NL2013578B1 - A method for removing a solid object out of the ground using pressurized injection. - Google Patents

Abstract

A method for removing a solid object, in particular a solid foundation pile 1, from out of the ground 2, comprises the steps of connecting a hoisting organ to the object, providing a hoisting installation, having the hoisting installation exert an upwardly directed pulling force upon the object, drilling a flow channel 24, injecting a pressurized fluid via the flow channel to underneath a closed bottom end 10 of the object, and lifting the object out of the ground by having the pressurized fluid exert an upwardly directed pushing force upon the object, while at the same time having the hoisting installation exert the upwardly directed pulling force upon the object. The drilling of the flow channel is preferably performed vertically downwards through the solid object including through its bottom end, in particular by means of a sonic drill.

Description

Title: A method for removing a solid object out of the ground using pressurized injection.

The invention relates to a method for removing solid objects out of the ground, on land or offshore, in particular large elongate objects, like foundation piles which may have lengths of more than tens of meters and diameters of more than a few meters.

Sometimes it is desired to have such objects removed from the ground, for example because it is desired to re-use a site for other purposes, or because those objects need to be replaced by new ones.

At present it is known to remove solid foundation piles out of the ground by using a crane or the like, with which the entire foundation pile can be pulled out of the ground. Depending on the length, diameter, material and weight of the pile, as well as the amount of stick and friction between the pile shaft and the ground, this may require very large pulling forces and thus may make it necessary to use truly big heavy cranes. This is particularly the case when long and heavy solid foundation piles need to be removed, for example foundation piles that have a strengthened concrete core and that have lengths of tens of meters and diameters of up to several meters. Such foundation piles then weigh several hundreds of tons, and pulling them out of the ground sometimes even might appear impossible. Also it may lead to the pile breaking in two pieces, with a lower part of the pile remaining behind in the ground. The risk for such breaking may particularly be high when relative old objects need to be removed of which the condition can be assumed to be poor.

In the case of offshore objects which need to be removed, the circumstances may even be harder. For example it may be impossible or way too expensive to sail a big heavy crane vessel to the location where the object needs to be removed.

At present it is also known to remove old foundation piles by demolishing them top down and in some cases leave the lower pile parts behind in the ground. This however is not environmental friendly and introduces a risk for the surrounding areas. In the case of removal of offshore foundation piles standing near a quay wall or the like, it may even lead to a serious destabilization of such a quay wall or the like. Furthermore, in the case of offshore piles needing to be removed, those piles need to be demolished to a level that is at least lower than an aimed new level at which the water bed in the future is aimed to be dredged. Also debris may then fall into the sea bed and contaminate the soil to be dredged. This contamination at least needs to be removed prior to dredging, which shall be very difficult because of lack of sight underwater. The risk of debris staying behind in such cases is significant. Further it is noted that before being able to start demolishing old foundation piles, it may be necessary to first dig away most of the ground around the pile, which is time- consuming and expensive. In the case of removal of offshore foundation piles, this then even would require the making of a dry working dock around the pile, which is also time-consuming and expensive.

It is noted that for the removal of hollow steel foundation piles both on land as well as offshore it is known to make use of fluid pressure in such a way that a crane only has to take away the weight of the pile, whereas the fluid pressure causes the pile to be driven out of the ground.

Such a method on land for example is known from GB 2 450 339, which shows a removal of a hollow steel foundation pile that extends with a lower part into the ground and with an upper part above the ground. For this a lid gets fixedly connected on top of the hollow pile such that it fully closes of the hollow space inside the pile in the upwards direction. In the downwards direction this hollow space is delimited by ground with which the lower pile part has filled itself during its driving into the ground. Lifting points have been welded to the upper pile part. During removal, a feeding device for pressurized water gets connected to the pile such that pressurized water is fed into the hollow space inside the upper pile part. The pile then on the one hand can get pulled upwards by means of a crane that exerts an upwardly directed pulling force to the lifting points, while on the other hand the pressurized water builds up a pressure in between the lid and the ground, and thus exerts an upwardly directed pushing force onto the pile. Together these forces may drive the pile from the ground.

However a disadvantage here is that this method can only be used for hollow piles and is unsuitable for a removal of solid objects. Another disadvantage is that it has appeared that the crane still has to exert considerable pulling forces onto the pile, particularly in the case of long piles with relative large diameters. Another disadvantage is that the entire pressure-induced pushing forces need to be transferred from the lid towards the pile. This may lead to dangerous situations, in which the lid may get blown of the pile should the forces become too high. Also it has appeared that it is rather unpredictable how the ground behaves during and after the removal of the pile. A space may be left behind in the ground or not, and this space may even comprise closed-in voids because of the ground leaving the pile’s interior plug wise and/or at a late stage. A similar method as the one described in GB 2 450 339, is disclosed for offshore circumstances in US 7,090,434. Here substantially the same disadvantages go as for GB 2 450 339.

The present invention aims to at least partly overcome the abovementioned disadvantages, or to provide a usable alternative. In particular the invention aims to provide a user-friendly method for a quick and easy removal of solid objects, in particular foundation piles, out of the ground, against relative low costs without disturbing the environment with too much noise or pollution.

This aim is achieved by a method according to claim 1. The method comprises the steps of connecting a hoisting organ to the solid object, providing a hoisting installation, and having the hoisting installation exert an upwardly directed pulling force upon the solid object. According to the inventive thought the method further comprise the step of drilling a flow channel either into the ground either into the solid object, to a position underneath a closed bottom end of the solid object. Subsequently a pressurized fluid gets injected via the flow channel to underneath this closed bottom end of the object. The object is then lifted out of the ground by on the one hand having the pressurized fluid exert an upwardly directed pushing force upon the object, while on the other hand at the same time having the hoisting installation exert the upwardly directed pulling force upon the object. The entire solid object together with the surrounding ground as it were start to act as a hydraulic piston-cylinder system. The hoisting installation and injection of pressurized fluid will work together to create at least enough lifting capacity to break adhesive forces between the object and the ground.

This advantageously makes it possible to use a relative light hoisting installation. For example the hoisting installation only needs to carry the weight of the solid object, whereas the pushing forces induced by the injection of the pressurized fluid serve to deal with all the other forces that try to keep the object in place. For example it may help to reduce or overcome the abovementioned adhesive sticking forces between the object and the ground. Owing to the invention, the injection of the pressurized fluid, also has the positive effect that the pore water pressure of the surrounding soil underneath the bottom end remains to lie above the hydrostatic pressure at that location. Thus the injection of the pressurized fluid prevents that a counteracting suction force gets formed underneath the bottom end of the object. Such a suction force would otherwise suck the bottom end of the object back down again when trying to lift it upwards out of the ground. The forces induced by the injection of the pressurized fluid underneath the closed bottom end of the object, truly get to exert pushing forces on the closed bottom end of the solid object. Thus there is no risk of those pushing forces getting to blow parts of the object forcedly away in the direction of workers or the like. Furthermore, the risk of the object getting pulled in pieces is substantially lowered owing to the reduced pulling forces that are to be exerted by the hoisting installation. The object can be removed from out of the ground in its entirety without leaving any parts thereof behind. This makes the method safe and environmentally friendly. The method can be performed quick and against relative low costs. Also the noise level of the method can be kept low. Also it is noticed that the surroundings of the object location do not run a risk of getting negatively disturbed, because a space that is left behind in the ground by the object, automatically and immediately gets filled up with the injected fluid. Thus the likelihood of landslides and/or subsidence is minimized.

The objects to be removed with the invention can be all kinds of objects. Important is that they are solid objects that comprise a closed bottom end. With solid it is meant that the object does not have an open or hollow structure. In particular the object is substantially made out of or filled with a core material which forms an integral part of it. More in particular the object comprises a concrete core possibly reinforced/strengthened with metal or the like.

Advantageously the invention is used for the removal of foundation piles out of the ground, in particular old vulnerable solid foundation piles of which the strength and integrity leaves to be desired. For example the invention can be used to remove old concrete offshore foundation piles that up till now have served fora (floating) dock jetty. Such concrete foundation piles may have total lengths of tens of meters, diameters of several meters, and thus have total weights of hundreds of tons. Those concrete foundation piles then may stand with a lower part of more than ten meters into the ground, whereas an upper part of the piles extends through the water till above sea level. Even for such large and heavy, old and vulnerable foundation piles it is expected that the invention shall be more than able to get them removed without having to demolish them, without needing an expensive large heavy crane vessel, and without first having to build a dry-dock around them.

The flow channel can be drilled in various manners. For example it can be drilled through the ground just sideways of the object by means of a steered drilling to a position underneath the bottom end of the object.

In a preferred embodiment however, the drilling of the flow channel can be performed vertically downwards through the solid object itself including through its bottom end. Thus the outlet opening of the flow channel can get accurately positioned and end directly below the bottom end of the object, that is to say there where the upwards pushing force is needed during the actual removal step. Despite the fact that the material of the object might be substantially harder than that of the ground near the object, this has the advantage that the drilling process can be more accurately predicted since the material characteristics of the object are known, whereas the ones of the ground and in particular of obstacles that may lie at various depths in the ground are fully unknown.

In a further preferred embodiment the drilling of the flow channel is performed by means of a sonic drill which is driven in rotation while it also incorporates the use of high frequency vibrations to facilitate the drilling process. In particular sonic frequency vibrations are incorporated of more than 100 Hz or 6000 VPM, more in particular sonic frequency vibrations of equal to or more than 150 Hz or 9000 VPM. Surprisingly it has appeared that such a sonic drill can be used for accurately drilling the flow channel through the solid object at high drilling velocity. A high accuracy then has even appeared to be obtainable over drilling distances through the solid object material of tens of meters, also when the solid object was made of relative hard material like reinforced concrete. By having the sonic drill hung freely movable to a lower end of a drill rod of a drilling engine which gets guided along a vertically positioned guide frame, it has appeared that the rotating sonic drill drills/hammers itself with its sonic frequency through the solid object material in the vertical direction. In fact even over lengths of the abovementioned tens of meters, only minor deviations of a few centimetres relative to the vertical are to be expected.

The sonic drill and in particular its guide frame advantageously can get positioned by the same hoisting installation that later on is used for exerting the upwardly directed pulling force upon the object. Of course a distinctive drilling installation can also be used.

In a particular embodiment the method further comprises the step of drilling one or more anchoring holes into the object. Subsequently one or more reinforcement bars, like metal rods, can be placed into those holes, with upper free ends projecting to above an upper end of the object. Those reinforcement bars then can get fixedly casted/cemented, for example grouted, into the holes. The reinforcement bars have the important advantage that they may help to strengthen the object. This may particularly be important when objects need to be removed of which the strength and/or condition is poor. The upper free ends of the reinforcement bars can get connected to a hoisting organ.

The drilling of the one or more anchoring holes can be performed by means of the same sonic drill as is used for the drilling of the flow channel, and preferably are given a same thickness. In the case of a large number of holes that need to be drilled besides the flow channel, use can be made of a suitable template which guarantees an aimed pattern.

The one or more anchoring holes preferably get drilled vertically downwards through the object to a depth just above the bottom end. Owing to this the pressurized fluid that gets injected underneath the bottom end then cannot try to escape via the anchoring holes or begin to exert an upward pushing force onto the reinforcement bars. In the alternative the anchoring holes can also be drilled through the entire object including through its bottom end because the casting/cementing operation suitably closes them off again.

In an embodiment the pressurized fluid that is injected via the flow channel to underneath the bottom end of the object has a density and viscosity higher than water. This has the advantage that the fluid is less able to escape via the surrounding soil, and thus gets to exert its maximum pressure capacity onto the object for helping to lift it out of the ground.

The pressurized fluid can have all kinds of compositions, and for example may comprise a slurry mixture of water and bentonite. Depending on the circumstances it is also possible to use water as main component of the pressurized fluid, in particularly during the beginning of an injection, because then the water may help to flush clean more surface area underneath the bottom end of the object and thus create higher pressing forces.

Preferably the pressurized fluid not only is able to exert an upwards directed pushing force onto the object, but also may be used as a stabilizing compound for filling up space that is left behind in the ground by the object during its lifting. As mentioned above this helps to prevent that space that is left behind in the ground after the object is removed therefrom, may start to collapse. If desired this stabilizing compound then can be replaced again by a suitable filling medium, preferably by natural materials like sand and/or clay with similar characteristics as the surrounding soil. In the alternative it is also possible to immediately use a pressurized fluid that will automatically harden equal to or stiffer than the surrounding soil. In addition thereto or in yet another alternative it is also possible to use a stabilizing compound and/or replacement filling medium, like concrete, that is able to form a new object, like a foundation pile, in the ground after hardening.

In a variant the replacement filling medium may get fed to underneath the bottom end of the object already during its upward lifting movement out of the ground. For this a second flow channel can be provided, preferably drilled through the object itself including through its bottom end. The first flow channel then gets used for the injection of the pressurized fluid, whereas the second flow channel gets used for feeding of the filling medium.

Further preferred embodiments are stated in the subclaims.

The invention also relates to an installation for performing the method.

The invention shall be explained in more detail below with reference to the accompanying drawings, in which: - Fig. 1 shows a schematic view of a drilling step during a removal method according to the invention of an offshore foundation pile; - Fig. 2 shows a drilling template used for the drilling in fig. 1; - Fig. 3 shows a cross sectional view of the pile with respective anchoring holes and a flow channel drilled therein in accordance with the template; - Fig. 3a shows an enlarged detail view of an upper end of the pile of fig. 3; - Fig. 4, 4a are views according to fig. 3, 3a which show the placing and casting of reinforcement bars; - Fig. 5, 5a are views according to fig. 3, 3a which show the placement of a top plate and grouting of the upper pile end; - Fig. 6, 6a are views according to fig. 3, 3a which show the placement of a hoisting organ; - Fig. 7, 7a are views according to fig. 3, 3a which show the injecting of a pressurized fluid via the flow channel to underneath a bottom end of the pile; and - Fig. 8, 8a are views according to fig. 3, 3a which show the upward lifting of the pile out of the ground.

In fig. 1 a foundation pile has been indicated with the reference numeral 1. The pile 1 comprises a steel shell with a concrete core. The pile 1 has a total length of more than twenty metres, has a lower pile part T that extends a few metres into the ground 2 of a sea bottom, and an upper pile part 1” that extends a few metres through the water 3 till above sea level 4. The diameter of the pile 1 is more than two metres, whereas the lower pile part 1’ here has a larger diameter than the upper pile part 1” for stability reasons.

The pile 1 together with other similar piles has served for many years as a foundation for a floating dock deck near a quay. This floating dock in fig. 1 can no longer be seen since it has already been dismounted. The dock is now no longer necessary, amongst others because the piles could no longer be fully trusted. It is now desired to have the foundation piles 1 removed without leaving any remainders behind and without disturbing the ground tensions such that the quay remains unharmed.

As a first step for this removal a number of anchoring holes 5 are drilled from above in the vertical direction into the concrete pile 1 over substantially its entire length. For this a drilling template 7 with a number of predefined openings 8 lying at a circle is used, which can be seen in fig. 2, and which gets placed on top of the pile 1.

Each anchoring hole 5 is drilled to a depth just above a closed bottom end 10 of the pile 1, in particular a few centimetres there above. The drilling takes place with the aid of a sonic drill installation. This sonic drill installation comprises a drilling engine 13 that is designed to drive a drill rod 14 in rotation and at a sonic vibrating frequency. At the end of the drill rod 14 a sonic drill head is freely movably mounted. This drill head can for example be formed by a metal cylinder having a diameter of between 50-100 mm, that is equipped with a hardened drilling edge and a number of hardened drilling points at the outer circumference, for example made out of tungsten carbide. The drilling engine 13 is movably guided by a vertical guide frame 15 that is positioned above the pile 1 by a crane 17 that is placed on top of a vessel 18 that has been anchored near the pile 1. Thus the drilling head is able to make a vertical downward movement at least equal to the length of the pile 1 and thus drill itself through the concrete material of the pile 1 while hammering upon it at the sonic frequency. A temporary working platform 20 has been mounted on top of the pile 1, to which access is possible via a barge 21. Thus workman are able to accurately guide and assist the drill head towards the aimed opening 8 in the template 7 at the start of a drilling process.

Besides the anchoring holes 5, a flow channel 24 is drilled from above in the vertical direction through the concrete pile 1 over its entire length including through its closed bottom end 10. This flow channel 24 lies at a central position in between the anchoring holes 5 in accordance with a central opening 25 in the drilling template 7. The drilling of the flow channel 24 takes place with the same sonic drill installation.

As soon as all the anchoring holes 5 and the flow channel 24 have been drilled, the drilling installation is removed and for example placed aside on the vessel 18 by the crane 17.

As a second step, which is shown in fig. 4, reinforcement bars 27 with diameters somewhat smaller than the drilled anchoring holes 5, are placed in each of the anchoring holes 5. Each reinforcement bar 27 has a length that is somewhat larger than the length of the pile 1, such that free ends 27’ of the bars 27 get to project above an upper end 28 of the pile 1. The positioning and lowering of the bars 27 into the holes 5 can be done with the crane 17. A cementing material, like grout, has been casted into the anchoring holes 5 such that after hardening a fixed connection is obtained between the bars 27 and the pile 1. The bars 27 then can be used as lifting organs. For this they are individually tested with the aid of a hydraulic jack to ensure their bearing capacity.

As a third step, which is shown in fig. 5, the upper end 28 of the pile 1 gets smoothly grouted and gets a top plate 30 placed there upon.

As a fourth step, which is shown in fig. 6, a metal hoisting organ 32 gets placed on top of the plate 30 and gets bolted to the reinforcement bars 27. This hoisting organ 32 than gets connected to a hoisting cable 33 of the crane 17 and gets pre-tensioned.

As a fifth step, which is shown in fig. 7, a pressurized fluid 34 gets injected via a hose 35 into the flow channel 24. For this the hose 35 on one side is connected to a pump 36 (that is stored on the vessel 18 and there connects to a reservoir), and on its other side is connected to the flow channel 24 via a suitable intermediate connection thereof with the hoisting organ 32. The pump 36 then starts to inject the pressurized fluid 34 underneath the bottom end 10 of the pile 1. This creates a lifting pressure P, since the fluid has been chosen such uncompressible and/or thick that is at least partly unable to penetrate into the ground 2. The pile 1 will act as a hydraulic piston.

As a sixth step, which is shown in fig. 8, the crane 17 starts to exert an upwardly directed pulling force F on the pile 1. The crane 17 and the pump 36 then will work together to create enough lifting capacity to break the adhesive sticking forces between the pile 1 and the ground 2, while at the same time the injection of the fluid 34 prevents that a vacuum gets drawn underneath the bottom end 10 of the pile 1. The crane 17 preferably will gradually increase its pulling force until it reaches the weight of the pile 1. When the adhesive strength has been broken, the pile 1 shall start to move upwards out of the ground 2. During this upward hoisting of the pile 1, the fluid 34 remains to get injected with enough capacity underneath the bottom end 10 of the pile 1 to keep up with the lifting speed of the pile 1.

This will take place with a slight overpressure of the fluid 34 in order to guarantee stability of the soil around a hole 40 that is left behind in the ground.

The fluid 34 that gets injected via the flow channel 24 here is formed by a curable stabilizing compound that overtime becomes harder than the surrounding soil. When the bottom end 10 of the pile 1 has reached a future dredging level for the sea bottom, the pumping of curable compound will be stopped and switched to water.

After the entire pile 1 is retracted, it will be lowered on a demolition barge. After that the procedure is repeated for another pile.

Besides the embodiment shown, numerous variants are possible. For example other types of drill equipment can be used. Also it is possible to use other types of hoisting organs, for example one that gets clamped around the upper pipe end. If desired, for example in case the pile has more frictional force/resistance than expected, it is possible to provide an additional lifting tool. For example a horizontal lifting beam can be slid into the hoisting organ while also getting connected to the vessel. By subsequently de-ballasting the vessel, an additional vertical reaction force acting upon the hoisting organ and thus onto the pile can be generated. With this use can even be made of the tide.

Thus the invention provides an innovative removal method for large solid objects out of the ground that makes use of a combination of lifting forces such that the object is able to remain intact (with the exception of the channel and/or holes drilled into it) during its entire removal.

Claims (14)

A method for removing a solid object, in particular a solid foundation pile, from the ground, comprising the steps of: connecting a hoisting member to the object; the provision of a hoisting installation; and allowing the hoisting installation to exert an upwardly directed tensile force on the object, characterized in that the method further comprises the steps of: drilling a flow channel; injecting a pressurized fluid through the flow channel to a closed bottom end of the object; and causing the object to rise from the ground by causing the pressurized fluid to exert an upwardly directed compressive force on the object, while at the same time the hoisting installation exerts the upwardly directed tensile force on the object. A method according to claim 1, wherein the drilling of the flow channel is performed vertically downwards through the solid object including through its bottom end. A method according to claim 2, wherein the drilling of the flow channel is performed by means of a sonic drill at a sonic vibration frequency. A method according to any of the preceding claims, further comprising the steps of: drilling one or more anchor holes in the object; placing one or more reinforcing bars in the holes; securely connecting the reinforcing bars in the holes with a binder; and connecting the reinforcing bars with the hoist. A method according to claim 4, wherein the drilling of the one or more anchor holes is carried out by means of a sonic drill at a sonic vibration frequency. A method according to claim 4 or 5, wherein the one or more anchor holes are drilled vertically down through the object to a depth just above the bottom end. A method according to any of the preceding claims, wherein the pressurized fluid injected through the flow channel below the bottom end of the object has a density and viscosity that is greater than that of water. A method according to any one of the preceding claims, wherein the pressurized fluid comprises bentonite. A method according to any of the preceding claims, wherein the pressurized fluid is a stabilizing mixture that will cure equal to or harder than the soil. A method according to any of the preceding claims, wherein the solid object has an elongated shape. A method according to any of the preceding claims, wherein the solid object has a cylindrical shape. A method according to any of the preceding claims, wherein the solid object comprises a concrete core, in particular a reinforced concrete core. A method according to any of the preceding claims, wherein the solid object is an offshore foundation pile that is partially placed in the seabed. An installation for carrying out the method according to one of the preceding claims.