Method and system for removing a pile from a ground founded location

Abstract

The invention relates to a method for removing a pile from a ground, such as a bedding at an off shore location, wherein the pile has a passage through the pile from an upper end to a bottom end, the bottom end having been inserted into the ground, wherein the passage is closed off using a plug, whereafter a pressure fluid is inserted into the passage below said plug, which pressure fluid is pressurized, such that the pile is pushed out of the ground by at least said pressurized pressure fluid, wherein prior to pushing the pile out of the ground by said pressure fluid a body of a fluid is provided between a periphery of the plug and a periphery of the pile, which body of fluid is cooled, such that the body of fluid freezes, fixating the plug to the pile and closing off said passage with the plug.

Description

[0001] P138986PC00

[0002] Title: Method and system for removing a pile from a ground founded location

[0003] The invention relates to a method for removing a pile from a ground founded location. The invention further relates to a system for removing a pile from a ground founded location.

[0004] Ground founded piles are used for founding structures in fixed position. For example, piles are used at offshore locations for supporting offshore structures, such as for example wind turbine generators (WTG’s), offshore platforms and the like. These piles, also referred to as foundation piles, are generally substantially hollow piles which have a lower end, driven into the ground, for example a water bedding, and an upper end, supporting said structure. At the end of the technical and / or economical life of the structure or of the pile the pile needs to be removed from the ground. This is also referred to as decommissioning of piles.

[0005] It is known to use lifting means such as a crane vessel to pull the pile from a bedding. Since such piles are large, for example having a diameter of several meters to more than ten meters, and a length of tens of meters or more, they are heavy. Moreover there are high frictional forces between the lower end of the pile, driven into the ground, and the ground itself. Thus it requires very large crane vessels to pull the pile from the ground, which makes this complex, time consuming and costly. Moreover pulling a pile from a ground is dangerous because it is hard to predict when the frictional forces will be overcome, meaning that the pile will suddenly move upward, reducing the force required, which may lead to uncontrolled movement or even toppling or capsizing of the crane.

[0006] It has been proposed to decommission piles by closing off an upper end of a pile by welding a closure to the upper end of the pile after removing the top structure, and then filling the passage or void of the pile with water and then pressurizing the water. Surprisingly in tests it has been found thatby pressurizing the water inside the pile the pile is pushed upward, forcing the lower end out of the bedding.

[0007] This so far experimental method has the disadvantage that the closure needs to be manufactured specifically for the pile to be decommissioned. Moreover the closure has to be welded in situ to the upper end of the pile, which to that end has to be prepared for such welding, which is again complex, time consuming and costly, requiring specialist equipment and personnel. Also, every pile needs its dedicated closure since it is hard and costly to re-use this closure several times.

[0008] There is a need for an alternative method for removing a pile from a ground, such as a bedding. There is a need for such method which eliminates or at least reduces the disadvantages of the known methods. There is a need for such method which is safe to use and relatively easy to perform. There is moreover a need for systems for removing a pile. There is a need for such system which eliminates or at least reduces the disadvantages of the known systems. There is a need for such system which is safe to use and relatively easy to operate.

[0009] In an aspect a method for removing a pile can be characterized in that the passage is closed off using a plug, whereafter a pressure fluid is inserted into the passage below said plug, which pressure fluid is pressurized, such that the pile is pushed out of the ground by at least said pressurized pressure fluid. According to the disclosure prior to pushing the pile out of the ground by said pressure fluid a body of a fluid is provided between a periphery of the plug and a periphery of the pile. Said body of fluid is cooled, such that the body of fluid freezes, fixating the plug to the pile and closing off said passage with the plug.

[0010] Surprisingly it has been found that freezing a fluid between the plug and the pile will provide for an appropriate holding force for the plug to withstand the high pressure of the pressure fluid necessary for pushing the pile from the ground. Whereas after use the body of fluid can be allowed tothaw again, releasing the plug from the pile easily. The plug can for example be reused for decommissioning a further pile.

[0011] A method of the disclosure is especially suitable for removing offshore piles.

[0012] In a method of the disclosure preferably the body of fluid is formed by water, especially sea water, and the pressure fluid is water, preferably sea water. Using water for pressurizing and for freezing has the advantage that it is easily available, especially sea water off shore, whereas it will not lead to pollution when spilled and it requires no significant precautionary provisions to avoid such spillage prior to, during or after use. The water can be released into the sea after use, or can easily be removed for discarding elsewhere. By using sea water taken in from the vicinity of the pile to be decommissioned, the water is easily available and can be discarded directly back into the sea.

[0013] In advantageous embodiments the plug is inserted into the passage in said pile, wherein the body of fluid is formed between an outer periphery of the plug and an inner surface of the pile. When freezing the body of fluid will expand radially, providing the force needed for securing the plug to withstand the pressure.

[0014] Preferably the plug is lowered into the passage of the pile so far as it is at least partly submerged into water inside the passage, said water forming the body of fluid to be frozen. Said water can for example be sea water already present inside the passage prior to starting decommissioning, or can be water introduced into the passage on purpose, for example as part of the pressurizing fluid.

[0015] In advantageous embodiments prior to providing the plug to the pile an upper section of the pile is removed, preferably an upper section extending above the water level of the sea or at least any part having a diameter which is smaller than a part in or on which the plug has to be provided. This provides easy access into the pile.The body of fluid is cooled to a temperature below the freezing temperature of said fluid, especially at least 2 degrees Celsius below said freezing temperature, more preferably more than 5 degrees Celsius below said freezing temperature. Sea water will generally freeze at temperatures below about minus 1.9 to 2 degrees Celsius. By lowering the temperature well below said freezing temperature freezing will be accelerated, which is advantageous in view of the time needed for the decommissioning.

[0016] In preferred embodiments prior to providing the plug the relevant surface of the pile against which said body of fluid is to be formed is cleaned, for example to remove algae, animals such as crustaceans and mud, for example by brushing the surface and / or by power washing. This will even better ensure proper forming of a frozen body of fluid closing off and resisting the pressure.

[0017] Preferably the pressure fluid is introduced into the passage through the plug. This has the advantage that no changes have to be made to the pile, other than, if applicable, closing possible openings in the wall of the pile in the area which is to be pressurized.

[0018] During pushing of the pile out of the bedding and thereafter preferably the pile is supported by an external device, such as a crane or vessel. In advantageous embodiments of a method of the disclosure after freezing the body of water, during and / or after pushing the pile out of the ground an external upward force is exerted on the plug for lifting the pile, providing such support, whereas the pile can then also be lifted by such force for further handling.

[0019] It has been found that freezing the body of fluid provides sufficient holding force for the plug to resist the pressure necessary for forcing the pile upward, pushing it from the ground, as well as for lifting the pile.

[0020] Nevertheless it can be advantageous when in embodiments of a method of the disclosure in addition to the freezing of the body of fluid the plug is mechanically connected to the pile too, for example by clamping. This canprovide for a safety measure, should the freezing fail, and / or can aid in holding the plug to the pile.

[0021] The disclosure is further directed to systems for pushing a pile from a ground, such as from a water bedding. In an aspect of the disclosure such system comprises a plug having at least a peripheral wall and a closure closing off a space within said peripheral wall, wherein the plug is designed for cooling at least part of the peripheral wall to a freezing temperature. Such system is especially equipped for use in or for performing a method of the disclosure.

[0022] In embodiments of a system of the disclosure the plug has a peripheral chamber, comprising at least one cooling channel for cooling said at least part of the peripheral wall. In such embodiment the cooling channel can easily be protected from damage, for example when lowering the plug or by pressure exerted by the pressure fluid. Preferably fluid for forming a body of fluid between the plug and the pile can enter into said chamber to be cooled by the cooling channel. To this end for example openings can be provided, extending from said peripheral wall into said chamber.

[0023] In advantageous embodiments the plug comprises an inlet and an outlet to said at least one channel for feeding a coolant through said channel. In such embodiments the coolant can be cooled outside the plug and can be circulated through the channel for freezing. Thus the system used for cooling the coolant need not be subjected to the pressures of the pressure fluid.

[0024] In advantageous embodiments the plug is provided with at least an entry for during use feeding a pressure fluid through said entry into a space below said plug. A fluid line can be connected to said entry for feeding fluid, especially water, more preferably sea water, under pressure into said space, pressurizing said space. The fluid is preferably pumped into the space.Preferably the plug further more is provided with at least one of at least one lifting element for connecting a lifting system to the plug and at least one mechanical device for clamping the plug to a surface of a pile to be pushed.

[0025] In further advantageous embodiments the disclosure is directed to a system comprising a pile mounted with a lower end into the ground, such as a water bedding and a system according to the disclosure for pushing the pile out of the ground.

[0026] In advantageous embodiments in such system the pile has an inner diameter and the plug has an outer diameter, wherein the outer diameter is smaller than the inner diameter, such that the plug can be lowered into the pile, forming an annular space between the plug and the pile, to be filled with a body of fluid to be frozen for forming a solid frozen body filling said annular space. Alternatively the plug can have an inner diameter larger than an outer diameter of the upper end of the pile, such that the plug can be lowered over the pile, forming an annular space between the plug and the pile, to be filled with a body of fluid to be frozen for forming a solid frozen body filling said annular space. The said space preferably has a relatively small width, seen in radial direction of the pile, compared to the diameter of the pile. The width is for example about 0.05 times the diameter or less, for example 0.02 times the diameter or less.

[0027] The invention will be further elucidated on the basis of exemplary embodiments which are represented in the drawings. The exemplary embodiments are given by way of non-limitative illustration of the invention. In the drawings schematically show:

[0028] Fig. 1 a pile founded in a ground, here shown by way of example as a bedding, supporting an offshore structure, part of which is shown;

[0029] Fig. 2, in cross section, a pile as shown in fig. 1, with an upper section and the offshore structure having been removed;

[0030] Fig. 3 the pile of fig 2, being partially cleaned on an inside;Fig. 4 the pile of fig. 3, a plug being lowered into the passage of the pile;

[0031] Fig. 5 the pile of fig. 4, the plug fixed inside the passage of the pile by a frozen body of water;

[0032] Fig. 6 the pile of fig. 5 being pushed out of the bedding;

[0033] Fig. 7 at a larger view in cross section a plug according to the disclosure, inside a pipe;

[0034] Fig. 8 in isometric cross section the plug of fig. 7, inside the pipe; Fig. 9 an alternative embodiment of a plug of fig. 7, in a pipe; and Fig. 10 in cross section further embodiment of a plug of the disclosure, here shown mounted on a pipe.

[0035] In this description embodiments of the invention will be described with reference to the drawings by way of example only. These embodiments should by no means be understood as limiting the scope of the disclosure. At least all combinations of aspects, elements and features of the embodiments shown and discussed are also considered to have been disclosed herein. In this description the same or similar elements and features will be referred to by the same or similar reference signs. The drawings are not to scale, and can show exaggerations in order to more clearly show features of the claimed invention.

[0036] In this description expressions of orientation such as top, bottom, vertical etcetera are used for convenience only and refer to the orientation of the foundation pile as seen in the accompanying drawings, the pile being placed vertically in the bedding. It will be clear that the axis of the pile need not extend vertically

[0037] In this description wording like substantially and generally should be understood as meaning that relatively small deviations from the feature or value they refer to are also considered to be covered, for example deviations of 20% or less, such as 15% or less or 10% or less.In this description by way of example embodiments of off-shore foundation piles are disclosed, the off-shore foundation pile being provided for supporting for example a platform and / or a wind turbine generator (WTG) supported on the foundation pile, directly or indirectly, preferably free of a transition piece. When performing a method of the disclosure and / or using a system, or parts thereof, according to the disclosure any such platform, WTG or the like, with any transition piece if provided, is preferably removed from the foundation pile beforehand. In the same or a similar manner piles can be removed on shore.

[0038] In this description a foundation pile is a pile supported in a ground, such as a bedding of water, for example by driving or otherwise inserting the foundation pile into the ground, such as a water bedding such as a sea bedding, onshore or offshore, also referred to as bedding. The foundation pile is disclosed in the drawings as a monopile, for example made of metal, but could also be a pile made of different segments, and could be made of different materials, such as but not limited to concrete, or combination of materials, such as but not limited to concrete and metal. The foundation pile is substantially hollow, at least over most of its height. A foundation pile can have a circular cross section, seen in top view, perpendicular to a longitudinal axis thereof, as shown by way of example in fig. 1 -6, but could also have a different shape in cross section, for example polygonal, oval or the like, or combinations thereof. A foundation pile, such as an off-shore foundation pile can have a diameter of several meters to more than ten meters, for example up to or above fifteen meters at its lower end, and can have a wall thickness, if made of metal, of centimeters, for example more than 4 centimeters, such as for example 8 to 10 centimeters or more. These sizes are only given by way of example and should not be considered to limit the disclosure. In this description the or an off-shore foundation pile will be referred to as foundation pile and is shown and discussed as a preferred example of a pile.Fig. 1 shows schematically a pile 1, founded in a ground, especially in a bedding 2 of a sea or ocean, further also referred to as bedding or sea bedding 2. The pile 1 has an upper end 3 and a lower end 4. An offshore structure 100 is supported by the upper end 3, for example a tower of a wind turbine generator as shown partially in fig. 1. The pile 1 is hollow, comprising a peripheral wall 5 and a passage 6 extending longitudinally, parallel with the longitudinal axis X - X of the pile 1, between the upper end 3 and the lower end 4. The lower end 4 has been driven into the bedding 2, such that the wall 5 is enclosed by the bedding 2, both at the outside and at the inside of the pile 1. A column 2 A of the bedding extends inside the passage 6. Primarily friction between the bedding 2, 2 A and the wall 5 and the weight of the pile 1 prevent or at least act against pulling the pile 1 upward, out of the bedding 2.

[0039] When the pile 1 needs to be decommissioned or removed from the bedding for other reasons, the lower end 4 has to be removed from the bedding 2. In the present disclosure this is achieved by at least pushing the pile 1 upward, in said longitudinal direction. To this end in methods according to the disclosure the passage 6 is closed off using a plug 7, whereafter a pressure fluid 8 is inserted into the passage below said plug 7. The pressure fluid 8 is pressurized, such that the pile 1 is pushed out of the bedding 2 by at least said pressurized pressure fluid 8. A method according to the disclosure is presented, by way of example, in steps, in fig. 1 -6 for removing an offshore pile. In the same or a similar manner a pile can be removed onshore.. As can be seen in these figures the passage 6 below the plug 7, which is also referred to as pressure space 9, is filled with the fluid 8, such that when pressurizing the fluid 8 for example by feeding additional fluid 8 into said pressure space 9, the fluid 8 will expand the pressure space 9, pushing against the column 2A and the plug 7 and thus provides for an upward pushing force F against the plug 7, pushing the lower end 4 of the pile out of the bedding 2. To this end the plug 7 has to be locked relative tothe pile 1, such that by pushing against the plug 7 the plug will not move significantly, preferably not at all, relative to the pile 1. In fig. 4-9 the plug 7 is provided inside the passage 6, whereas in fig. 10 an alternative embodiment is shown, wherein the plug 7 is mounted over the pile 1, as will be discussed.

[0040] In methods according to the disclosure prior to pushing the pile 1 out of the bedding 2 by said pressure fluid 8 a body of a fluid 10 is provided between a periphery 11 of the plug 7 and a periphery 12 of the pile 1. The body of fluid 10 is cooled, such that the body of fluid 10 freezes, fixating the plug 7 to the pile 1 and closing off said passage 6 with the plug 7. Such plug 7 with a frozen body of fluid 10 is shown for example in fig. 5 - 10

[0041] It has been found that by freezing such annular body of fluid 10 provides holding force by friction between the frozen body of fluid 10 and the wall 5 of the pile 1 to allow the pile 1 to be pushed out of the bedding 2, overcoming the friction between the bedding 2 and the pile 1 and the weight of the pile 1. Moreover the frozen body of fluid 10 has proven to be sufficient for sealing off the annular gap 13 between the plug 7 and the wall 5, resistant against the high pressure of the pressure fluid 8. Whereas by thawing the body of fluid 10 again the plug 7 can easily be released from the pile 1.

[0042] In a method according to the disclosure preferably water is used as a fluid for forming the body of fluid 10. In a method according to the disclosure preferably water is used as a pressure fluid 8. Preferably for both the body of fluid 10 and as pressure fluid 8 water is used. The water used as pressure fluid 8 and / or for forming the body of fluid 10 is preferably sea water, especially when offshore since this is present and available in abundance offshore, and can be returned to the source, especially back into the sea or ocean easily after use. The water can be treated before it is returned into the sea or ocean, for example filtered, in order to even better prevent spoilage and pollution.As can be seen in fig. 4 - 6 in embodiments of methods according to the disclosure the plug 7 is inserted into the passage 6 in said pile 1. In such embodiments preferably the body of fluid 10 is formed between an outer periphery 11 of the plug 7 and an inner surface 12 of the pile 1.

[0043] In methods according to the disclosure preferably prior to providing the plug 7 to the pile 1 the supported structure, such as an offshore structure 100 is removed, as well as an upper section 14 of the pile 1, such as an upper section 14 extending above a water level 15. In fig. 1 a line II -II is shown by way of example of a level at which the upper section 14 can be cut from the pile 1. Fig. 2 - 6 and 1 show the pile 1 with the upper section 14 removed, wherein for ease of reference the remaining part of the pile 1 is still referred to as the pile 1 or foundation pile 1, and the upper end of the remaining part of the pile is further also referred to as upper end 3.

[0044] Moreover, prior to filling the passage 6 with the pressure fluid 8, especially water, more preferably sea water, any opening in the wall 5 of the pile 1 at or below an area where the plug 7 is to be positioned will be closed, for example by welding, plugging, sleeving or any such suitable manner. Thus the pressure space 9 can be properly fluid tight. Furthermore, prior to inserting the plug 7 into the passage 6 the relevant surface 12 of the pile against which said body of fluid 10 is to be formed can be cleaned. In fig. 3 by way of example schematically a brush 16 is shown, lowered into the passage 6, for cleaning such as brushing the inner surface 12 of the pile 1 at a level where the plug 7 is to be placed. Most or all of any contamination on said surface 12 which could prevent proper functioning of the body of fluid 10 can be removed, such as but not limited to algae, animals such as crustaceans, surface rust and the like. Instead of or in addition to a brush 16 other cleaning means can be used, such as but not limited to a power brush, water hose, sanding, milling or the like.

[0045] The body of fluid 10 is cooled to a temperature below the freezing temperature of said fluid for forming the body of fluid 10. For example,when sea water is used for forming said body of fluid 10 the cooling is set such that the sea water temperature is brought at least to below about minus 1.8 to minus 1.9 degrees Celsius, such as for example below minus 2 degrees Celsius, depending on for example salinity of the sea water.

[0046] Preferably the cooling is set such that the temperature of the body of fluid is well below the freezing temperature of said fluid. For example for sea water the temperature can be set to be at least 2 degrees Celsius below said freezing temperature, i.e. set at about minus 3.8 - minus 3.9 degrees Celsius, more preferably more than 5 degrees Celsius below said freezing temperature, i.e. for sea water at about minus 7 degrees Celsius. The lower said temperature the faster the fluid will freeze.

[0047] In preferred embodiments of a method of the disclosure the pressure fluid 8 is introduced into the passage 6 through an entry 17 extending through the plug 7, as schematically shown in fig. 5 - 10. If so desired also an outlet 27 can be provided for removing at least part of the pressure fluid 8 from the pressure space 9, which can also act as a safety release, for example by use of a suitable pressure relief valve.

[0048] Fig. 4 shows a step of lowering the plug 7 into the passage 6 using a suitable lifting device 18. In fig. 3 -6 this lifting device 18 is shown, by way of example, as a floating crane 18, a hoisting cable 19 of the crane 18 connected to the plug 7. Moreover a first line 20 is connected to the plug 7, especially to cooling means such as a cooling channel 21 in said plug 7, examples of which are discussed hereafter, with reference to for example figs. 7 - 10. In embodiments the line 20 comprises both a feeding channel 22 and a return channel 23, which are connected to a feeding side of a cooling device 24, and to a return side of said cooling device 24. In the embodiments shown the cooling device 24, which can be any suitable cooling device 24 or system, can be provided aboard the crane 18, or at a different vessel, or connected to the pile 1 or provided in any other suitable way, and is designed for cooling a coolant circulating through the feeding channel 22,the cooling channel 21, the return channel 23 and the coohng device 24, which preferably form a closed circuit. An appropriate pump can also be provided for pumping the coolant through said circuit.

[0049] As can be seen in fig. 4 also a pressure fluid feed line 25 can be connected to the plug 7 when lowered into the passage 6, especially connected to the inlet 17, for feeding pressure fluid into the pressure space 9. In such embodiments a pump 26 can be provided, for example on the floating crane 18 or a separate vessel or below the water level 13, for example resting on the bedding 2, or any other suitable position which pump is connected to the fluid feed line 25 for pumping fluid 8, 9, especially (sea)water from the body of water surrounding the pile 1, into the pressure space 9. The pump 26 can be any suitable pump 1 as long as the desired pressure for pushing the pile 1 out of the bedding 2 can be obtained. The pressure necessary may vary, for example depending on at least the weight and the dimensions of the pile 1 and the friction experienced between the pile 1 and the bedding 2. The upward force F acting on the plug 7 and frozen body of fluid 10 will equal the pressure P of the pressurized fluid 8 in the pressure space 9 times the frontal surface area A of the plug 7 with the frozen body 10, which surface area will equal H * n * DA2, wherein D is the inside diameter D of the passage 6.

[0050] When the pile 1 is being pushed out of the bedding, as for example shown in fig. 6, it could become unstable. To that end it may be useful to provide for external support of the pile. Moreover, when the pile 1 has been pushed fully out of the bedding 2 it needs to be handled further, for which it has to be engaged by suitable equipment. In embodiments of methods of the disclosure, such as for example but not limited to as shown in fig. 4- 6, after freezing the body of water 10, during and / or after pushing the pile 1 out of the bedding 2 an external upward force can be exerted on the plug 7 for lifting the pile 1.In fig. 4 it is shown that the plug 7 can be lowered into the passage 6 using a crane 18 and a hoisting cable 19. This cable 19 can be released and withdrawn after freezing the body of fluid 10 since then the plug 7 is locked in position relative to the pile 1. However, in embodiments the hoisting cable 19 can stay attached to the plug 7, such that through the crane 18 said vertical lifting force can be provided, in addition to the upward pushing force F acting on the plug 7 during pushing of the pile 1 from the bedding 2 and after such release. In such embodiments preferably the body of fluid 10 is kept frozen during at least part of the further handling after the pile 1 has been released from the bedding 2, for example during placing the pile 1 on a vessel for removal, or during grabbing the pile with other handling means, such as a grabber, other crane, hoisting platform or the like.

[0051] In embodiments of the methods of the disclosure in addition to the freezing of the body of fluid 10 the plug 7 can be mechanically connected to the pile 1 too, for providing additional stability, especially during freezing or thawing of the body of fluid 10 and / or for providing a safety for when the freezing of the body of fluid 10 is somehow interrupted or insufficient, whereas such mechanical means could also be suitable for supporting the weight of the pile 1 after having been removed from the bedding, for example when the freezing of the body of fluid has been stopped.

[0052] Fig. 9 shows schematically an example of an embodiment of a plug 7 of the disclosure with a clamp 30 for clamping the plug mechanically to the surface 12 of the passage 6. In this embodiment the clamp 30 comprises two or more arms 31 which can be forced radially outward from a center 32, for example hydraulically, electrically, magnetically or mechanically, for clamping the inside surface 12 of the passage 6. The clamp 30 can also be designed differently, for example with pivoting arms like a claw anchor, engaging when being pulled. The clamp can be connected to one of or both of the plug 7 and the hoisting cable 19.In a pile 1 to be decommissioned or otherwise removed from a bedding 2 the passage 6 regularly will be filled with sea water, even during normal use. If the passage is filled with sea water, as for example shown in fig. 3 - 6, the plug 7 can in embodiments be lowered into the passage 6 so far as it is at least partly and preferably entirely submerged into the water inside the passage 6, said water also forming the body of fluid 10 to be frozen. Should the passage 6 be substantially dry after removal of the top section 12, it can be filled actively, for example prior to or during lowering the plug 7.

[0053] As discussed the disclosure is inter aha related to a system for pushing a pile 1 from a water bedding 2, said system comprising a plug 7. The plug has least a peripheral wall 11 and a closure 33 closing off a space 34 within said peripheral wall 11. The plug is designed for cooling at least part of the peripheral wall 11 to a freezing temperature, as discussed before. Fig. 7 - 10 show, at a larger scale, embodiments of such plug, by way of example and by no means limiting the scope of the disclosure.

[0054] Fig. 7 and 8 schematically show, in cross sectional side view and isometric cross section, an embodiment of a plug 7 inside a passage 6 of a pile 1. In this embodiment the peripheral wall 11 is substantially cylindrical and is at the top end connected to or integral with the closure 33, here shown as a dome shaped roof 35. Inside the peripheral wall 11 the plug 7 has a peripheral chamber 36. In said chamber 36 at least one cooling channel 21 for cooling at least part of the peripheral wall 11. In embodiments the or each cooling channel 21 can be or comprise one or more spirals, fins, blades or the like for increasing the cooling surface. The or each cooling channel 21 is connected to the feeding channel 22 and the return channel 23, such that coolant can be circulated through the channel or channels 21, cooling at least the chamber 36 and / or the peripheral wall 11.

[0055] As is shown in fig. 7 openings 37 extend through said peripheral wall 11 into said chamber 36. Thus fluid, especially water such as sea watercan flow into and out of the chamber 36, passing along the or each cooling channel 21, to be cooled to below the freezing temperature. The peripheral wall 11 protects the cooling channel(s) 21 whereas the body of fluid 10 freezing in the annular gap 13 will force against the peripheral wall 11 as well as against the inner surface 12 of the pile 1. The chamber 36 has the further advantage that it reinforces the peripheral wall 11.

[0056] As shown in fig. 7, 8 and 9, an inlet 38 and an outlet 39 to said at least one cooling channel 21 are provided in the plug 7, especially in the roof 35, for feeding the coolant through said channel 21. The feeding channel 22 and the return channel 23 are connected to or form said inlet 38 and the outlet 39 respectively.

[0057] As discussed before, in embodiments the plug 7 is provided with at least an entry 17 for during use feeding the pressure fluid 8, especially water such as sea water through said entry 17 into a pressure space 9 below said plug 7. The pressure fluid feed line 25 as discussed can be connected to or form the entry 17.

[0058] In embodiments the plug comprises at least one lifting element 40 for connecting a lifting system to the plug 7, such as for example the hoisting cable 19 as discussed. The lifting element 40 can for example be an eyelet, ring, gripper or the like known, suitable devices for attaching for example a line, chain, rod or the like.

[0059] Fig. 9 schematically shows a plug as shown in fig. 7, but provided with at least one mechanical device 30, such as a clamp as discussed previously, for clamping the plug 7 to a surface 12 of a pile 1 to be pushed. As shown in this embodiment, shown by way of example only, the clamp 30 comprises a central portion 32, from which at least two and for example three or more arms 31 extend, which can be forced outward radially and / or tangentially by means of the central portion 32, for example hydraulically, electrically, mechanically or magnetically, for being pushed against the inner surface 12.It will be clear that the plug 7 can be positioned at any longitudinal position in the passage 6, for example relatively close to the upper end 3 of the (remaining part of the) pile 1, or relatively close to the bottom end 4, as schematically shown in fig. 8, or somewhere in between.

[0060] Using a pressure fluid 8 such as water, especially sea water, has the advantage over using a gas like air in that it is virtually non-compressible. Hence once the pile 1 starts moving upward due to the pressure exerted by the pressure fluid 8, the pressure inside the pressure space 9 will immediately drop, unless more pressure fluid is forced into said pressure space, which means that uncontrolled movement of the pile 1 will be avoided. Whereas with gas as a pressure fluid this will be compressed, meaning that if the holding force exerted by the bedding on the pile reduces, because the pile starts moving, the compressed gas will expand, which can lead to uncontrollably forcing the pile upward. Moreover a far larger volume of gas would be necessary to push the pile upward than a volume of water as discussed here before than the volume of fluid necessary. Nevertheless, gas could be used as a pressure fluid or at least part of a pressure fluid.

[0061] Fig. 10 schematically shows an alternative embodiment of a plug 7 according to the disclosure, mounted to the top end 3 of (a remaining part of) the pile 1, wherein the plug 7 is to a large extent similar to that as shown in fig. 7- 9. However, in this embodiment the plug 7 is oversized, such that the upper end 3 of the pile 1 can be fitted inside the space 34 in the plug 7, the chamber 36 with the cooling channel 21 extending alongside an outer peripheral portion 12A of the pile. In this embodiment the peripheral wall 11 of the plug primarily being cooled faces inward of the chamber, towards the pile surface 12A. Between said peripheral wall 11 and the surface 12 the gap 13 is formed in which the body of fluid 10 is to be provided, for freezing by the cooling channel(s) 21. Again openings 37 can be provided in the wall 11 for allowing flow of fluid into and out of the chamber 36. A seal 42 is provided between the lower side of the peripheral wall 11 and the surface12A of the pile 1, closing off said gap 13 to the environment. The seal 42 can for example be a passive seal, such as a plastic or rubber seal closing off by compression and / or deformation and / or friction, or the seal 42 can be an active seal, for example a seal which can be filled with a fluid, such as water or gas, for increasing its volume for closing off said annular gap 13.

[0062] After closing the gap 13 the annular space 43 between the peripheral wall 11 and the surface 12A can be filled with a fluid for forming the body of fluid 10. This fluid can for example be water and preferably is sea water, which can be pumped directly into said space 43. Alternatively the passage 6 of the pile 1 can be filled with sea water to the extent that it flows over the upper end 3 of the pile 1 into the space 43. Either way, after filling said space 43 the fluid, especially water contained therein will be frozen, locking the plug 7 to the pile and closing off the passage, such that it can be pressurized for pushing the pile 1 from the bedding 2.

[0063] In the embodiments shown the cooling is obtained by a coolant flowing though one or more cooling channels, the coolant being cooled external to the plug 7, by cooling device 24. However, in embodiments a cooling device 24 could also be provided in or on the plug 7. Also alternatively or additionally other types of cooling could be used, for example direct cooling of the wall, Peltier elements, liquid nitrogen or other cooling means known in the art of cooling.

[0064] As shown in the drawings and described here before, in advantageous embodiments the pile 1 has an inner diameter D and the plug has an outer diameter D7, wherein the outer diameter D7 is smaller than the inner diameter D, such that the plug 7 can be lowered into the pile 1, especially into the passage 6, forming the annular gap 13 between the plug 7 and the pile 1. Said gap 13 is to be filled with a body of fluid 10 to be frozen for forming a solid frozen body filling said annular gap 13, locking the plug 7 in position inside the passage 6. The gap 13 preferably has a width W in radial direction which is small relative to the diameter D, D7 of thepassage 6 and the plug 7. For example the width W is less than l / 20thof the inner diameter D, such as for example less than l / 40th. In embodiments the with W can be l / 50thor less, for example l / 75thor l / 100thor less of the inner diameter D. The width W is preferably chosen such that the body of fluid 10 inside the gap 13 can be frozen relatively quickly, for example in a time frame of less than a day, especially less than half a day, preferably within hours, such as but not limited to within four hours or less.

[0065] The invention is by no means limited to the exemplary embodiments shown in the drawings and discussed. Many adaptations and alternatives are possible within the ambit of the claims.

[0066] For example the pile can be made differently, for example not as a monopile made of steel, but as a pile made of other materials, such as concrete, or made differently, for example assembled from sections, as long as the sections to be pushed out are connected to each other sufficiently strong and liquid tight to withstand the pressure. The inlet of the pressure fluid can be provided differently, for example through the wall of the pile. A plug as for example shown in fig. 10 can further be provided with a similar chamber with cooling channel along an inside surface 12 of the pile 1, such that a frozen body of fluid 10 can be formed on both sides of the wall, for increasing clamping forces. A cover could be provided inside the passage, on the bedding or column 2A inside the pile for covering the column in order to better prevent blow out of material of the column when pressurizing the fluid. Pushing the pile out of the bedding could be supported by for example vibrating of the pile or otherwise mechanically handling the pile, such as for example by rotation around the axis X - X in order to lower friction and suction between the bedding and the pile. In the drawings a single foundation pile is shown. However, the same methods and systems could be used for pushing other piles from a bedding, and / or for simultaneously pushing multiple piles from a bedding, for example two, three or more piles, such as foundation piles or legs of a platform.

Claims

Claims1. Method for removing a pile from a ground, such as a bedding at an off shore location, wherein the pile has a passage through the pile from an upper end to a bottom end, the bottom end having been inserted into the ground, wherein the passage is closed off using a plug, whereafter a pressure fluid is inserted into the passage below said plug, which pressure fluid is pressurized, such that the pile is pushed out of the ground by at least said pressurized pressure fluid, wherein prior to pushing the pile out of the ground by said pressure fluid a body of a fluid is provided between a periphery of the plug and a periphery of the pile, which body of fluid is cooled, such that the body of fluid freezes, fixating the plug to the pile and closing off said passage with the plug.

2. Method according to claim 1, wherein the body of fluid is formed by water, especially sea water, and the pressure fluid is water, preferably sea water.

3. Method according to claim 1 or 2, wherein the plug is inserted into the passage in said pile, wherein the body of fluid is formed between an outer periphery of the plug and an inner surface of the pile.

4. Method according to any one of the preceding claims, wherein prior to providing the plug to the pile an upper section of the pile is removed, preferably an upper section extending above a water level.

5. Method according to any one of the preceding claims, wherein the body of fluid is cooled to a temperature below the freezing temperature of said fluid, especially at least 2 degrees Celsius below said freezing temperature, more preferably more than 5 degrees Celsius below said freezing temperature.

6. Method according to any one of the preceding claims, wherein prior to providing the plug the relevant surface of the pile against which said body of fluid is to be formed is cleaned.

7. Method according to any one of the preceding claims, wherein the pressure fluid is introduced into the passage through the plug.

8. Method according to any one of the preceding claims, wherein after freezing the body of water, during and / or after pushing the pile out of the ground an external upward force is exerted on the plug for lifting the pile.

9. Method according to any one of the preceding claims, wherein in addition to the freezing of the body of fluid the plug is mechanically connected to the pile.

10. Method according to any one of the preceding claims, wherein the plug is lowered into the passage so far as it is at least partly submerged into water inside the passage, said water forming the body of fluid to be frozen.

11. Method according to any of one of claims 1 - 9, wherein the plug is mounted on top of the pile.

12. System for pushing a pile from a water bedding, comprising a plug having at least a peripheral wall and a closure closing off a space within said peripheral wall, wherein the plug is designed for cooling at least part of the peripheral wall to a freezing temperature.

13. System according to claim 12, wherein the plug has a peripheral chamber, comprising at least one cooling channel for cooling said at least part of the peripheral wall.

14. System according to claim 13, wherein openings extend from said peripheral wall into said chamber.

15. System according to any one of claims 13 or 14, wherein the plug comprises an inlet and an outlet to said at least one channel for feeding a coolant through said channel.

16. System according to any one of claims 12 - 15, wherein the closure is or comprises a dome shaped roof of said plug.

17. System according to any one of claims 12 - 16, wherein the plug is provided with at least an entry for during use feeding a pressure fluid through said entry into a space below said plug.

18. System according to any one of claims 12 - 17, wherein the plug comprises at least one lifting element for connecting a lifting system to the plug.

19. System according to any one of claims 12 - 18, wherein the plug comprises at least one mechanical device for clamping the plug to a surface of a pile to be pushed.

20. System according to any one of claims 12 - 19, wherein the system further comprises a cooling system for cooling a coolant to a freezing temperature and feeding said coolant to and from the plug.

21. System according to any one of claims 12 - 20, wherein the plug is designed to be lowered in to a passage of a pile or over an upper end of a pile.

22. System comprising a pile mounted with a lower end into a water bedding and a system according to any one of claims 12 - 20.

23. System according to claim 22, wherein the pile has an inner diameter and the plug has an outer diameter, wherein the outer diameter is smaller than the inner diameter, such that the plug can be lowered into the pile, forming an annular space between the plug and the pile, to be filled with a body of fluid to be frozen for forming a solid frozen body filling said annular space.

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