Patent Application
20160160467
The invention relates to a pile-driver, and more particularly to a pile-driver suitable for offshore operations.
In addition, the invention relates to a method for driving a pile downward into the ground using such a pile-driver.
Drawbacks of existing pile-drivers, particularly for offshore pile-driving, lie in the fact that such pile-drivers are very heavy structures. In offshore applications they are operated by large vessels with heavy cranes provided thereon. The piles are driven one by one into the ground.
The pile-driving itself usually takes place by dropping a ram forming part of a pile hammer onto the pile from some height via a striker plate. Typical properties of such a pile hammer for striking a monopile for the purpose of offshore wind turbines are a length of about 15 m and a mass of about 200 tons (with a ram of 100 tons), as well as an associated striker plate of about 200 tons. Piles are becoming increasingly larger in diameter and length, and piles of 1000 tons and having a diameter of 7 m are currently already being driven. The impact of the falling ram drives a pile into the ground but is accompanied by a considerable noise production. This noise production is particularly undesirable in offshore operations, since sound carries very far in water and may thereby disrupt marine life a great distance away from the pile-driving location.
Proposed in the non-prepublished Netherlands patent application NL 2008169 of Applicant is a pile-driver wherein a flexible member enclosing a combustion space of variable volume is arranged above and close to the support member. A drawback of applying a flexible member is that this member can tear during use and is difficult to access for replacement purposes.
An object of the present invention is to provide a pile-driver and method for application thereof, wherein said drawbacks do not occur, or at least do so to lesser extent.
Said objective is achieved with the pile-driver according to the invention, comprising:
The operating principle is based on Newton's first and third laws: “action=reaction”. In other words: when an object A exerts a force on an object B, this force is accompanied by an equal but opposite force of B on A. During expansion the combustion space (object A) exerts a force on the medium located thereabove (reaction mass B). According to Newton's third law, the reaction mass (B) exerts an equal but opposite (so downward) force on the combustion space (A). Because the combustion space is located above and close to the support member, the reaction force exerted by the reaction mass on the combustion space will be transmitted via the support member to the pile. The pile hereby undergoes a downward force via the support member, which is utilized according to the invention for the purpose of driving the pile downward into the ground.
In addition, the medium displaced upward during expansion of the combustion space will drop downward again and collide with the support member, where it once again exerts a downward force on the pile via the support member. This operating principle corresponds to the operation of conventional pile-drivers, wherein a ram is dropped from some height onto the pile.
The use of one or more pressure build-up chambers instead of a flexible member provides another significant advantage. In an embodiment in which a flexible member encloses the combustion space, the maximum volume of the combustion space is limited by the maximum stretch of the flexible member. In the embodiment according to the present invention the combustion space can take on a greater volume, and is moreover also more robust.
Applying pressure build-up chambers which enclose a combustion space with an upper part and further comprise a lower part provided with one or more passage openings which are in fluid connection with the liquid chamber, this is in contrast to the pile-driver described in the non-pre-published Netherlands patent application NL 2008169 of Applicant, renders unnecessary the separation provided by the flexible member of NL 2008169 between the combustion chamber and the water. Because such a separating wall can be dispensed with according to the present invention, a more robust pile-driver is obtained which is moreover not limited by the maximum stretch of any flexible member.
In contrast to the typical steel-on-steel impact sound of conventional pile-driving, the pile-driving process according to the invention is accompanied by another type of sound which is less harmful to marine life.
According to a preferred embodiment, the pressure build-up chamber forms a rigid housing, which is robust.
According to a further preferred embodiment, the one or more pressure build-up chambers are attached inside the liquid chamber to the support member. When the fuel in the pressure build-up chambers is ignited and an expansion takes place in the combustion space enclosed by the pressure build-up chambers, the thereby occurring pressure build-up can result almost directly, through the passage openings provided in the lower part of the pressure build-up chambers, in a pressure build-up above the support member.
According to a further preferred embodiment, the one or more side walls of the liquid chamber separate the liquid from the surrounding area. Because the medium is located in the pile hammer or the pile and is thereby closed off at least by the wall of the pile hammer or the pile from the water present outside the pile-driver, only this medium is displaced as a result of the expansion of the combustion space. Because the displaced medium is isolated from the surrounding area, a shockwave in the surrounding water is prevented. Shockwaves impacting marine life are thus prevented during the pile-driving operations.
According to a further preferred embodiment, the liquid present above the support member in the liquid chamber is water. Water is present in abundance particularly in the case of offshore pile-driving, whereby transport of an alternative medium to the location is unnecessary. A further advantage of water is the high heat transfer coefficient thereof, whereby there is rapid discharge and distribution of the heat released during combustion.
According to a further preferred embodiment, the pile-driver further comprises a fuel supply channel for carrying fuel into the combustion space, and a combustion product discharge channel for discharging combustion products after combustion. Because the combustion space can be filled with fuel and emptied of combustion products in a short time, the system is suitable for a series of successive combustions in a relatively short period of time. It is otherwise noted that, if desired, the same channel can alternately fulfil both functions of fuel supply and combustion product discharge. In that case the channel functions at one moment as the fuel supply channel and the next moment as combustion product discharge channel.
According to a further preferred embodiment, at least a closure is provided which, together with the support member and the one or more side walls, forms a liquid chamber with a volume closed in substantially gas-tight manner, and supply means are further provided for the purpose of thereby carrying a fluid into and/or out of the substantially gas-tight liquid chamber. These supply means can for instance comprise a pump and/or a gas bottle.
According to a further preferred embodiment, the fluid is air and/or water, wherein using the fluid air a pre-pressure can be applied in the substantially gas-tight closed space, and the fluid water provides a reaction mass.
A pile which is driven into the ground encounters a total driving resistance which is the sum of the point resistance and the shaft friction resistance. Depending on parameters such as the soil type, length of the pile and the shape of the pile, both resistances and therefore the total driving resistance vary. Influencing the quantity of water and air present in the substantially gas-tight volume by using the pump makes it possible to optimize the pressure build-up profile in accordance with the driving force desired at that moment. Control means which determine the desired driving force for a specific set of parameters can control the pump accordingly. Tests have shown that, when a pre-pressure is applied, only 5 metres water column can already realize a peak pressure of 10-15 bar. Higher peak pressures can be achieved with a higher water column.
The further the pile has already been driven into the ground, the more rigid it is. The shaft friction resistance in particular also increases as the underground length increases. However, because the pile becomes increasingly more rigid, an increasingly larger amount of reaction mass in the form of water column can also be supported in the pile hammer or in a self-driving pile. The increase in the rigidity of the pile allows a higher centre of gravity of the pile, without the stability being adversely affected.
The point resistance and/or the shaft friction resistance can also be reduced by introducing a liquid during driving of the pile, for instance at the head of the pile or along the wall of the pile. An example of such a liquid is grout, a mixture of cement and water. When this grout later cures, a better attachment of the pile to the soil is also achieved, whereby the load-bearing capacity is ultimately higher than if this pile were to be driven without this liquid.
According to a further preferred embodiment, a plurality of pressure build-up chambers are provided which each comprise an ignition mechanism, and wherein control means are further provided which are configured to ignite the fuel in the pressure build-up chambers in a predetermined sequence and/or at predetermined intervals.
The system can be applied more flexibly by using a plurality of combustion spaces. It is thus possible for instance to coordinate successive combustions with each other in optimal manner. It is possible on the one hand to envisage a subsequent combustion space already being filled with fuel while a combustion space which has just been ignited still has to be emptied of the combustion products present therein. The subsequent combustion can on the other hand take place during the descent of the reaction mass displaced upward in a previous combustion such that the pressure build-up is optimized in accordance with the driving resistance to be overcome at that moment. The ignition controlled by the control means provides the option of generating a desired pressure build-up profile.
According to a further preferred embodiment, control means are provided which are configured to inject extra fuel into a combustion space during the combustion of the fuel and/or to vary the moment of ignition. The pressure build-up profile can hereby be optimized in accordance with the driving force desired at that moment. Control means which determine the desired driving force for a specific set of parameters can control injection of extra fuel accordingly.
According to a further preferred embodiment, at least one opening with a pressure-relief valve is provided in or under the support member. It is noted that ‘under’ refers to the orientation during the pile-driving process, i.e. the opening is arranged in the wall part between the support member and the ground into which the pile is driven. Arranging a hole of determined (optionally variable) size under the support member makes it possible to regulate the outflow speed of the liquid present under the support member. The descent speed of the pile as a result of an impact can hereby also be limited.
According to a further preferred embodiment, the opening is variable and control means are provided with which the size of the opening can be controlled. The descent speed of the pile can hereby be controlled even better.
According to a further preferred embodiment, the combustion space is in gas connection with an underpressure space which is configured to suction combustion products released during combustion out of the combustion space. By means of an underpressure the combustion products released during combustion are suctioned out of the combustion space in a very short time. The combustion products can hereby be removed before the medium displaced in upward direction by the combustion drops hack and collides once again with the support member. Because the falling medium does not drop onto a ‘gas spring’ but actually ‘strikes’ the support member, the downward energy transmitted to the support member by this falling medium can be utilized substantially wholly to drive the pile downward into the ground.
According to a further preferred embodiment, the pile-driver is integrated into the pile which forms with its side wall a side wall of the liquid chamber. Because the pile-driver is integrated into the pile, a plurality of piles can be driven substantially simultaneously, whereby marine life is exposed for a much shorter period of time to noise nuisance resulting from the pile-driving. For locations with a water depth of more than 25 metres it is usual to apply special frames, also referred to as space frames or jackets. These framework constructions transmit the forces via a number of piles to the seabed in order to minimize the mass/stiffness ratio. A drawback of such frameworks is that each pile has to be driven individually or each pile is anchored separately, which, with the conventional pile-drivers, takes a number of working hours proportional to the number of piles. Arranging the pile extendably in a post of the framework construction (or space frame or jacket) as desired enables this framework to be submerged to the seabed, after which the pile can be driven downward from the framework into the seabed. Because a conventional pile-driver is not required when the pile-driver is integrated into a pile, according to the invention the different piles can be driven substantially simultaneously into the ground. In the system according to the invention the number of working hours is not therefore proportional to the number of piles: the driving of three piles takes almost the same amount of time as driving a single pile. This is particularly advantageous for marine life, which is exposed for a much shorter period of time to noise nuisance resulting from the pile-driving.
The system according to the invention is therefore able to pile-drive preassembled constructions, wherein the foundation is, if desired, already attached to the wind turbine. Such a construction can be shipped in and submerged before the construction is driven into place.
A further advantage of a conventional pile-driver being unnecessary is that such a heavy structure with correspondingly suitable vessel is unnecessary. It suffices to place a pile using a crane suitable for the purpose and correspondingly suitable vessel, and to drive the pile only partially into the ground, after which the vessel with the crane can be replaced by a smaller vessel. This is particularly advantageous, since operation of such a large vessel and conventional pile-driver involves considerable cost.
Excessive groundwater pressure may occur after pile-driving. This needs time to even out, after which further driving can take place in order to impart sufficient load-bearing capacity to the pile. Where, with a conventional pile-driving technique, a large vessel has to wait for the excessive groundwater pressure to even out, this is unnecessary in the pile-driving system according to the invention when the pile-driver is integrated into a pile. If desired, a small vessel remains behind in order to generate a number of further combustion cycles via the operating principle of the invention, although it is also possible to envisage this taking place wholly autonomously after some time. It is sufficient that enough fuel and control means are available for this purpose.
The invention further relates to a method for driving a pile downward into the ground, comprising the steps of:
According to a preferred embodiment, the method further comprises the steps of:
According to a further preferred embodiment, the method further comprises the step of injecting extra fuel into the combustion space during combustion of the fuel. The pressure build-up profile can hereby be optimized in accordance with the pile-driving force desired at that moment. If desired, control means which determine the desired driving force for a specific set of parameters control the injection of extra fuel accordingly.
According to a further preferred embodiment, at least a closure is provided which, together with the support member and the one or more side walls, forms a liquid chamber with a volume closed in substantially gas-tight manner, and the method comprises the step of carrying a fluid into and/or out of the substantially gas-tight liquid chamber using a supply means such as a pump or gas bottle. Influencing the quantity of water and air present in the substantially gas-tight volume using the supply means enables the pressure build-up profile to be optimized in accordance with the driving force desired at that moment.
According to a further preferred embodiment, the fluid is air and brings about a pre-pressure.
According to a further preferred embodiment, the fluid is water and provides a reaction mass.
According to a further preferred embodiment, the combustion space is in gas connection with an underpressure space and the method comprises the step, almost immediately after a combustion, of suctioning out of the combustion space the combustion products formed therein by the combustion, so that these combustion products are at least substantially removed from the combustion space before the medium displaced in upward direction by the combustion drops back and collides once again with the support member.
According to a further preferred embodiment of the method, a pile-driver according to the invention is applied.
Preferred embodiments of the present invention are further elucidated in the following description with reference to the drawing, in which:
The offshore wind turbine 36 shown in
The operating principle of fixedly driving the wind turbine construction 36 of
It is noted that the operating principle in
The different stages of the operating principle will now be elucidated in more detail with reference to
A fuel mixture is introduced via a fuel supply channel 30 and an oxygen supply channel 31 into the combustion space enclosed by the upper side of the pressure build-up chamber (
If desired, the fuel supply channel 30 supplies a fuel mixture, in which case the oxygen supply channel may be unnecessary. It is even possible to envisage there being a single channel which alternately fulfils the function of the fuel supply channel 30 and that of a combustion gas discharge channel 32 to be discussed below.
When the fuel mixture 29 present in combustion space 22 is ignited with an ignition mechanism 28 (
It is possible to envisage some of fuel mixture 29 being ignited outside the pressure build-up chamber 14 and displacing in burning state via the fuel supply channel 30 to the pressure build-up chamber 14, and bringing to combustion the fuel mixture 29 already present in combustion space 22.
The water level inside the pressure build-up chamber 14 ideally remains slightly above passage openings 26 during the expansion phase so that only water is displaced from the pressure build-up chamber 14 via the passage openings to the space outside the pressure build-up chamber. This guarantees that pile-driver 1 will quickly be operational again for a subsequent combustion cycle, which will be further elucidated with reference to
Combustion products 33 are formed in combustion space 22 by the combustion process of fuel mixture 29 (
The combustion products can be removed from combustion space 22 before water column 42 displaced in upward direction by the expansion drops back and once again collides with support member 8. The falling water column 42 does not hereby come down onto a ‘gas spring’ but collides with support member 8. The downward force exerted by the falling water column 42 on support member 8 can hereby be utilized almost wholly for the purpose of driving pile 2 downward into the ground.
As a pile 2 is driven deeper into ground 40, pile 2 will obtain more stability and be able to bear more mass. The total pile-driving resistance encountered by pile 2 is the sum of the point resistance and the shaft friction resistance. The shaft friction resistance increases as a greater part of pile 2 is driven into ground 40. Since this situation is also associated with a pile 2 which has already obtained some stability, the height of water column 42 in liquid chamber 5 can be increased.
The transmission of forces in a conventional pile-driver (
Water column 42 is separated from the surrounding area by a separating wall 4. In the embodiment in which pile-driver 1 is integrated into pile 2, the inner wall of pile 2 forms this separating wall 4 (
If the pile-driver is integrated into pile 2, support member 8 preferably rests on protrusions or inner edge 6 which is arranged on inner wall 4 of pile 2 and which provides a local narrowing (stage A). Support member 8 is in this way temporarily removable from pile 2 (stage B), for instance by attaching a chain 46 to eye 34 and hoisting the whole. Pile 2 can then be drilled out using a drill 48, which may be necessary in the exceptional situation that the shaft resistance cannot be overcome with combustions according to the operating principle of the invention. After the soil has been drilled out of pile 2, support member 8 with the one or more pressure build-up chambers 14 can be re-placed (stage C).
It is however noted that the above stated situation will probably be a rare occurrence, since pile-driver 1 according to the invention is also suitable—if necessary—for carrying out stronger combustions. The combustion space 22 enclosed by pressure build-up chamber 14 is for this purpose filled to the point that during expansion not only water but also combustion gases 33 are displaced via passage openings 26 out of the volume enclosed by pressure build-up chamber 14 to the space outside pressure build-up chamber 14 (
A drawback is that combustion gases will get into the water column 42 of pile-driver 1, with the result that owing to the gas the driving mass will acquire some compressibility. The desired incompressibility of the water column is restored by allowing the gas time to rise through the water column. This takes time however, whereby these stronger combustions are preferably utilized only when necessitated by the shaft resistance.
According to an alternative embodiment, the connections for the various supply channels 30, 31, 32 and ignition mechanism 28 are arranged in a unit 58 outside liquid chamber 5 of pile-driver 1. A feed channel 60 extending through wall 4 of pile-driver 1 provides the connection to pressure build-up chamber 14. Because unit 58 and all connections of supply channels 30, 31, 32 and ignition mechanism 28 are arranged outside liquid chamber 5, these components are easily accessible.
It is also possible to envisage the pressure build-up chamber 14 being arranged outside liquid chamber 5 of pile-driver 1 (
In a particularly advantageous embodiment in which pile 2 and pile-driver 1 are integrated, at least one opening (not shown) with a pressure-relief valve is provided in the support member 8 itself or, if desired, under support member 8 in the wall of pile 2. Overpressure occurring under support member 8 during pile-driving can escape through this opening from the space enclosed by support member 8, the inner wall of pile 2 and the ground 40. The opening provides a restrictive passage with which the outflow speed can be regulated. The descent speed of pile 2 as a result of an impact can hereby also be limited, whereby the opening reduces the chance of undesired shock load on the crane.
Provided according to a further preferred embodiment (not shown) on the upper side of pile-driver 1 is a closure which, together with support member 8 and the inner wall 4 of pile-driver 1, encloses a volume closed in substantially gas-tight manner. With a pump air and/or water can be introduced into this closed volume, whereby the pressure build-up profile resulting from the combustion of the fuel mixture in combustion space 22 can be optimized for driving pile 2 downward into ground 40. The height of water column 42 can on the one hand be adjusted, and the desired pre-pressure resulting from the quantity of air present in the closed volume can on the other hand be adjusted so as to optimize the desired pressure build-up.
Although they show preferred embodiments of the invention, the above described embodiments are intended solely to illustrate the present invention and not to limit the scope of the invention in any way. When measures in the claims are followed by reference numerals, such reference numerals serve only to contribute toward understanding of the claims, but are in no way limitative of the scope of protection. It is particularly noted that the skilled person can combine technical measures of the different embodiments. The described rights are defined by the following claims, within the scope of which many modifications can be envisaged.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011166 | Jul 2013 | NL | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/NL2014/050475 | 7/11/2014 | WO | 00 |
