the cross-sectional area of the concrete that needs to be broken after casting of the pile.

The access hole may be tapered with the wider portion of

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the hole at the top and the narrower portion at the bottom.

The angle of the taper may be of the order of 45 degrees.

Whilst it is possible for the former to have a hollow structure it is preferably of generally solid form. The former is also preferably formed at least partly of expanded plastics material, preferably expanded polystyrene. Alternatively a non-expanded plastics material may be provided. The non-expanded plastics material may comprise a thermoplastics material such as polypropylene, or an elastomer, for example a natural or synthetic rubber. Other materials may also be used. For example, wood is commonly used as a former.

The former may be formed entirely of one material or a different material may be provided at one, for example the bottom, or at each of the opposite ends of the former. The different material may be a non-expanded plastics material and may comprise polypropylene, for example the material sold under the Registered Trade Mark CORREX.

The present invention further provides a former for use in casting an elongate concrete member, the former having a cross-section generally corresponding to the cross-section of the concrete member to be cast, an access hole extending through the thickness of a middle portion of the member and a plurality of holes of smaller coss section than the access holes extending through the thickness of the member for accommodating longitudinal members of a reinforcement cage of the elongate concrete member. The former may include any of the further features defined above or below in respect of a former according to the invention.

The present invention still further provides a former for use in casting an elongate concrete member, the former being of generally rectangular cross-section and having one or more access holes extending through the thickness of a middle portion of the member, and a plurality of holes of smaller cross-section than the access hole extending through the thickness of the member for accommodating longitudinal members of a reinforcement cage of the elongate concrete member. The former may include any of the further features defined above in respect of a former according to the invention apart from features directed to a former of circular cross-section.

The present invention also provides a cast pile including a former as defined above disposed in an upper region of the pile, there being cast material above and below the former and contained within the access hole of the former and there being upright members of a reinforcement cage of the pile passing through the plurality of holes of smaller cross-section than the access hole.

The present invention still further provides a method of casting an elongate member comprising the steps of: providing an elongate reinforcement cage, placing a former generally of a ring shape in an upper region of the reinforcement cage, the former including an access hole extending axially through a middle portion of - 6 - the former and a plurality of holes of smaller cross section than the access hole extending longitudinally and accommodating longitudinally extending members of the reinforcement cage, casting the elongate member using a dispensing device that is lowered through the access hole of the former for casting a lower region of the pile and is raised back through the access hole as the casting progresses until cast material extends up through the access hole and over the top of the former, and removing the former, the cast material in the access hole thereof and the material cast on top of the former.

It should be understood that the steps referred to may be carried out in various sequences. In particular the former may be positioned on the reinforcement cage before or after the reinforcement cage is put in position and indeed the former may be assembled as a part of the reinforcement cage while the cage is being assembled.

The former may be of any of the forms defined above.

Thus, for example, the former may be removed by breaking up the material from which it is made.

The present invention still further provides an elongate member formed by a method as defined above.

By way of example embodiments of the invention will now be described with reference to the accompanying drawings of which: Figure 1 is a sectional view of a pile which has been cast with a former incorporated in an upper - 7 region of the pile; Figure 2 is a plan view of the former; and Figure 3 is a sectional view of the former along the lines III-III marked in Figure 2.

Fig. 1 shows a vertical elongate hole 1 of substantially circular crosssection formed by an auger and in which a reinforcement cage consisting of longitudinally extending members 3 and circumferentially extending members 4 is placed, prior to pouring concrete into the hole to form a pile. The arrangement as described immediately above is conventional. In accordance with the present invention there is also provided, in an upper region of the reinforcement cage, a former 5.

Referring also to Figs. 2 and 3, the former 5 is of circular cylindrical shape and is of a sandwich construction comprising end faces formed by sheets 6 of polypropylene and a middle portion 7 formed of expanded polystyrene. The sheets 6 of polypropylene are bonded to the polystyrene middle portion 7 by adhesive. The former 5 has an access hole 8 of circular cross-section and disposed coaxially with the longitudinal axis of the pile. Ten smaller holes 9 are provided, equiangularly spaced in a circle around the access hole 3. The small holes 9 are positioned and sized to accommodate the longitudinally extending members 3 of the reinforcement cage.

In use, before any concrete is poured, the former 5 and the reinforcement cage are positioned as shown in Fig. 1. The bottom of the former 5 is placed at a level, - 8 marked L in Fig. 1, at which the top of the finally formed pile is required to be situated. The longitudinally extending members 3 are each received within respective ones of the small holes 9. In this respect it may be noted that although, for the sake of clarity, only two longitudinally extending members 2 are shown in Fig. 1, there are in fact ten such members. Concrete is then pumped into the hole 1 using a conventional dispensing device such as a tremie pipe (not shown) that is lowered into the hole through the access hole 8. As the concrete fills the hole the dispensing device is raised. Eventually the dispensing device is raised back through the access hole 8 and concrete is pumped into the hole until it reaches the level shown in Fig. 1 at which the access hole 8 is filled with concrete and there is further concrete 10 above the former 5.

As with conventional pile casting, the top portion of the pile as cast is not of an ideal composition and in particular tends to have a high water content. As a result, the top portion of the pile has to be broken away leaving the top of the finally formed pile at the level L marked in Fig. 1. As a result of providing the former 5, this breaking away of the top of the cast pile can be achieved very simply because across most of the cross section of the pile it is only the former 5 that has to be broken away. The concrete filling the access hole 8 is also broken away but that is a relatively small cross- sectional area of unreinforced concrete. Thus it becomes a - 9 simple matter to form the final pile with its top at the level L in Fig. 1.

The dimensions of piles and the nature of the reinforcements for piles varies from one application to another, and the size and nature of the former 1 may vary correspondingly. In a typical case a pile is of a diameter of more than 600 mm, the diameter of the former is the same as that of the pile and the depth of the former is about mm. The expanded polystyrene has a density of 16 kg/m3 and the polypropylene sheets are formed of CORREX (Registered Trade Mark), are 2 mm thick and have a weight per unit area of 270 g/m2. It should be understood, however, that other dimensions and other materials may be employed. For example, in another embodiment expanded polystyrene having a density of 35 kg/m3 is employed. Those skilled in the art will be well aware of alternative materials commonly employed as farmers. The former may, for example, be provided with one or more recesses in its periphery to accommodate lifting chains that are commonly connected to a reinforcement structure to enable it to be lowered into place. More particularly, a pair of diametrically opposite longitudinal grooves of rectangular cross-section may be provided in the periphery of the former for this purpose.

Figs. 4A and 4B show an example of a former 40 that is of a different shape to suit casting of a concrete member of rectangular configuration. As will be understood, the end function of the concrete member is not of particular - 10 significance to the invention and may be, for example, to form a pile of rectangular cross-section or to form a diaphragm wall. It will be seen that the former 40 of Figs. 4A and 4B has an access hole 41 (corresponding to the access hole 8 of the former of Figs. 2 and 3) and is thus still generally ring shaped. The former 40 is made of expanded polystyrene and is of a generally rectangular panel shape with a plurality of small holes 43 (corresponding to the holes 9 of the former of Figs. 2 and 3) around the periphery of the former and, more particularly, along the longitudinal side edges of the former. Although not shown in Figs. 4A and 4B, the former preferably has polypropylene sheets, preferably formed of CORREX (Registered Trade Mark) on each face, as in the case of the former of Figs. 2 and 3. The former 40 is also provided with longitudinal grooves 42 in its side edges for accommodating lifting bars that may be provided for lowering the reinforcement into position. The grooves are referred to as longitudinal since they extend parallel to the longitudinal axis of the elongate concrete member that is being formed.

The particular example of former shown in Figs. 4A and 4B is also provided with shaped end portions. More particularly, it has a male end portion 44 and a correspondingly shaped female portion 45. That is of particular value when a series of similar farmers are employed together to form a diaphragm wall.

The former 40 shown in Figs. 4A and 4B will typically - 11 have a thickness in the range of 50 mm to 1000 mm, a width in the range of 0.4 m to 2 m and a length in the range of 2 m to 10 m. In the case of a relatively long former, two or even more access holes 41 may be provided.

The former 40 is used in a similar way to the former of Figs. 2 and 3. Thus the reinforcement cage is assembled with the former 40 at the level of what will be the top of the finally formed concrete member, the cage with the former 40 is then lowered into position, concrete is pumped into the elongate space to the filled with the dispensing device (tremie pipe) initially passing through the access hole 41. Pouring of concrete continues until the concrete is well above the former 40. Once the concrete has set, the portion of the concrete above the bottom of the former 40 and the former itself is broken away, that being achieved simply by breaking away the concrete in the access hole 41.

Whilst certain particular embodiments of the invention have been described, it should be understood that many modifications may be made to suit particular applications.

By way of example, it may be convenient to form the small holes 9, 43 larger than the reinforcement that they are to accommodate and then to use an expanding foam to fill the holes. It is also possible to assemble the former from a plurality of separate pieces. For example, the former of Figs. 1 to 3 may be formed as 4 separate segments each extending around one quarter of the cylindrical former. - 12

Claims

Claims: 1. A former suitable for use in casting a pile, the former being

generally of a ring shape with an access hole extending axially through a middle portion thereof and a plurality of holes of smaller cross-section than the access hole extending parallel to the axial direction for accommodating upright members of a reinforcement cage of the pile.
2. A former according to claim 1, of substantially circular cylindrical shape.
3. A former according to claim 2, in which the end faces of the former are substantially perpendicular to the longitudinal axis of the cylindrically shaped former.
4. A former according to claim 2 or 3, in which the access hole is disposed along the central longitudinal axis of the cylindrically shaped former.
5. A former according to claim 1, in which the former is of generally rectangular cross-section.
6. A former according to any preceding claim, in which the holes of smaller cross-section are angularly spaced around a peripheral portion of the former.
7. A former according to any preceding claim, in which the access hole is of circular cross-section.
8. A former according to any preceding claim, in which the access hole has a cross-sectional area greater than 20,000 mm2
9. A former according to any preceding claim, in which the thickness of the former is in the range of 40 to - 13 500 mm.
10. A former according to any preceding claim, in which the former is formed at least partly of a plastics material.
11. A former according to claim 10, in which the plastics material is expanded polystyrene.
12. A former according to claim 10 or 11, in which a non- expanded plastics material is provided at each of the opposite ends of the former.
13. A former according to claim 12, in which the non- expanded plastics material comprises polypropylene.
14. A former according to any preceding claim, the former being made of a material that is able to be broken up after casting of the pile.
15. A former for use in casting a pile, the former befog substantially as herein described with reference to and as shown in the accompanying drawings.
16. A former for use in casting an elongate concrete member, the former having a cross-section generally corresponding to the cross-section of the concrete member to be cast, an access hole extending through the thickness of a middle portion of the member and a plurality of holes of smaller cross-section than the access hole extending through the thickness of the member for accommodating longitudinal members of a reinforcement cage of the elongate concrete member.
17. A former according to claim 16, including any of the further features specified in any of claims 1 to 15.
18. A former for use in casting an elongate concrete member, the former being of generally rectangular cross- section and having one or more access holes extending through the thickness of a middle portion of the member, and a plurality of holes of smaller cross-section than the access hole extending through the thickness of the member for accommodating longitudinal members of a reinforcement cage of the elongate concrete member.
19. A former according to claim 18, including any of the further features specified in any of claims 1 or 5 to 15.
20. A cast pile including a former according to any preceding claim disposed in an upper region of the pile, there being cast material above and below the former and contained within the access hole of the former and there being upright members of a reinforcement cage of the pile passing through the plurality of holes of smaller cross section than the access hole.
21. A method of casting an elongate member comprising the steps of: providing an elongate reinforcement cage, placing a former generally of a ring shape in an upper region of the reinforcement cage, the former including an access hole extending axially through a middle portion of the former and a plurality of holes of smaller cross section than the access hole extending longitudinally and accommodating longitudinally extending members of the reinforcement cage, casting the elongate member using a dispensing device À 15 that is lowered through the access hole of the former for casting a lower region of the pile and is raised back through the access hole as the casting progresses until cast material extends up through the access hole and over the top of the former, and removing the former, the cast material in the access hole thereof and the material cast on top of the former.
22. A method according to claim 21, in which the former is according to any one of claims 2 to 19.
23. A method of casting a pile, the method being substantially as herein described with reference to and as shown in the accompanying drawings.
24. An elongate member formed by a method according to any of claims 20 to 23.