GB2420368A

GB2420368A - Method for breaking down concrete piles

Info

Publication number: GB2420368A
Application number: GB0523404A
Authority: GB
Inventors: John Shanks; Patrick Egan
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-11-18
Filing date: 2005-11-17
Publication date: 2006-05-24
Also published as: GB0425406D0; GB0523404D0; WO2006054094A1

Abstract

A method of breaking a concrete pile by isolating an outer portion of the pile from the top of the pile to an intended fracture level 30. Two embodiments are disclosed, firstly forming a slot 50 in the end of the pile 10 with the bottom 60 of the slot at the intended fracture level 30. The pile 10 can then be broken using conventional breaking methods, with the outer ring section 80 and the inner core section 70 removed separately. The second embodiment discloses a pile (110, fig.7) where at the time of casting an insert sleeve (152, fig.7), such as a hollow cylinder, is fitted with the lower end (156, fig.7) of the sleeve (152) at the same level as the cut off level (130, fig.7), resulting in an outer pile section (180, fig.7) similar to that produced by the first method. Both embodiments reduce the cross sectional area of the concrete pile to be broken in one fracture operation since the outer and inner portions, if there is an inner portion, can be broken separately. Therefore larger diameter piles can be broken cleanly by conventional pile crushers.

Description

Method for breaking down concrete piles The present invention relates to a

method of breaking concrete piles.

Reinforced concrete piles are widely used in civil engineering to provide a firm foundation for structures, particularly those built on soft or incompetent ground. Concrete piles can be pre-cast, or cast in situ.

Concrete piles are typically provided with reinforcement to improve the structural strength of the concrete, thereby allowing greater loads to be imposed on the pile. The reinforcement typically comprises steel bars, which extend along the length of the pile, i.e. in a direction substantially parallel to the longitudinal axis. The reinforcement may be fashioned into a mesh or cage.

The stages in the construction of a concrete pile when cast in situ, are outlined below. In the first stage, an auger is fitted with appropriate head, and is drilled into the ground to a predetermined and required depth. In the next stage, the auger is removed whilst high slump concrete is poured down the hollow core of the auger. An e.g. steel reinforcement cage is then pushed into the wet concrete, which causes the wet concrete to overspill at grourd level. In the final stage, and when the concrete is set, the ground level is reduced and the top section of the pile is broken down to a desired level, the so-called "cut off level". The removal of a top portion has two purposes. Firstly, the removal partially exposes the reinforcement and conveniently allows the next element of the building structure to be commected to the pile. For example, a pile cap or capping beam can be constructed on top of the broken down concrete pile. Secondly, breaking down of the top portion of the pile ensures that any concrete which may have become contaminated with soil and the like during the casting stage is removed, thereby ensuring that the quality of the concrete in the pile remains high.

The breaking down of the top section of a pile can be carried out either manually, or using mechanical means. The aim is to remove the top section of the pile without damaging the surface or structure of the pile beneath the cut off level. In a known method for casting and breaking down concrete piles, prior to the insertion of the reinforcement bars around which the concrete is cast, the portion of the bars extending higher than the cut off level is isolated from the concrete, for example by using foam sleeves, sheaths, or capping. This ensures that the concrete does not bond to the reinforcing bars when it sets, such that when a fracture is created at the cut off level, the portion of the pile to be broken off above the cut off level can be readily removed. Following casting of the pile, the next stage is to excavate away the ground to a depth of e.g. 100 mn below the cut off level. A circumferential cut is then made at the cut off level of the pile, for example using a circular saw. This cut, which is typically 10 mm deep, creates a failure plane at the cut off level, and ensures that the edge of the top section of the broken down pile is clean-cut. With piles having a diameter of approximately 750 mm or less, it is possible to cleanly break off the top section of the pile using a hydraulic pile crusher, which is typically dropped over the pile top down to the cut off level. The hydraulic pile crusher provides forces acting radially inwards of the circumferential edge, and upon actuation extends the failure plane previously created by the circumferential saw cut. The desired result is a fracture plane at the cut off level, whereby the fracture plane extends transversely through the pile i.e. perpendicular to the longitudinal axis of the pile. For larger diameter piles, for example having a diameter of greater than 750 mm, it is difficult to break off the top portion of the pile cleanly using known pile crushers, because the pile crusher has to induce a clean fracture across the entire diameter of the pile. With such larger diameter piles, known pile crushers are limited in the distance that they can induce a fracture through the pile, and often the transverse fracture created is only partial, and does not extend through the whole of the pile. The resulting fracture is rarely neat and clean, and the net result is that the breaking down of the pile has to be completed manually.

Although there are many health (and safety) hazards during pile cutting operations, it is widely acknowledged that the breaking down of the pile top to the cut off level is the most hazardous operation in terms of occupational health. This is because of the requirement to use vibratory tools such as breakers which are often manually operated by persons on site, and can cause hand-arm vibration syndrome (HAyS, formerly known as "vibration white finger"), whole body vibration syndrome (WBVS), as well as being associated with noise, dust and other manual handling hazards. Indeed, the potential hazards posed by the use of such tools has resulted in a health and safety ruling which has severely restricted the number of hours a person can work with such vibratory tools in a day. Complying with these health and safety restrictions poses further problems for construction companies - for example the manual breaking down of pile tops often requires more manpower than was required prior to the restrictions on use of vibratory tools. Thus, the health restrictions on hours of use of manually operated vibration tools, together with the associated problems of noise, pollution, and dust means that there is a need to develop a method which facilitates the clean and efficient breaking down of a concrete pile and which requires a minimum of mechanical breaking using manually operated vibrational tools.

A number of such methods have been developed in order to facilitate the breaking down of reinforced concrete piles and minimise the requirement for manual breaking.

One pile breaking method is disclosed in GB Patent No 2307504, and involves the removal of the unwanted pile section in one piece, the method exploiting the physics of crack propagation. As with the conventional method of breaking down a pile, the steel reinforcement above the cut-off level is prevented from bonding with the concrete by fixing isolating sleeves to the bars before the reinforcemert is lowered into position in the setting concrete. When the ground is excavated down to the cut off level, a hole (approximately 50 rmn diameter) is drilled horizontally into the concrete at the cut-off level to the centre of the pile. A standard hydraulic splitter or burster is inserted into the hole, actuated, and after around 30 seconds the concrete fractures transversely across the cut off level. An excavator can then be used to lift off the surplus concrete in a single piece via a lifting eye cast into the top surface of the portion to be removed. The problem with this method is that the fracture plane created at cut off level is rarely clean, and there is usually a requirement for manual trimming of the newly created top surface of the broken down concrete pile. Furthermore, the use of a hydraulic burster means that access space is required around the cut off level. If a number of concrete piles are set close together, or the cut off level is below ground level, it is not always possible to excavate the ground around the cut off level to provide sufficient access for the hydraulically actuated burster.

Other known methods also exploit the principle of crack propagation, for example as disclosed in WO 2004070121 WO8102757, JP62021924, and JP6l22l4l2. These methods generally rely on the expansion of fluids contained within a network of pipes and tubes cast into the concrete at the cut off level to form and propagate a crack. The methods initially involve isolating the reinforcing steel bars (for example as described above) followed by casting an assembly of pipes and tubes into the wet concrete at the cut off level. A fluid is then poured into the assembly of tubes, which expand as a result, thereby creating and propagating a transverse crack through the pile at the cut off level. The final stage of the method involves the removal of the top portion of the pile. The problem with these methods is that there is a requirement for precise setting at the cut off level of the assembly of tubes (into which the fluid is poured). Furthermore, the assembly of tubes has to be monitored as the concrete pile is hardening to prevent it from shifting position from the precise alignment required at the cut off level. This means such methods are time consuming and labour intensive.

The present inventors have devised a system which seeks to overcome the prior art disadvantages.

According to a first aspect of the present invention, there is provided a method of breaking a concrete pile comprising reinforcement means, said pile having a longitudinal axis and defining an outer edge in a plane perpendicular to said longitudinal axis, said reinforcement means in a portion of said pile which is to be broken down being isolated from said concrete forming said pile, said method comprising the steps of: (i) isolating an outer portion of said pile extending from the top of the pile downward to an intended level of the bottom of said portion to be broken down, (ii) applying to at least part of said outer edge at said intended level of the bottom of said portion to be broken down, forces which act inwards of said outer edge, said forces creating a fracture plane in said outer portion of said pile, said fracture plane being substantially perpendicular to said longitudinal axis at said intended level of the bottom of said portion to be broken down.

The intended level of the bottom of the portion to be broken down is known as the cut off level. The portion of the pile to be broken down above the cut off level is referred to as the top portion. The cut off level represents a predetermined level above which lies the portion of the pile to be broken down and removed, and below which is the remainder of the pile which will be used for support of the pile cap when the top portion is broken down and removed.

The pile may be cast in situ using known piling methodologies. Following setting of the concrete, the ground may be excavated away around the portion of the pile to be broken down (the top portion), thereby exposing the cut off level.

The pile may comprise reinforcement means which may for example be steel bars, which may be vertically extending, i.e. extending substantially parallel to the longitudinal axis of the pile. The reinforcement means may be held together in a spaced arrangement with a loop, band or skirt arrangement. The reinforcement means may be positioned within the pile following pouring of the concrete. The reinforcement means may be positioned toward the outer edge of the pile. The amount of reinforcement means required may vary, depending on the calculated structural loading of the pile.

To prevent the portion of the reinforcement means extending above the cut off level bonding with the concrete as it sets, the reinforcement means may be covered with a means to physically isolate it from the setting concrete. This isolation technique is well known in the art, and may for example comprise the use of foam sleeves, which may be positioned over the reinforcement means prior to its positioning in the setting concrete. The isolation of the reinforcement above the cut off level from the concrete may facilitate removal of the top portion after a fracture plane has been created at the cut off level. This means that following the fracturing of the concrete at the cut off level, the concrete portion above the cut off level can be removed easily, preferably in one or more large pieces.

The pile preferably comprises a longitudinal axis, the pile defming an outer edge in a plane perpendicular to the longitudinal axis.

The pile may be cylindrical. The pile may be e.g. a circular cylinder, or a square cylinder.

The pile may have a transverse cross section which is preferably circular, substantially circular, oval, elliptical, square, rectangular, or triangular.

The pile may be a right circular cylinder. The pile may have a diameter between 300-3000 mm.

Various sizes, shapes and dimensions of concrete piles are envisaged and will be well known to a person skilled in the art.

The step of isolating the outer portion may comprise forming a first slot in said pile about said longitudinal axis, said first slot extending from the top of the pile downward to said intended level of the bottom of said portion to be broken down and defining inner and outer portions of the pile and the step of applying forces generates a fracture plane which extends at least from said outer edge to a bottom edge of the slot. The first slot may be a continuous slot formed about the longitudinal axis. The first slot may be formed with known cutting tools, for example a coring machine, which may be diamond tipped. The first slot preferably extends to a lower depth which corresponds to the cut off level.

Depending on the size of the pile, the first slot may be formed at various distances between the longitudinal axis and the outer edge of the pile. The first slot may be a discontinuous or continuous slot.

The pile may be a circular cylinder or substantially right circular cylinder, the first slot being a continuous radial slot formed about the longitudinal axis. The first slot may be formed on an inner circumference about the longitudinal axis. The radius of the first slot may vary, depending on the diameter of the pile.

The first slot may be a core. The first slot is preferably formed with a coring machine, which is preferably mounted on a movement means, for example on the arm of an excavator, or the back of a truck. The coring machine may be comprised within a core drill rig. It is envisaged that a wide variety of coring machines which are known in the art could be utilised to form a first slot to a desired lower depth.

The first slot may define inner and outer portions of the top portion of the pile. The inner portion is the portion which extends from the slot toward the longitudinal axis. The outer portion is the portion which extends between the slot and the outer edge of the pile.

The lower depth of the first slot preferably only extends to the cut off level.

The inwardly acting forces may be applied to at least part of the outer edge of the pile at the cut off level. The inwardly acting forces may be applied around all of the outer edge of the pile at the cut off level. Preferably, the forces are applied evenly around the outer edge of the pile. The forces preferably act inwardly, i.e. from the outer edge toward the longitudinal axis of the pile. Where the pile is a circular pile, the forces preferably act radially inwards of the outer edge.

The forces may be applied using a pile crusher, which may be hydraulically actuated.

Various types of tools capable of providing the inwardly acting forces are envisaged and will be well known to a person skilled in the art. For example, a known pile crusher comprises a plurality of hydraulically actuated rams spaced in a circular arrangement, each ram having a chisel point pointing radially inwards. The pile crusher is preferably dropped over the pile, and positioned so that the chisel points lie around the outer edge of the pile at the cut off level. Upon actuation of the hydraulic rams, the chisel points contact the outer edge of the pile at the cut off level, and induce a transverse fracture extending from the outer edge to the lower depth of the slot. Pile crushers may be used where piles are individually set at some distance from each other. Where the piles are set close together (for example in a contiguous pile wall), it may not be possible to use a pile crusher due to space restrictions. In this situation, the inwardly acting forces may be applied using other means - for example using a haninier, or other tool, which may be attached to an excavator arm, and which may be applied to at least part of the outer edge of the pile at the cut off level. For example, a hammer may be used to apply inwardly acting forces to one side of the pile, thereby creating a fracture plane. Alternatively, an excavator arm fitted with an appropriate tool may be used to knock the pile on one side, thereby creating a fracture.

The inwardly acting forces may create a fracture plane in at least the outer portion of the pile, the fracture plane being induced at the cut off level, being substantially perpendicular to the longitudinal axis, and extending between the outer edge and the lower depth of the first slot.

The function of the first slot is to decrease the distance over which a fracture extending from the outer edge of the pile has to propagate. Thus, the use of a slot means that piles which could not be broken down cleanly by virtue of their large size, can now be broken down using known and conventional pile crushers.

Prior to step (ii) the method may comprise the step of: (a) forming a second slot in the outer edge of the pile at the intended level of the bottom of the portion to be broken down, the second slot extending inwardly of the outer edge in a plane substantially perpendicul& to the longitudinal axis.

Prior to step (ii) the method may comprise the step of removing the inner portion of the pile, and optionally additionally comprising the step of: (iii) removing the outer portion of the pile.

The method may further comprise the step of: (iii) removing at least one of the outer portion and the inner portion of the pile.

The method may comprise the step of removing the outer portion and the inner portion of the pile.

Thus, prior to applying the forces which act inwards of the outer edge the method may comprise the step of removing the inner portion of the pile and optionally the outer portion of the pile. The inner portion may be broken off at the cut off level, for example by using mechanical means, e.g. a hammer. The inner portion can thus be removed for e.g. disposal or recycling, prior to the creation of the fracture in the outer portion of the pile.

Alternatively, a first slot can be formed about the longitudinal axis, and the forces acting inwardly of the outer edge may be applied, thereby inducing a fracture plane (as described above). At this stage, the outer portion can be cleanly removed, because of the fracture extending between the outer edge and the slot. The inner portion may then be removed, for example as described above. Thus, after a first slot is formed, it is possible to remove the inner portion.

Following the application of the forces acting inwardly at the cut off level, the method may comprise the step of removing at least one of the inner and outer portions of the pile.

Preferably, both of the outer and inner portions are removed. This removal step can be performed in any desired order, i.e. removal of the inner portion followed by the outer portion, or vice versa. Removal of both portions simultaneously may be effected, for example using a mechanical lifting means such as a crane.

The removal of the inner and outer portions exposes an end face, which is preferably undamaged by the process of breaking down the top portion of the pile. The end face is preferably horizontal, and preferably lies at the cut off level, in a plane substantially perpendicular to the longitudinal axis of the pile. It is desirable that the end face created by breaking down the pile is flat, with a neat surface and tidy edges. The end face is preferably suitable for use in further stages of a building operation, and preferably requires no manual trimming. Preferably, the first slot does not extend below the cut off level, because the end face which is exposed following removal of the inner and outer portions may not he horizontal, and may not be suitable for further building operations. However, some degree of tolerance in the extension of the first slot is envisaged, such that the end face may be tidied up for further building operations if necessary.

The second slot may extend inwardly from the outer edge to a depth of around 5-30 mm.

The second slot may extend inwardly from the outer edge to a depth of around 10-20 mm.

The second slot is preferably formed in the outer edge of the pile, and more preferably at the cut off level.

The second slot may be a continuous slot formed in the outer edge. Where the pile is a circular cylinder or a substantially right circular cylinder, the second slot may be a continuous circumferential slot formed in the outer edge of the pile.

The second slot may be discontinuous and may be formed in part of the outer edge at the cut off level.

The second slot may be formed by a cutting tool, for example with a saw, e.g. a circular saw. The second slot preferably facilitates the creation and propagation of a transverse fracture at the cut off level, thereby ensuring that the outer edge of the newly created end face is neat and tidy, and suitable for further use in building operations.

The second slot may serve as a guide for the e.g. chisel points of a pile crusher.

The inner and outer portions may comprise connecting means. The connecting means may be a lifting point, such as a metal loop or eye, which may be cast into the outer and or inner portion of the pile. The connecting means may connect to a lifting means such as crane or excavator arm, thereby facilitating removal of each portion following the creation of the fracture plane at the cut off level.

- 12 - The method may comprise the step of applying a pile crusher to the outer portion of the pile.

One of the advantages of the present invention is that the top portion of a pile can be S broken down easily, allowing easy removal of the outer and inner portions as whole pieces of concrete. Because the fracture only has to propagate inwardly to the lower depth of the first slot, a clean fracture can be created for piles of very large diameter. This is in contrast to known methods of breaking down piles, where the fracture created for piles having a large diameter is typically only partial, meaning that the top portion of the pile can not be removed cleanly and neatly. A partial fracture means that there is a requirement for manual trimming to finish the job.

Alternatively, the step of isolating said outer portion may comprise a step of locating an insert sleeve in a central portion of the pile at the time of casting, which insert sleeve is extends downwards from above the top of the pile to the intended level of the bottom of said portion to be broken down. In this case, the step of applying forces may generate a fracture plane which extends at least from said outer edge to a bottom edge of the insert sleeve. This method may comprise the step of fitting the insert sleeve to the reinforcement means. Then the concrete may be poured around the insert sleeve and reinforcement means so as to form the pile. Alternatively, the reinforcement means, with the insert sleeve fitted to it may be inserted into the concrete for forming the pile when the concrete is wet.

The location of the insert sleeve may be co-axially with the pile.

According to this alternative method forces are applied to the outer edge of the pile at the intended level of the bottom of the portion to be broken down, as is described above, in the same way as for the other method described.

- 13 - The present invention further provides an insert sleeve suitable for use in the alternative method described above, which insert sleeve comprises a hollow sleeve having closed upper and lower end faces. The outer corner of the lower end surface may be formed as a sharp edge so as to promote the formation of the fracture plane extending from the outer edge to the bottom edge of the insert sleeve. The lower end surface of the insert sleeve may be co-planar with the fracture plane. The insert sleeve may be cylindrical and may be made of metal, in particular steel, or high density plastic. The insert sleeve may additionally comprise at least one radially outwardly extending elements for fixing the sleeve to the reinforcement means.

The fact that the method of the present invention allows for easy removal of the top portion of a pile in one or more portions means that there is no requirement for manual trimming to finish thejob. This not only minimises the risks and dangers associated with vibrational tools, but also means that the amount of dust and noise created is minimised, both of which can be a safety hazard. Thus, from a health and safety perspective, the method of the present invention is significantly advantageous over known methods.

The invention will now be described with reference to Figures 1-6 of the drawings where: Figure 1 shows a longitudinal cross section (Figure 1 a) and a top view (Figure 1 b) of a concrete pile following casting in Situ, with the ground excavated around the cut off level; Figure 2 shows a concrete pile, in longitudinal cross section around the cut off level (Figure 2a), and as a top view (Figure 2b); Figure 3 shows a longitudinal cross section of a concrete pile comprising an inwardly extending horizontal second slot at the cut off level (Figure 3a), and a top elevation of same (Figure 3 b) ; Figure 4 shows a concrete pile following removal of the outer portion longitudinal cross section(Figure 4a), and as a top elevation (Figure 4b); Figure 5 shows a side elevation of a concrete pile following removal of the outer portion; Figure 6 shows a side elevation of a concrete pile following removal of the outer and inner portions; Figure 7 shows a longitudinal cross section of a concrete pile before removal of the outer portion and incorporating an insert sleeve 10;and Figure 8 shows a transverse cross section of the concrete pile of Figure 7.

Referring to Figures 1-6, a circular cylindrical concrete pile (10) is cast in situ in the ground using conventional piling techniques. The concrete pile (10) comprises reinforcement bars (15) arranged around an inner circumference of the pile (10). The bars (15) extend substantially parallel to a longitudinal axis (20) of the pile (10). The ground (18) is excavated around the pile (10), exposing the cut off level (30). The portion of the bars (15) extending above the cut off level (30) are isolated from the concrete through the use of foam sleeves (not shown).

Referring to Figures 2-6, the longitudinal axis (20) defines an outer edge (40) in a plane perpendicular to the longitudinal axis (20). The pile (10) has a top surface (45). A downwardly extending first slot (50) is cut into the top surface (45) about the longitudinal axis (20), the first slot (50) extending to a lower depth (60) which is at the same level in the pile (10) as the cut off level (30). The first slot (50) defines an inner portion (70) and an outer portion (80). The first slot (50) is a continuous radial slot formed about the longitudinal axis (20). - 15-

Referring to Figure 3, a horizontally extending second slot (90) is cut into the outer edge (45) of the pile (10) at the cut off level (30). The second slot (90) is a continuous circumferential inwardly extending slot defining an inner margin (95). The second slot serves as a failure plane, through which a fracture extending from the inner margin s propagates to the lower depth of the first slot (50).

Referring to Figures 2 and 3, inwardly acting forces are applied along the plane depicted by arrows (A), causing a transverse fracture to be created through the plane of the cut off level (30). In Figure 2, the fracture extends from outer edge 45 to the first slot 50. In Figure 3, the fracture extends from the inner margin (95) of the horizontally extending second slot (90) to the first slot (50). Inwardly acting forces are applied through the use of known pile crushers or other mechanical breaking means such as hammers. Following the creation of the transverse fracture in the outer portion (80), the outer portion (80) is removed in one piece, for disposal or recycling.

Referring to Figures 4-6, following removal of the outer portion (80), steel bars (15) are exposed. The inner portion (70) remains attached tothe pile (10). Mechanical force applied at the point depicted by arrows (B) facilitates the easy removal of inner portion (70) for disposal or recycling. Removal of the inner portion (70) completely exposes end face (100), which can be utilised in further building operations.

Referring now to Figures 7 and 8 a circular cylindrical concrete pile (110) is cast in situ in the ground using conventional piling techniques. The concrete pile (110) comprises reinforcement bars (115) arranged around an inner circumference of the pile (110). The bars (115) extend substantially parallel to a longitudinal axis (120) of the pile (110). The ground is excavated around the pile (110), exposing the cut off level (130). The portion of the bars (115) extending above the cut off level (130) are isolated from the concrete through the use of foam sleeves (132) .

The pile (110) has a top surface (145) and a side surface (140). At the time of casting of the pile an insert sleeve (152) is fitted to the bars (115). The insert sleeve (152) and the bars (115) may be located in the hole into which concrete is poured to case the pile. More conventionally, the inserts sleeve (152) and the bars (115) are pushed into the wet concrete during the pile casting process. The insert sleeve (152) may comprise a hollow cylinder closed at its upper end by an upper end plate (154) and closed at its lower end by a lower end plate (156). A central axis of the insert sleeve (152) is co-axial with the axis (120).

The insert sleeve (152) is held in place by a pair of radially extending and axially spaced rods (158). Each rod (158, 160) extends through the insert sleeve (152) and the ends of each of the rods (158, 160) are fixed to radially opposing pairs of the bars (115). The rods (158, 160) are fixed to the bars (115) by tying wire (164). The insert sleeve (152) is positioned so that the external face of the lower end plate (156) is at the cut off level (130).

The insert sleeve (152) extends upwardly for a distance sufficient that the upper end plate (154) of the insert sleeve lies above the level to which the pile is cast, so that it extends above the upper surface (145) of the cast pile (110). The rods (158, 160) are fitted to the insert sleeve by nuts (162) which are receved on threaded portions of the rods so that the nuts (162) abut the external surface of the insert sleeve. The rods (158, 160) may be threaded along their entire length. The insert sleeve (152) may be made of metal, for example steel or may be made of high density plastic. The outer corner of the interface between the cylindrical portion of the insert sleeve (152) and the lower end plate (156) is preferably a sharp corner, so as to help to induce cracks at the cut off level (130) when the pile (110) is broken down.

With the insert sleeve (152) fixed in the position described above in relation to Figures 7 and 8, the pile (110) is cast. The result is a pile (110) in which the insert sleeve (152) is partially embedded so as to define an outer portion (180) of the concrete pile (110) which surrounds the insert sleeve (152). A horizontally extending slot, shown by dotted lines (190) is cut into the outer edge (140) of the pile (110) at the cut off level (130). The slot (190) is a Continuous circumferential inwardly extending slot defining an inner margin (195). The slot serves as a failure plane, through which a fracture extending from the inner margin propagates to the sharp lower corner of the insert sleeve (152).

Inwardly acting forces are applied along the plane depicted by arrows (A), causing a transverse fracture to be created through the plane of the cut off level (130). In Figure 7 the fracture plane extends along the cut off level (130) from from the inner margin (195) of the horizontally extending second slot (90) to the sharp lower corner of the insert sleeve (152). Inwardly acting forces are applied through the use of known pile crushers or other mechanical breaking means such as hammers. Following the creation of the transverse fracture in the outer portion (180) of the pile (110), the outer portion (180) is removed, with the insert sleeve (152), in one piece, for disposal or recycling. Following removal of the outer portion (180), the steel bars (115) are exposed. - 18-

Claims

Claims 1. A method of breaking a concrete pile comprising reinforcement

means, said pile having a longitudinal axis and defining an outer edge in a plane perpendicular to said longitudinal axis, said reinforcement means in a portion of said pile which is to be broken down being isolated from said concrete forming said pile, said method comprising the steps of: (i) isolating an outer portion of said pile extending from the top of the pile downward to an intended level of the bottom of said portion to be broken down, (ii) applying to at least part of said outer edge at said intended level of the bottom of said portion to be broken down, forces which act inwards of said outer edge, said forces creating a fracture plane in said outer portion of said pile, said fracture plane being substantially perpendicular to said longitudinal axis at said intended level of the bottom of said portion to be broken down.
2. A method as claimed in claim 1 wherein the step of isolating the outer portion comprises forming a first slot in said pile about said longitudinal axis, said first slot extending from the top of the pile downward to said intended level of the bottom of said portion to be broken down and defining inner and outer portions of the pile and the step of applying forces generates a fracture plane which extends at least from said outer edge to a bottom edge of the slot.
3. A method as claimed in claim 2, said method prior to step (ii) comprising the step of: (a) forming a second slot in said outer edge of said pile at said intended level of the bottom of said portion to be broken down, said second slot extending inwardly of said outer edge in a plane substantially perpendicular to said longitudinal axis. - 19-
4. A method as claimed in claim 2 or claim 3, said method prior to step (ii) comprising the step of removing said inner portion of said pile, and optionally additionally comprising the step of: (iii) removing said outer portion of said pile.
5. A method as claimed in claim 2 or claim 3, said method further comprising the step of: (iii) removing at least one of said outer portion and said inner portion of said pile.
6. A method as claimed in claim 5, step (iii) comprising removing said outer portion and said inner portion of said pile.
7. A method as claimed in any of claims 2 to 6, said first slot being a continuous slot formed about said longitudinal axis.
8. A method as claimed in claim 7, said first slot being a core.
9. A method as claimed in any of claims 3-7, said second slot being formed continuous in said outer edge.
10. A method as claimed in any of claims 3-9, said second slot extending inwardly from said outer edge to a depth of 5-30 mm.
11. A method as claimed in any of claims 2 to 10, said first slot being formed with a coring machine.
12. A method as claimed in any of claims 3-11, said pile being a substantially right circular cylinder, said first slot being a continuous radial slot formed about said longitudinal axis.
13. A method as claimed in claim 12, said second slot being a continuous circumferential slot formed in said outer edge.
14. A method as claimed in any of claims 2 to 13, said inner and outer portions comprising Connecting means.
15. A method as claimed in any of the previous claims, step (ii) comprising applying a pile crusher to said outer portion of said pile.
16. A method as claimed in claim 1 wherein said step of isolating said outer portion comprises a step of locating an insert sleeve in a central portion of the pile at the time of casting, which insert sleeve extends downwards from above the top of the pile to the intended level level of the bottom of said portion to be broken down.
17. A method as claimed in claim 16 wherein said step of applying forces generates a fracture plane which extends at least from said outer edge to a bottom edge of the insert sleeve.
18. A method according to claim 16 or claim 17 comprising fitting the insert sleeve to the reinforcement means.
19. A method according to any one of claims 16 to 18 comprising the step of locating the insert sleeve co-axially with the pile. -21 -
20. An insert sleeve suitable for use in the method according to any one of claims 16 to 19 comprising a hollow sleeve having closed upper and lower end faces.
21. An insert sleeve according to claim 20 wherein the outer corner of the lower end surface is sharp.
22. An insert sleeve according to claim 20 or claim 21 wherein the insert sleeve is cylindrical.
23. An insert sleeve according to any one of claims 20 to 22 wherein the insert sleeve is made of metal, in particular steel, or high density plastic.
24. An insert sleeve according to any one of claims 20 to 23 additionally comprising radially outwardly extending elements for fixing the sleeve to the reinforcement means.