GB2398333A - Techniques for pile breaking - Google Patents

Abstract

A method of breaking a concrete pile (30) having a reinforcement (31) involves treating the reinforcement (31) with a debonding material (32) and inserting expandable tubes (33) within the pile (30) prior to it being cast. A fluid is supplied to the expandable tube (33) which causes it to expand and break the concrete pile (30) at a desired position. The expandable tube (33) may include a material which expands when in contact with a liquid.

Description

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TECHNIQUES FOR PILE BREAKING

The present invention relates to techniques for breaking foundation elements such as concrete/grout piles, barrettes and diaphragm walls.

Columns of concrete or grout, known as piles, are widely employed in the construction industry to provide a foundation for structures or buildings. Piles may comprise a pre-cast column, which is placed at a desired location in the ground, or may be cast in situ.

It is common for the pile to be provided with a reinforcement means in order to improve the structural strength of the concrete element so that it may resist greater lateral loads and greater vertical loads without distress. The reinforcement means is typically in the form of a mesh/cage and can comprise one or more reinforcement bars made from steel or the like. The reinforcement means generally extends substantially longitudinally along the major axis of the pile.

Likewise, nominally rectangular foundation elements, such as barrettes and diaphragm walls, also employ reinforcement means.

Usually, once a reinforced concrete element has been cast, the top of the concrete is broken away to an appropriate level partially exposing the reinforcement means which facilitates connection of the foundation element to the next element of the structure. This could be, for example, a pile cap integrating several piles or a beam spanning across a number of piles.

Furthermore, the concrete at the top of a foundation element may become contaminated by, for example, soil, water or other debris. It is therefore common practice, particularly for cast-in-situ techniques, to break down the top of the concrete element in order to remove any contaminated or low strength concrete. This ensures that the concrete at the top of the concrete element is of good quality.

Thus, during the installation of concrete or grout foundation elements, it is often necessary for the length of Che concrete or grout section to be reduced.

Since it is desirable for the reinforcement to extend beyond the foundation level and to be incorporated in the above structure, elements are usually cast or placed so that they extend by a certain amount above the level actually required. The concrete is subsequently broken down in order to expose sound concrete and an appropriate portion of the I. reinforcement means.

A number of techniques have been developed for breaking concrete or grout foundation elements involving mechanical breaking of the concrete above the required level. This is an arduous process, often having to be carried out manually using hand held drilling machines or vehicle driven crushers/nibblers which break up the concrete in the cross section. Not only is this process time consuming, it can result in damage being suffered to the pile below the required level. Mechanised systems employing crushers/nibblers can induce lateral forces which are often detrimental to the piles structural integrity and may also damage some of the steel reinforcing bars.

Furthermore, methods such as this produce substantial loose debris which has environmental implications and represents a hazard to those in the vicinity of the pile during the breaking procedure. Any debris must also be collected and disposed of. The use of mechanical hand held systems can also lead to an operator suffering from a condition known as white finger.

Existing alternative methods of breaking down the pile involve splitting the concrete by means of a double acting jack having two wedge shaped jaws. When inserted into a pre-formed drilled or cast hose, the jaws may apply sufficient force in substantially opposing directions to crack the concrete and allow the removal of the upper concrete section. As described in GB 2307504, this method requires the reinforcement bars -to be treated with an isolation material applied or fixed from the top of the bar to a point at, or near, the desired break level. It therefore relies upon typical is and well-known concrete debonding techniques to ensure that the concrete to be broken off is not adhered to the steel bars.

disadvantage of the method described in GB 2307504 is that it requires access to the side of the pile at the level at which the break is desired. In some instances, particularly when it is necessary for the finished top of the pile to be below ground, this can be difficult or even impossible.

The present invention seeks to provide an alternative method of breaking concrete or grout foundation elements which alleviates the problems associated with previously proposed mechanised techniques.

According to one aspect of an embodiment of the present invention, there is provided a method of breaking a concrete or grout element having a reinforcement means, the method comprising the steps of: i) treating the reinforcement means such that it will not substantially adhere to the surrounding concrete or grout; ii) casting one or more expandable elements within the concrete or grout at a desired level; and iii) supplying a fluid to the expandable element in order to cause the expansion thereof, wherein the pressure exerted by the expandable element on the surrounding concrete as it expands causes said concrete or grout element to break.

The term "fluid" should be interpreted as encompassing both liquid or gaseous fluids.

Concrete normally cracks at pressures of approximately 2 to 4 N/mm2.

1 According to another aspect of an embodiment of the present invention, there is provided a concrete or grout element having a reinforcement means and at least one expandable element cast therein, wherein supply of a fluid to the expandable element causes it to expand 29 and wherein at least a part of the reinforcement means is treated such that does not substantially adhere to the surrounding concrete or grout.

At least a part of the, or each, of the reinEorcement bars may advantageously be treated or provided with foam in order to that they are substantially isolated from the concrete. Other known debonding techniques may also be employed which comprise, for example, the use of a tape wrapped around the steel, the installation of a pre-formed cover to the bars, which may be similar to pipe lagging foam, or by coating the bars with a viscous material such as grease or bitumen before they are cast in the concrete. The debonding material should ideally cover the reinforcement down to at least the level at which the cut off is required.

In one embodiment, at least one of the reinforcement bars is provided with a sleeve or tube, preferably formed from solid plastic, to allow fluid to be pumped or poured down to the level of the expandable element.

This may be provided in addition, or as an alternative, to the foam.

Often, a steel loop is provided for connecting a plurality o reinforcement bars to form a reinforcing cage. This can assist with the mounting and support of the expandable element. Any circumferential steel associated with the reinforcement may be advantageously arranged JO remain below the final cut off level.

Ln some instances, the intended final cut-off level of the foundation element is not known. Furthermore, the depth of the foundation element may need to be varied after construction of the reinforcement. En order to accommodate this, it is therefore envisaged that a plurality of expandable elements may be provided at different levels within the concrete or grout element so that fluid can later be supplied to the element at the most appropriate level. It is also envisaged that the or each expandable element may be mounted on one or more frames that are preferable adjustable mounted to, or associated with, the reinforcement means. Thus, the final position of the expandable element(s) can be adjusted in the wet concrete/grout during the installation of the reinforcement means.

According to one embodiment, the or each expandable element comprises a material which swells when it comes into contact with a liquid such as water. Any material, synthetic or natural, that expands sufficiently when exposed to a fluid may be employed as the swellable material. For example, timber experiences a significant expansion when exposed to water. Furthermore, hydrotite would also be suitable for this purpose.

In accordance with this embodiment, the expandable elements may comprise one or more longitudinal strips of the swellable material. These may extend across the concrete or grout element at a level substantially coincident with the final cut-off level of the pile.

Alternatively, the expandable elements may comprise one or more circular/elliptical rings of swellable material. This is particularly appropriate if the reinforcement means comprises a cylindrical mesh or a plurality of bars arranged around an inner perimeter of the concrete element, since the expandable element can be arranged around the inside and/or outside of the reinforcement. Preferably, the strips or rings of swellable material are flexible, allowing the expandable elements to be positioned easily within the concrete or grout.

In another embodiment, the expandable element comprises a so-called flat jack. A typical flat jack includes a mild steel capsule, substantially circular in plan, with a cross-section that is initially dumb bell shaped. The dished portions are fitted with ground steel thrust plates. The jack may be inflated with liquid and the hydrostatic pressure is transmitted by the flat portions of the capsule through the thrust plates while the toroidal rim of the jack deforms to allow the flat faces to move apart. The maximum unconfined operating pressure of a flat jack is typically 150 bar (2200ps-i).

In accordance with this embodiment, the flat jack is preferably covered by a material, such as polythene, that does not substantially adhere to the surrounding concrete when cast in the foundation element. Thus, it becomes possible to remove (and re-use) the flat jack once the pile has been broken and the upper section lifted away.

In one embodiment, the expandable element comprises a flexible tube. This can be pressurized with water or hydraulic fluid until the expansion of the diameter of the tube is sufficient to effect a crack in the surrounding concrete. Suitable materials for the tube are PVC, rubber, rubber alloy, polyurethane, neoprene, butyl or other flexible material. Preferably, the ma-serial of the tube is chosen such that minimal internal pressure is required to cause the required expansion. By way of example, to break a 300mm diameter pile provided with a reinforced polyurethane tube which is arranged within the perimeter of a steel reinforcement cage of 200mm diameter, the tube having an internal diameter of 12mm, requires a pressure of lOOOpsi (IObar). These ratios can be readily scaled up to any cross-sectional area. An advantage of using a reinforced tube, is that it that it fails gradually under pressure. Thus, the tube tends to blister rather than crack or fail completely which would result in the pressure in the pipe being lost.

Alternatively or additionally, it is envisaged that the tube may be formed of, or may be loaded with, a material which swells when it comes into contact with a liquid such as water. For example, the tube may be formed or, or loaded with, hydrotite. It is envisaged that the fluid could be applied at atmospheric pressure to the tube containing or formed from the swellable material (e.g. it is poured down to the material).

Alternatively, or additionally in the case where the pressure exerted by the swellable material as it expands has not been sufficient to crack the concrete, the fluid could be supplied to the tube under pressure.

It would also be possible to (further) pressurize the fluid already supplied to the expandable element in connection with any of the embodiments discussed in the present application.

The fluid is advantageously supplied at an appropriate time to the or each expandable element by means of a fluid supply mechanism. This may comprise, for example, one or more pipes which extend from a fluid supply point, or reservoir, external to the concrete to the, or each, expandable element. When supplying fluid under pressure, for example in conjunction with the flexible tube embodiment discussed above, it is preferable for solid pipework to be employed for the fluid supply mechanism. The pipework is advantageously formed of standard steel although other metals may be used provided that the pipe can withstand the internal pressures that will arise when the pipework extends outside the concrete and is unconfined by the surrounding concrete. Connections such as Jubilee clips may also be used in order to ensure the integrity of the seal between the rigid pipe and the expandable tube.

The fluid may be pressurised using a hand held portable pump. Since the volume of fluid required is small, a single pump may be sufficient to fill and pressurize several expandable tube elements with the reservoir requiring only a single filling.

The or each expandable element is incorporated within the foundation element at one or more desired levels.

Preferably the expandable element is provided in a transverse plane perpendicular, or substantially perpendicular, to the major axis of the pile.

Alternatively, or additionally, the element may be provided in the form of a ring. Several rings of material may be provided depending on the diameter of the pile and these may by overlapping or arranged in a spiral. The use of a ring-shaped expandable element is particularly appropriate if the reinforcement is arranged in the form of a ring around an inner perimeter of the foundation element, since the element can be positioned around the inside and/or outside of the reinEc-cement. Locating the ringshaped element within the reinforcement perimeter ensures that the forces generated in the radially outward direction during expansion of the element are limited. This can Substantially prevent portions of the concrete wall from being pushed outwards to the point of tension failure. Similarly, arranging the expandable element in a spiral fashion to resemble a coiled hose, means that the majority of Corces generated by the element expansion are directed parallel to the axis of the foundation element.

It may also be beneficial to employ the use of a metal loop which is positioned around the outside of the ring-shaped expandable element. This would serve to direct the principal forces generated by the element expansion in a direction which is generally parallel to the axis of the pile.

lifting point is advantageously cast into the top of the concrete element in order to facilitate removal of the top section after breaking.

An advantage of the present invention, particularly embodiments which utilise strips of a swellable material or a flexible tube, is that it can be employed to break foundation elements of a variety of shapes, wherein the cross-section may or may not be predominantly circular. Furthermore, the element(s) need not be cast in the cross sectional plane normal to the axis of the element, but can be set at a chosen angle such that when the top is broken off the 1() remaining surface is set at an incline. Where a plurality of piles are installed to form a secant or contiguous wall, the expandable element can be readily arranged to either break down the tops of all piles at the same level, or at different levels as necessary.

A further significant advantage of the present invention is that the break in the concrete is usually very clean and consequently very little dust or debris is generated. Furthermore, the method is quiet and, 2() since the expandable element is cast within the foundation element itself, does not involve any mechanical drilling. Thus, noise pollution is minimised and operators are exposed to minimal vibration and noise. It is also possible to ensure that most of the force experienced by the concrete is -in a direction substantially parallel to the axis of the foundation element.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 illustrates a first embodiment of the present invention; Figure 2 illustrates a second embodiment of the present invention; Figure 3 illustrates a third embodiment of the present invention; Figure illustrates a flat jack employed in the third embodiment of the present invention; and Figure 5 illustrates a fourth embodiment of the present invention.

Figure 1 shows a sectional view through a concrete pile 1(). The pile is provided with seven reinforcement bars 11 arranged around an inner circumference of the pile.

Each of the bars is provided with a foam coating which extends from the top of the pile down to a level at or near the point at which the break is desired, in order to isolate the metal bars from the concrete. Two expandable elements, each in the form of a longitudinal strip of material 12, are provided. In this embodiment, the e-trips 12 comprise hydroLite, a material which expands or swells upon contact with water. Two of the reinforcement bars]] are provided with a solid plastic tube 13 which surrounds the foam and allows water to be pumped or poured from the top of the pile down to the level of the material 12. The elements 12 and the tube 13 are arranged such that water can be supplied to material itself.

In use, the concrete pile is installed in the ground at an appropriate level by means of conventional piling techniques. When it is desired to break down the top of the concrete pile, water is supplied to the expandable elements 12 by means of the tubes 13. Upon contact with water, the elements swell thereby generating a pressure on the surrounding concrete. When the pressure reaches a sufficient level, the concrete will crack and the upper section of the pile can be lifted away to expose the reinforcement bars.

Figure 2 shows an alternative embodiment of the present invention in which the expandable element comprises a ring 14. The ring-shaped expandable element 14 is locating within the reinforcement perimeter which has the advantage that the forces generated by the expanding element in the radially outward direction are limited.

Figure 3 shows a sectional view through a concrete pile 20. A flat jack 21 is cast within the pile at an appropriate level. In use the jack 21 is inflated with a pressurized fluid by means of a hand held pump 22 to thereby cause the flat thrust plates 23a and 23b shown in Figure 5 to be forced apart. The resultant pressure exerted on the surrounding concrete in a direction X causes a break 24 to form in the concrete pile 20. A purge valve 24 is also provided.

Figure 4 illustrates the flat jack 21 in more detail.

Figure 4A shows a plan view of the flat jack from above and shows the entry and exit valves 25 and 26 respectively. Figure 4B show the shape of the flat jack before pressuring and Figure 4C shows the shape of the flat jack after pressuring.

Figure 5 illustrates a concrete pile 30 having a plurality of steel reinforcing bars 31 disposed around an inner circumference of the pile. For illustrational purposes, the top of the concrete pile is shown already broken away to expose the intended upper surface of the pile 36. Each of the steel bars are provided with a debondinq material sleeve 32 so as to prevent the steel bars from adhering to the concrete of the pile. A flexible reinforced polyurethane tube 33 forms the expandable element of this embodiment which, in use, is connected to a pair of hydraulic feed pipes 34 which are formed of steel. Reinforced polyurcChane can advantageously sustain pressure overloading when contained by surrounding concrete. Wherl it ruptures, blistering of the tube occurs thus ensuring that immediate failure of the tube does not occur upon creation of a crack in the surrounding concrete.

Various modifications of the described embodiments are envisaged without departing from the scope of the present invention.

1. A method of breaking a concrete or grout element having a reinforcement means, the method comprising the steps of: i) treating the reinforcement means such that it will not substantially adhere to the surrounding concrete or grout; ii) casting one or more expandable elements within the concrete or grout at a desired level) and iii) supplying a fluid to the expandable element in order to cause the expansion thereof, wherein the pressure exerted by the expandable element on the surrounding concrete as it expands causes said concrete or grout element to break.

2. A method as claimed in claim 1, wherein the or each expandable element comprises a material which swells upon contact with a liquid.

3. A method as claimed in claim 2, wherein the material comprises hydrotite.

4. A method as claimed in claim 1, wherein the or each expandable element comprises a flat jack.

5. A method as claimed in claim 1, wherein the or each expandable element comprises a flexible tube.

6. A method as claimed in claim 5, wherein the flexible tube comprises, or contains, a material which swells upon contact with a liquid.

7. A method as claimed in claim 6, wherein the material comprises hydrotite.

8. A method as claimed in any preceding claim, wherein the reinforcement comprises a cage or mesh.

9. A method as claimed in any one of claims 1 to 3, wherein the reinforcement means comprises longitudinal bars.

10. A method as claimed in any preceding claim, wherein the fluid is supplied to the expandable element under pressure or wherein the fluid already supplied to the expandable element is (further) pressurized.

11. A concrete or grout element having a reinforcement means and at least one expandable element cast therein, l5 wherein supply of a fluid to the expandable element causes it to expand and wherein at least a part of the reinforcement means is treated such that does not substantially adhere to the surrounding concrete or grout.

12. A concrete or grout element as claimed in claim 11, wherein the or each expandable element comprises a material which swells upon contact with a liquid.

13. A concrete or grout element as claimed in claim 12, wherein the material comprises hydrotite.

14. A concrete or grout element as claimed in claim 11, wherein the or each expandable element comprises a flat jack.

15. A concrete or grout element as claimed in claim 11, wherein the or each expandable element comprises a substantially flexible tube.

16. A concrete or grout element as claimed in claim 15, wherein the flexible tube comprises, or contains, a material which swells upon contact with a liquid.

17. A concrete or grout element as claimed in claim 16, wherein the material comprises hydrotite.

18. A concrete or grout clement as claimed in any one of claims 11 to 17, wherein the reinforcement comprises a cage or mesh.

19. A concrete or grout element as claimed in any one of claims 11 to 18, wherein the reinforcement means comprises longitudinal bars.

20. A method substantially as herein described with reference to the accompanying drawings.

21. A concrete or grout element substantially as herein described with rctcrence to the accompanying drawings.

À@ (O +r PASTOR PEOPLE 1/i W _t Application No: GB0402635.7 Examiner: Dr Lyndon Ellis Claims searched: 1-21 Date of search: 8 June 2004 Patents Act 1977: Search Report under Section 17 Documents considered to be relevant: Category Relevant Identity of document and passage or figure of particular reference to claims X 1 and 11 GB 2172842 A at least (Onoda) Whole document X 1 and 11 US 4571124 A at least (Sumitomo) Whole document X 1 and 11 JP 58204216 A at least (Wade) Whole document X 1 and 11 JP 58213916 A at least (Tanaka) Whole document X 1 and 11 JP 59228523 A at least (Kobayashi) Whole document X 1 and 11 JP 60047119 A at least (Ishii) Whole document X 1 and 11 WO 81/02757 A at least (Asakura) Whole document Categories: X Document indicating lack of novelty or inventive A Document indicating technological background and/or state step of the art.

Y Document indicating lack of inventive step if P Document published on or after the declared priority date combined with one or more other documents of but before the filing date of this invention.

same category.

& Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.

Field of Search:

Search of GB, EP, WO & US patent documents classified in the following areas of the UKCW: E1H Worldwide search of patent documents classified in the following areas of the IPC07 An Executive Agency of the Department of Trade and Industry (at) C, (lKC 4 (=

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/f'l. ,}.< g rE02D l The following online and other databases have been used in the preparation of this search report i EPODOC, WPI, JAPIO l An Executive Agency of the Department of Trade and Industry