Hydraulic Pile Cap Removal
A pile cage (2) has a reinforcement structure (4) having a first part (8) adapted to remain in a pile, the first part terminating at a predefined cut-off level (20), and a second part (10) that is protected in order to debond it from concrete cast around it. A split-wailed annular tube (30) is located at the cut-off level (20) and is connected to a supply of pressurised fluid after the concrete has been poured and set. The tube (30) expands under pressure initiating a crack that is propagated by the escape of fluid from the slit (32) towards a centre of the pile at the cut-off level (20). The entire cracked central surface of the cast pile acts as a hydraulic jack separating the pile cap (104) from the remainder of the pile (102).
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The present invention relates to the breaking of concrete piles in order to remove the surplus concrete cap or head.
Reinforced concrete piles are widely used in civil engineering for retaining walls and foundations for structures. In accordance with the Institution of Civil Engineers “Specification for Piling and Embedding Retaining Walls” published on 17 Apr. 1996 under ISBN 0-7277-2566-1, it is taught to cast a pile to a level above a specified cut-off so that there remains a pile head or cap that must be removed. This is to ensure that:
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- (a) there is a sound concrete connection with the pile when it is incorporated into the remainder of the structure; and
- (b) the concrete comprising the top portion of the pile is of good quality and is not, as would otherwise be the case, contaminated with soil or poorly compacted.
It is standard practice to cast the concrete of the pile so that it covers the entirety of the pile cage or pile reinforcement.
Traditionally, the breaking of concrete piles is carried out by manual labour and is a slow, arduous and expensive process, which produces a considerable amount of loose debris for disposal. Even if mechanical means are used, close supervision is necessary as the cut-off level is approached, in order to prevent damage to the pile below the cut-off level.
The use of hand-held pneumatic tools, as employed in manual breaking processes, is associated with industrial injuries including hand-arm vibration syndrome (“HAVS”) commonly known as vibration white finger.
Other health and safety issues arising from manual methods include noise and the risk of injury from displaced concrete fragments.
One method of breaking a reinforced concrete pile, which is in current use, is described in WO9736058 Merritt & Elliott). In this method the reinforcement in the pile head to be removed is treated so that it is debonded from the concrete of the pile, a hole is formed in the pile at the desired cut-off level, and a hydraulic tool is applied in the hole to split the pile in a substantially transverse plane. Use of this method reduces the risk of industrial injury but does not eliminate it. The concept of debonding is also described in JP58-11218 (Yahagi Kensetsu KKK) and WO8102757 (Asakura).
Chemical methods of splitting the pile head at cut-off level are also used. Such methods include the RECEPIEUX® technique, which uses expanding grout in conjunction with debonding of the reinforcement to break the piles down. It is also possible to leach out the cementious material, above the cut-off level from the wet concrete of a cast-in-situ pile as part of the construction process. While these chemical techniques avoid the necessity for the use of vibrating hand tools, there are safety and environmental implications in keeping and using chemicals (which may be volatile) on site. There is also an explosion risk if the process is not operated correctly.
Asakura also attempts to eliminate the need to use mechanical tools by the use of a hydraulic method. A substantially flat metal pipe is placed into the pile cage at the cut-off level. After casting is complete and the concrete has hardened, fluid is supplied with increasing pressure to this pipe to break off the pile cap. The pile cap may then be lifted and removed. As illustrated in FIG. 2 of Asakura, the metal pipe is annular in plan view and is shown as tied to the pile cage. The coupling for supply of pressurised fluid is shown positioned within the side wall of the pile and excavation would be necessary in order to locate these connectors once the pile had been cast. Crack propagation, especially around the perimeter of the pile, using the Asakura method is unpredictable.
Since the priority date of this application GB 23898333 (Skanska) has been published. Skanska teaches a hydraulic method similar to Asakura in which an expandable, ring-shaped element or annular tube is located preferably inside the reinforcement. In one embodiment the element is a tube is made of PVC, rubber, polyurethane, neoprene, butyl or other flexible material and is pressurised with water or hydraulic fluid. In another the element is formed of or loaded with HYDROTITE®—a material that swells when it comes into contact with water. These embodiments work in the same way as Asakura and, although effective for splitting the cap, crack propagation is unpredictable.
Skanska also states that: “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.” This loop is not further illustrated or claimed.
Skanska suggests the use of a frame to mount its expandable element.
TECHNICAL PROBLEMThe present invention therefore addresses the technical problem of controlling crack propagation in pile cap removal using hydraulic power.
As a subsidiary technical problem it is desired to achieve hydraulic pile cap removal without the use of excessive pressures that might result in accidents or damage to the piles.
SOLUTION OF THE INVENTIONThe present invention provides a pile cage comprising a reinforcement structure having a first part adapted to remain in a pile, the first part terminating at a predefined cut-off level, and a second part that is protected in order to debond it from concrete cast around it; a crack-inducing ring aligned at the cut-off level; and means for supplying pressurised fluid to the crack-inducing ring; characterised in that the cage further comprises a crack-directing feature on or adjacent the crack-inducing ring and a crack-attracting feature located at the cut-off level outside the crack-inducing ring.
The preamble of the above claim is based on Skanska or Asakura, but differs from both pieces of prior art in that the crack propagation is controlled and restricted to the cut-off level. This is more effective in achieving a crack in the correct plane than the prior art approach of aiming to ensure that the forces created by the expandable element resolve only parallel to the axis of the pile—usually vertical. The application of pressure to a tubular expandable element will produce a radial outward force in all directions. It is difficult to ensure that the pressure at all points around the ring is the same with a single connection point. In Asakura one end of the metal pipe is closed and the other end is connected to a hose capable of supplying a pressurizing fluid. Without a crack-attracting feature the crack may travel from the ring at any angle up to 45° above or below the cut-off level. If the crack were to travel substantially downwards from the cut-off level in any part of the pile it would result in the crack being formed below the debonded section of the pile head thus precluding the easy removal of the pile head. Inappropriate management of this event in the field could result in a structurally weakened pile. If the crack were to travel substantially upwards from the cut-off level in any part of the pile it would leave a projection that would require further remedial work with percussion tools, thereby negating the main advantage of the invention.
Preferably the crack-inducing ring has a slit or frangible region in a portion of its wall facing towards a centre of the pile. Such a slit is adapted to permit fluid to flow substantially inwardly towards a centre of the pile. In this embodiment the crack is propagated and the fluid escapes rather than relying solely on the force created by an expanding metal pipe as described in Asakura. If the Asakura pipe were to burst then its connection with the pile cage would result in the debonding material creating a preferential path for the escape of the fluid.
The pressurised fluid entering the crack-inducing ring initiates a crack whether by means of the expansion of the ring or directed high pressure water flow or a combination of both effects. The crack-attracting feature situated outside the crack-inducing ring ensures that the crack remains substantially planar as it reaches the edge of the pile. By allowing the fluid to flow out towards the centre of the pile, the crack that is initiated is also driven in a substantially planar direction towards the centre of the pile. The resultant surface of the concrete is within design tolerances and only minimal trimming is necessary. This greatly reduces the health and safety risks associated with the use of hand operated tools and provides a safer working environment.
In order to enable pile cages to be fabricated easily, the present invention teaches the use of an assembly comprising a planar support frame having an inner annular member supporting the crack-inducing ring, a concentric outer annular member that is or supports the crack-attracting feature, and a plurality of spaced spokes holding the members together.
Therefore, all the essential parts of the invention that enable the pile cap to be removed hydraulically can be assembled together off-site as a single rigid unit. This saves time on-site as the assembly simply has to be lowered over the reinforcement bars and secured in place at the cut-off level. Furthermore, as the outer member of the assembly that fits outside of the reinforcement bars and preferably serves as the crack-attracting feature is in the same horizontal plane as the crack-inducing ring, there is no need for manual alignment. By a suitable asymmetric spacing of the spokes, the assembly can be made to fit over various numbers and configurations of reinforcing bars typical of the pile size for which it is made.
The present invention also provides a method of breaking a reinforced concrete pile comprising the steps of placing a fluid-receiving means into a pile cage at a cut-off level, protecting an upper part of the pile cage with debonding material, casting the pile, and supplying pressurised fluid to the fluid-receiving means, characterised in that the fluid-receiving means is adapted to permit fluid to flow substantially inwardly towards a centre of the pile at the cut-off level.
Ideally the means for supplying pressurised fluid to the fluid-receiving means comprises a pump that enables the application of pressure to be controlled. Use of excess pressure in this type of device can result in the creation of a shock wave within the concrete that effectively explodes the pile apart and may have an undesirable impact on the remainder of the pile structure. A controllable pressure source allows the method to be used with a variety of pile sizes.
After the crack has been created by the application of the pressurised fluid, there is no concrete connection between the structural pile and pile head. When such a pile head is grasped by a hydraulic grab or crane, it can simply be lifted off and removed leaving the second part of the reinforcement intact. The fluid-receiving means can be reused several times. As a connection point for the fluid supply is preferably located at or near the top of the pile it is easy to access without the need for any excavation. With a connection point at the top of the pile, the crack can be formed prior to excavation. This enables the piles to be cracked as soon as they are set, when the concrete is relatively weak and easy to crack. It also reduces the risk of construction plant damaging the main pile body prior to or during excavation and significantly reduces the time spent on the whole piling operation.
Other features of the invention are defined in the appended claims.
ADVANTAGES OF THE INVENTIONThe method of the invention avoids the need for mechanical tools with their associated HAVS risks. It is fast and economical. In addition the method is safer than Asakura as the pressures required are lower because the fluid is able to act over the entire cracked area of the pile.
The method of the invention considerably improves the accuracy of the cut.
BRIEF DESCRIPTION OF THE DRAWINGSIn order that the invention may be well understood, some embodiments thereof will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which:
A pile cage 2 comprises a reinforcement for a pile. The reinforcement is typically fabricated from an assembly of rebars 4 held together in the desired configuration by means of a coil or links (not shown). Steel mesh may also be used to create the reinforcement. The pile cage 2 has a first part 8 that remains in situ in a cast pile and a second part 10, which will be in a pile head that will be incorporated into reinforced concrete slabs or caps. The first and second parts 8 and 10 are separated by the plane of a cut-off level indicated at 20.
The rebar 4 of the second part 10 of the reinforcement 2 is protected by means of debonding foam tubing 22. The type of foam tubing that is slit axially like pipe insulation is preferred as this can be easily assembled to the rebar 4 in order to form a protective layer. Other debonding products or techniques may be employed. The debonding terminates at the cut-off level 20.
A crack-inducing ring 30 is positioned at the cut-off level 20. A crack-inducing ring 30′ is shown in profile in
The slit 32 is positioned at the level of the cut-off plane 20 so that it faces the centre of the pile cage. The tube 30 can be supported by an inwardly projecting limb 26 of a profile support L bars 28 secured to the sleeved rebars 4 at the correct level. A series of, say, six spaced profile support bars 28 are needed for a large pile cage. The flattened part 24 of the crack-inducing ring 30 is seated against a face of the limb 26 to ensure the slit 32 is correctly positioned. For large pile cages 2 these components are assembled on-site and held together by, for example cable ties and tape.
The silt 32 is formed between two wedge-shaped fins 34 moulded as part of the tube 30. The fins create a beak-like structure 38 that serves as a crack-directing feature. In the ex-factory condition the slit 32 is closed by a thin frangible film 36 of rubber material, which is an artefact of the moulding process.
The crack-inducing ring can be assembled from a length of tubing of an appropriate length, which has been extruded to the required profile. The tubing has two free ends 40. A pressure supply line hose 50 may be coupled to a free end 40 by inserting it into the open end 40. The ends 40 may be taped closed.
To complete the assembly a pressure supply line hose 50 is inserted into one of the two free ends 40 of the length of tubing 30 and secured in place with a plastic cable tie.
In an alternative embodiment illustrated in
In either embodiment the hose 50 is protected with debonding foam tubing 22 and is attached to a rebar 4 and passes out of the top of the pile cage or is directed out of the cage at a suitable position. A remote end 60 of the hose 50 is fitted with a standard connector 64, to enable it to be connected by a pressure line 66 to a pump (not shown). A suitable pump for this application for use with very large piles is a MADAN® Mark 7 air-driven pump capable of producing an output pressure of 240 bar with an air supply of 7 bar. A pump that enables the application of pressure to be controlled is preferred so that a pressure appropriate to the size of the pile can be applied. Pressures far less than 240 bar will achieve an acceptable result and the appropriate pressure level can be ascertained by simply ascertained experimentally for any pile size.
The annular split tube 30 acts as a fluid-receiving means to receive pressurised fluid via the pressure line 64 and hose 50 from the pump. The tube 30, because it is embedded in concrete, will initially fill with the fluid. As the pressure builds up a crack will be initiated around the tube in the same way as in Asakura, but now the fluid will be forced out between the fins 34 breaking the thin film 36 of rubber material closing the slit thereby permitting the fluid to escape into the pile, providing a jacking mechanism separating the pile head from the remaining pile at the cut-off level.
The material of the tubing 30 must be sufficiently rigid to avoid being displaced during the concrete pour. This may be achieved by reinforcing that part of the tube wall opposite the slit 32 or inserting a rigid reinforcement link 66 into the tube 30.
A crack-attracting feature 70 is needed in the cut-off plane 20 outside of the rebars 4. A ring of plastics material such as 32 millimetre spiral ducting, hosing or debonding sleeving will serve as a crack-attracting feature 70 and can readily be assembled to the rebar at the appropriate level by means of cable ties as shown in
Support Frame for Smaller Piles
For piles of diameters 600 to 750 mm, it is less convenient to assemble the crack-inducing ring and crack-attracting feature 70 to each pile cage on site. This becomes a fiddly operation due to the reduced rigidity of the rebar cage and alignment errors may arise.
The reinforcement for such piles may only comprise vertical rebars 4 spaced around the periphery of the pile with nominal helical ties. Depending on the specification there may be four, five, six or more rebars.
In this case the solution is to provide an assembly 110 on a support frame 112 that can be dropped over the ends of the rebars 4 as a completed assembly of frame, crack-inducing ring 30? and crack-attracting feature 70. Two such designs are illustrated in FIGS. 6 to 9.
As shown in
The inner member 114 shown in
The wire frame must be assembled by welding the wires and this adds to the cost. Therefore an alternative solution is provided by the plastics member illustrated in
For both support frame embodiments it is preferable to have frames 110 that can be used with a variety of rebar designs possible with the pile diameter for which the frame 112 has been manufactured. This can be achieved by positioning the spokes 118 asymmetrically as shown in
As before the tube 30 is secured to the inner member 114 with plastics cable ties (not shown).
The assembly 110 is fitted to the pile cage 2 by lowering it over the rebars 4 and securing it in position at the cut-off level 20. The outer ring 116 fits outside reinforcement structure 4 and the inner ring 114 fits inside the reinforcement structure 4.
Alternative Tube Design
Instead of a single annular tube 30 serving as the fluid-receiving means, it is possible to locate discreet fluid-receiving means each connected by means of a pressure line 64 to a pump in the cut-off plane 20 as shown in
A U shaped annular flow control moulding, 96 for example a moulding similar in form and construction to a bicycle tyre is fitted in the cut-off plane 20 in order to receive any fluid escaping from the plates 90 and to restrict its flow. A moulding in the form of a tyre makes a suitable flow control shield to prevent fluid reaching the debonding foam. In this embodiment, the combination of the plates 90 and the flow controller 96 acts as the fluid-receiving means.
Method of Use
The method of use of such a pile cage 2 will now be described.
The reinforcement 2 is prefabricated and the second part 10 of the reinforcement has debonding tubing foam 22 carefully fitted to the rebar 4 above the cut off level 20.
The fluid-receiving means, either tube 30 or assembly of plates 90 and flow controller 96 is fitted inwardly of the reinforcement and secured to the debonded rebar 4. The slit 32 of the tube 30 is positioned facing towards the centre of the pile at the required cut-off level 20. A crack-attracting feature is also fitted outwardly of the reinforcement. Where a prefabricated assembly 110 is used this is fitted over the reinforcement and secured to the debonded rebar 4 at the required cut-off level 20.
The hose 50 is then connected to the fluid-receiving means as previously described. The hose 50 is protected by debonding foam 22 and passed out of the top or side of the pile cage 2. The hose 50 and the debonding foam 22 are kept in place by attaching them to a rebar 4.
The pile is bored to the desired depth and fully assembled cage 2 installed.
The pile is then concreted resulting in a pile as illustrated in
The pile is allowed to set for typically two to five days.
The connector 64 is connected to a pump (not shown). In the embodiments of FIGS. 1 to 10 the pump pumps pressurised water down the hose 50 into the fluid-receiving means 30. In the embodiment of
In the third embodiment of
Once a crack has been achieved the hydraulic lines 64 are disconnected and removed. The severed pile head 104 can then be lifted vertically by means of a mechanical grab. As the pile head is pulled upwardly the hose 50 will pull out of the connection piece 42, open end 40 of tube 30 or plates 90 as appropriate leaving these in situ on the surface of the cut-off plane. It is then straightforward to separate the fluid-receiving means and crack-attracting features 70 from the pile cage 2 and remove these items for re-use with another pile cage. If an assembly 110 on a support frame 112 has been used removal is even simpler. The debonding 22 is removed and the pile is finished off. In the embodiment of
All the components can then be re-used with another pile cage.
Variations
In place of the continuous slit in the annular tube 30, a series of apertures or perforations may be provided at the cut-off level 20. A projecting fin or other formation adapted to lie in the cut-off plane 20 may be provided between the apertures in order to ensure that the crack propagates in the correct plane.
Where crack-inducing plates 90 are used, these may comprise a compressible void-former of the required shape. When fluid is supplied to such compressible plates, a void is formed at the interface between the concrete and the void-former and this opens up a path for the fluid received by the plate 90 to flow into. As the pressure increases a crack will be initiated by the feature 92.
The fluid will then pass along this void and crack creating a jacking mechanism and induces the crack in the cut-off plane.
It will be appreciated that the pile cage and pile cap removal system described above allows the programme of pile cap removal to be shortened considerably relative to existing methods. The hydraulic pump, if air powered, can readily be moved from pile to pile with its compressed air supply. The time taken to split a pile using this method can be reduced to minutes. The removed pile heads can then be lifted away separately as the programme permits. Note that the positioning of the connectors 64 in an upper surface means that the piles do not need to be excavated before being split.
Claims
1. A pile cage (2) comprising a reinforcement structure (4) having a first part (8) adapted to remain in a pile, the first part terminating at a predefined cut-off level (20), and a second part (10) that is protected in order to debond it from concrete cast around it; a crack-inducing ring (30, 96) aligned at the cut-off level (20); and means (42, 44, 50, 58, 62, 64, 90) for supplying pressurised fluid to the crack-inducing ring (30); characterised in that the crack-inducing ring is not made of metal, and in that the cage further comprises a crack-directing feature (34, 88, 92) on or adjacent the crack-inducing ring and a crack-attracting feature (70, 116) located at the cut-off level (20) outside the crack-inducing ring (30, 96).
2. A pile cage (2) as claimed in claim 1, wherein the crack-inducing ring (30) has a slit or frangible region (32) in a portion of its wall facing towards a centre of the pile.
3. A pile cage (2) as claimed in claim 2, wherein the crack-directing feature comprises fins (34) defining the slit.
4. A pile cage (2) as claimed in claim 1, wherein the crack-inducing ring (30) comprises an annular tube (30) arranged inwardly of the reinforcement structure, the tube having a plurality of apertures in a portion of its wall facing toward the centre of the pile.
5. A pile cage (2) as claimed in any one of the preceding claims, wherein the crack-attracting feature (70, 116) has a dimension of at least a quarter of the depth of cover between the pile exterior and a closest part of the reinforcement structure (4).
6. A pile cage (2) as claimed in any one of the preceding claims, wherein the crack-attracting feature (70, 116) has a dimension of at least half of the depth of cover between the pile exterior and a closest part of the reinforcement structure (4).
7. A pile cage (2) as claimed in any one of the preceding claims, wherein the means (42, 44, 50, 58, 62, 64, 90) for supplying pressurised fluid to the crack-inducing ring (96) comprises a plurality of crack-inducing plates (90) each provided with means for connection to a pressurised fluid supply and the crack-inducing ring comprises a radial flow control shield (96) surrounding the plates (90) to restrict the flow of escaping fluid.
8. An assembly (110) for use in creating a pile cage (2) as claimed in any one of the preceding claims, comprising a planar support frame (112) and a crack-inducing ring (30, 96) not made of metal, the frame (112) having an inner annular member (114) supporting the crack-inducing ring (30, 96), a concentric outer annular member (116) that is or supports the crack-attracting feature, and a plurality of spaced spokes (118) holding the members (114, 116) together.
9. An assembly as claimed in claim 8, wherein the spokes (118) are positioned to fall between reinforcing bars of pile cages having a variable number of equally spaced reinforcing bars.
10. A method of breaking a reinforced concrete pile (100) comprising the steps of placing a fluid-receiving means (30, 90, 96) into a pile cage (2) at a cut-off level (20), protecting an upper part (10) of the pile cage (2) with debonding material (22), casting the pile, and supplying pressurised fluid to the fluid-receiving means (30, 90, 96), characterised in that the fluid-receiving means (30, 90, 96) is adapted to permit fluid to flow substantially inwardly towards a centre of the pile at the cut-off level.
11. A method as claimed in 10, wherein the step of supplying pressurised fluid to the fluid-receiving means comprises use of a pump that enables the application of pressure to be controlled.
Type: Application
Filed: Apr 12, 2005
Publication Date: Sep 20, 2007
Applicant: LAING O'ROURKE PLC (DARTFORD)
Inventor: Philip French (Dartford)
Application Number: 11/578,474
International Classification: E02D 9/00 (20060101);