WO2013154428A2

WO2013154428A2 - Method of and system for installing foundation elements in an underwater ground formation

Info

Publication number: WO2013154428A2
Application number: PCT/NL2013/050263
Authority: WO
Inventors: Justin Edward STAM
Original assignee: Ihc Holland Ie B.V.
Priority date: 2012-04-11
Filing date: 2013-04-10
Publication date: 2013-10-17
Also published as: EP2847389A2; JP2015513022A; NL2008625C2; US20150078836A1; CN104271843A; WO2013154428A3; AU2013247474A1

Abstract

The invention relates to a method of and system for installing a foundation element, in particular a (mono) pile (2), in a hard underwater ground formation (3) by means of a driver (4). The method comprises the steps of placing a foundation element (2) on the underwater ground formation (3), placing a screen (7) for reducing noise input from the driver (4), driving the foundation element (2) into the ground formation (3) by means of the driver (4) while the screen (7) is positioned about the foundation element (2), and attenuating noise transfer from the underwater ground formation (3) to the outer wall (9) of the screen (7) during at least part of the driving.

Description

Method of and system for installing foundation elements in an underwater ground formation

The invention relates to a method of installing a foundation element, in particular a (mono) pile, in a hard underwater ground formation by means of a driver, such as an hydraulic driver. The method comprises the steps of placing a foundation element on the underwater ground formation, placing a screen for reducing noise input from the driver into the surrounding water, and driving the foundation element into the ground formation by means of the driver while the screen is positioned about the foundation element. The invention further relates to a system for installing foundation elements.

As explained in European patent publication 1 989 358, offshore ramming work is carried out under water to establish foundations, for example, for drilling, platforms and wind turbines. For wind turbines, large monopiles with a diameter of more than four meters are rammed into the seabed. This ramming results in a substantial underwater noise input, which can have a negative impact on marine fauna. To reduce the noise input underwater, in the method and device according to EP 1 989 358, the material that is to be rammed is surrounded by a fixed flooded sleeve. The sleeve advantageously has a sandwich-like structure. In the example shown in Figure 1 of EP 1 989 358, the sleeve has at least one damping guide element for guiding a pile.

EP 1 640 508 relates to a guide device for piles, the device having a frame fastened on a ship-jack-up rig for encompassing and guiding a post, when ramming the post in a benthic division. A nozzle assembly of a blowing device, which can be lowered from an upper standby position

underneath the frame into an operating position at the benthic division, is attached at the frame. The pile is annularly bordered in a blowing operation. The assembly has pipes with exit openings.

WO 2010/151121 relates to a device for the passive reduction of the sound vibrations in a liquid resulting from a sound source arranged below the liquid level of a body of water, the device comprising an elongate tube which can be arranged over the sound source, the tube comprising an outer wall and inner wall, wherein the tube is designed to

maintain a certain desired pressure in the intermediate space between the inner and outer wall. In this case, the pressure is reduced with respect to the ambient pressure. As a result of the reduced pressure, the sound vibrations will less readily travel to the outside and the noise level in the area around the tube is reduced. "The outer wall and inner wall of the tube can be provided one after the other in the body of water, for example by first anchoring the inner wall into the bottom and then anchoring the outer wall which is arranged around it into the bottom. However, it is also possible to place the tube as a whole, that is to say with the inner and outer wall already assembled to form a single part, on the bottom."

It is an object of the present invention to further improve noise mitigation, in particular when driving

foundations elements in hard subsea ground formations and/or when the noise mitigation screen is made of a material having a high modulus of elasticity, e.g. in excess of 100 GPa.

To this end, the method of the present invention comprises attenuating noise transfer from the (underwater) ground formation to the outer wall of the screen during at least part of the driving, preferably by at least

substantially dynamically uncoupling at least the outer wall of the screen from the ground formation.

It was found that the medium, typically (sea) water, between the foundation element, e.g. a monopile, and the screen is not the only acoustic transfer path and that noise generated by the pile driver is transmitted from the pile to the outer wall of the screen also via the ground formation the screen is resting on or in. This is particularly true when the ground formation comprises hard materials, such as rock, concrete blocks (scour protection) or compacted sand, and/or when the screen is made of a material having a high modulus of elasticity. As noise generated by the pulse-like blows of a pile driver contains a wide spectrum of

frequencies, the outer wall of the screen is typically excited at one or more eigenfrequencies , which dampen out relatively slowly. By attenuating noise transfer via the ground formation, such excitation is avoided or at least reduced and overall acoustic radiation is further mitigated.

Attenuation is achieved passively e.g. by reducing, relative to prior art methods and systems, the stiffness (modulus) of the interface between the ground formation and the lower end of at least the outer wall of the screen, or actively e.g. by establishing the main eigenfrequencies of the screen and providing means for extinguishing these frequencies in the noise generated by the pile driver.

In an embodiment, the lower end of the outer wall of the screen is maintained at a distance from, typically above, the ground formation, e.g. by suspending the outer wall from an inner wall of the screen (if the screen is double walled) , from the pile (if the screen is single walled) or from a surface vessel. The distance is preferably in a range from 5 to 200 centimeters, preferably 10 to 100 centimeters, preferably 15 to 70 centimeters.

In another embodiment, the screen is at least 50%, preferably at least 70% buoyant, or even has a buoyancy of 100% or more (at 100%, the density of screen equals the density of the (sea)water), in which case the screen floats. In this latter configuration, it is preferred that the screen is held in position by one or more weights on the ground formation, such as concrete blocks or a bubble ring resting on the ground formation, and connectors, such as straps or chains, connecting the screen to the blocks or ring .

In yet another embodiment, a noise attenuating material, typically in the shape of a ring having a

circumference that corresponds to that of the screen, is being positioned between the lower end of the outer wall of the screen and the ground formation.

The invention further relates to a system for installing foundation elements, in particular (mono) piles, in a hard underwater ground formation, comprising a driver, a surface vessel, and a screen to be placed about the foundation element to reduce noise input from the driver. The system further comprises means for attenuating noise transfer from the ground formation to the outer wall of the screen during at least part of the driving.

In an embodiment, the surface vessel comprises, in addition to a crane for securing the driver, a crane for suspending the screen and maintaining the screen at a distance from the ground formation during at least part of the driving. Note is this respect that known vessels comprise a single crane for handling the pile and screen and for securing the pile driver during operation.

In another embodiment, the screen is at least 50%, preferably at least 70% buoyant or even has a buoyancy of 100% or more and to that end e.g. comprises one or more chambers and/or is made from a material having a density lower than that of water.

In yet another embodiment, the screen is provided with a support, attached to or separate from the screen, of a noise attenuating material, preferably of a material having a modulus that is lower than the modulus of the material of the outer wall of the screen and lower than the modulus of the underwater ground formation. During driving, the support is positioned between the lower rim of the screen and the ground formation.

For the sake of completeness, attention is drawn to the following prior art.

JP 60-159218 discloses a sound insulator for a pile hammer comprising sound insulating cylinders, which are formed from a resilient material and in the shape of bellows. The sound insulating cylinders are secured around a pile .

DE 1 784 396 discloses a pile driving hammer comprising a telescopic sound absorbing sleeve.

EP 2 395 156 relates to a method of installing foundation elements, in particular (mono) piles, comprising the steps of placing a foundation element on the underwater ground formation and holding the foundation element in place by means of a gripper mounted on a surface vessel.

T.J. Carlson et al., "Hydroacoustic Measurements During Pile Driving at the Hood Canal Bridge, September Through November 2004" discloses a HDPE pipe sleeve that fits over a 24 inch pile and reaches from a point above water to the ground elevation below water. The mentioned sleeve diameter and wall thickness are 34 inch and 1 3/8 inch, respectively.

The invention will now be explained in more detail with reference to the Figures, which show a preferred embodiment of the present method and system.

Within the framework of the present invention, the words "hard ground formation" refer to formations, natural or artificial, which, at least at the interface with the screen comprise material having a modulus of elasticity in excess of 10 MPa . Typical examples include, but are not limited to, rock (modulus usually in a range from 10 to 90 GPa) , densely packed sand (modulus usually 20 to 150 MPa) , and so-called scour protection (modulus usually 10 to 90 GPa), i.e. rocks, concrete blocks or the like dumped at the driving site prior to driving and intended to protect installed foundations element from erosion e.g. by strong currents .

Figure 1 is a cross-section of a first embodiment according to the present invention, wherein the noise mitigation screen is suspended from a surface vessel.

Figures 2 and 3 are a perspective view and a cross- section of a second embodiment according to the present invention, comprising an inflatable cushion.

Figure 4 is a perspective view of a third embodiment comprising a floating screen.

It is noted that the Figures are schematic in nature and that details, which are not necessary for

understanding the present invention, may have been omitted.

Figure 1 shows an embodiment of a system 1 according to the present invention for installing a monopile 2 in an underwater ground formation 3, e.g. a seabed. In this example, the monopile 2 has a circular cross-section and a diameter of five meters and is intended to serve, after installation, as the foundation of a wind turbine.

The system 1 comprises an hydraulic driver 4

(depicted in Figure 2), e.g. an IHC Hydrohammer S-1800, connected to a power pack on board of a surface vessel, such as a ship 5 or jack-up barge, a driver screen 6 for securely mounting the driver on the monopile and an anvil (hidden from view by the driver screen) for transmitting impact energy from the driver 4 to the monopile.

The system further comprises a noise mitigation screen 7, made of e.g. steel, to be placed about the

foundation element to reduce- noise input from the driver into the surrounding water. In this example, the screen comprises an inner wall 8 and an outer wall 9, i.e. is double walled, has a circular cross-section and an inner diameter of six meters. The double wall provides one or more chambers 10 for air or a porous material and renders the screen 50% buoyant.

The upper rim of the screen is provided with a detachable extender, which is used to adjust the effective length of screen to the depth of the water at the location where the foundation element is to be installed. In general, it is preferred that, once in place, the sound-insulating screen extends to above the water level.

The ship 5 comprises a first crane 11 to lift and manipulate the monopile 2 and the screen 7 and a second crane (not shown) to secure the hydraulic driver during driving .

Installation of a monopile is carried out for instance as follows. The cables of the crane are attached to the upper end of a monopile stored on the deck of the ship and the monopile is lifted overboard, manipulated to an upright position, lowered onto the seabed and, if required by the circumstances, allowed to penetrate the scour

protection and possibly the seabed under its own weight. At this stage, the monopile is driven, e.g. by means of a vibratory device, into the seabed to a depth of some meters to further stabilize the monopile.

The driver is positioned on top of the monopile and the screen is lifted over the monopile and the driver.

Alternatively, the screen is placed and the driver is subsequently placed inside the screen and on top of the pile. In this position, the pile is driven to the required depth. Finally, the driver is removed, the screen lifted over the pile and placed back on deck or into the sea, and installation is completed.

In accordance with the present invention, at least during driving, a distance in a range from 20 to 100

centimeters is maintained between the lower rim of the screen and the seabed, thus dynamically uncoupling the two. As a result, substantially no noise or vibrations are transmitted to the screen via the seabed. Although noise leaks through the annular opening resulting from the distance, the energy of this noise is significantly less that that of the noise generated by excitation of the outer wall of the screen by the seabed, i.e. overall acoustic radiation is further mitigated.

In the embodiment shown in Figures 2 and 3, the screen 7 rests on an annular inflated cushion 12, which has a modulus of elasticity that is at least one order of magnitude smaller than the modulus of the seabed and the modulus of the screen. Thus, the cushion effectively attenuates at least the higher frequencies, i.e. serves as a low pass filter.

Figure 4 shows a system comprising a screen 7 having a buoyancy in excess of 100%, e.g. achieved by spacing the inner and outer walls of screen farther apart, and a weight 13 for holding the floating screen upright and spaced from the seabed over a distance in a range from 20 to 100 centimeters. In this example, the weight is provided by a ring for generating a bubble screen inside the double walled screen 7, i.e. the outer diameter of the ring is smaller than the inner diameter of the buoyant screen. The screen is attached to the ring by means of straps 14.

The invention is not restricted to the embodiment described above and can be varied in numerous ways within the scope of the claims. For instance, the outer wall of the screen can be suspended from the inner wall of the screen (resting on the ground formation), e.g. by interconnections between the inner and outer walls. It is preferred that such interconnections are made of or provided with a dampening material .

Claims

1. Method of installing a foundation element, in particular a (mono)pile (2), in a hard underwater ground formation (3) by means of a driver (4), comprising the steps of

placing a foundation element (2) on the underwater ground formation (3),

placing a screen (7) for reducing noise input from the driver ( 4 ) ,

driving the foundation element (2) into the ground formation (3) by means of the driver (4) while the screen (7) is positioned about the foundation element (2),

and characterized by

attenuating noise transfer from the ground formation (3) to the outer wall (9) of the screen (7) during at least part of the driving.

2. Method according to claim 1, comprising at least substantially dynamically uncoupling at least the outer wall (9) of the screen (7) from the ground formation (3).

3. Method according to claim 2, wherein at least the lower end of the outer wall (9) of the screen (7) is maintained at a distance from the ground formation (3).

4. Method according to claim 3, wherein the screen (7) is suspended.

5. Method according to claim 3 or 4, wherein the screen (7) is at least 50% buoyant.

6. Method according to claim 5, wherein the screen (7) floats and is held in position by one or more weights (13) on the ground formation (3) .

7. Method according to any one of the preceding claims, wherein a noise attenuating material (12) is being positioned between the ground formation (3) and the lower end of the outer wall (9) of the screen (7) .

8. Method according to claim 7, wherein the modulus of the material is lower than the modulus of the material of the outer wall (9) of the screen (7) and lower than the modulus of the underwater ground formation (3) .

9. System (1) for installing foundation elements, in particular (mono)piles (2), in a hard underwater ground formation (3), comprising a driver (4), a surface vessel (5), and a screen (7) to be placed about the foundation element (2) to reduce noise input from the driver (4), characterised by means (12; 13, 14) for attenuating noise transfer from the ground formation (3) to the outer wall (9) of the screen (7) during at least part of the driving.

10. System (1) according to claim 9, wherein the surface vessel (5) comprises, in addition to a crane for securing the driver (4) during driving, a crane (11) for maintaining the screen (7) at a distance from the ground formation (3) during at least part of the driving.

11. System (1) according to claim 9 or 10, wherein the screen (7) is at least 50% buoyant.

12. System (1) according to claim 11, wherein the screen (7) comprises at least an inner wall (8) and an outer wall (9).

13. System (1) according to claim 12, wherein the screen (7) has a buoyancy in excess of 100% and the system (1) further comprises a weight (13) for maintaining the floating screen (7) upright.

14. System (1) according to any one of claims 9-13, wherein the screen (7) is provided with a support (12) of a noise attenuating material to be positioned between the lower rim of the screen (7) and the ground formation (3) .

15. System (1) according to claim 14, wherein the modulus of the support (12) is lower than the modulus of the material of the outer wall (9) of the screen (7) and lower than the modulus of the underwater ground formation (3) .