The invention relates to a seabed anchoring system comprising an anchoring element to be stabilized in the soil before fully engaging the anchoring element in the seafloor. The invention also relates to a method for such a system to stabilize and add a hollow pile into the soil.

Background of the invention

Piles are often sunk into the soil under bodies of water. A typical suction pile would be sunk by sealing the upper end of the pile and suctioning the inside of the pile, which suctioning drops the pressure within the pile. The pressure drop (hydrostatic under pressure) causes the pressure of the water surrounding the suction pile to force the pile into the soil. A typical driven pile or drilling casing is driven into engagement in the soil by using a pile hammer deployed from a Mobile Offshore Drilling Unit to drive the drilling casing into the soil.

Usually for anchoring elements the penetration into the seafloor is controlled by using a securing and supporting structure as described in patent publication US6273645.

However for anchoring elements having large dimensions such a structure would be too big and difficult to handle. The proposed prior art solution does not describe a method to ensure a controlled penetration of an anchoring element having large dimensions into the soil without requesting large supporting device.

The solution proposed in the present invention enables to ensure a controlled penetration of an anchoring element that can be used to moor vessels, Tension Leg Platforms (TLP), semisubs, spars and any type of floating structure without requesting large supporting device further referred as floater. The solution proposed can also be used for installation of offshore windmills anchoring foundations.

Summary of the Invention

The object of the present invention is to provide a seabed anchoring system comprising an anchoring element to be stabilized in the soil before fully engaging the anchoring element within the seafloor wherein the anchoring element comprises a top flange adapted to receive a suction head and a contact surface for receiving a driving hammer. The object is achieved by the anchoring system according to claim 1.

The proposed seabed anchoring system can also be used for the installation of foundations of offshore platforms and subsea structures. The seabed anchoring system according to the present invention allows installation of foundation and/or substructure of an offshore seabed supported windmill.

One advantage of the present invention is that the anchoring element of anchoring system also comprises a water injection device located at the engagement with the seafloor location part in order to ease the anchoring element penetration in the soil. A further advantage of the present invention is that the anchoring element is a hollow subsea pile that can have a mooring line attachment lug and an additional water injection device located at the lug level within the pile.

Another advantage of the present invention is that the pile is provided with a removable cover comprising a top flange with a suction head, which cover is tightly closing the hollow subsea pile using inflatable seals.

Another object of the present invention is a method for stabilizing a hollow subsea pile in the lower end of a body of water, in which the pile is lowered onto the lower end, the method comprising the steps of:

a) closing the pile with a removable cover comprising a top flange with a suction head

b) reducing the pressure inside the pile to cause the pile to penetrate the lower end and a column of lower end material to penetrate the interior of the pile until the pile

c) removing the cover

d) installing the follower between the top of the pile in order to create a contact surface for hammering the pile during installation.

According to the present invention the method can also comprise the step of injecting some water towards the soil by using water injection device in order to ease its penetration in the soil.

Brief description of the drawings:

The invention will be further described below in connection with exemplary embodiments with reference to the accompanying drawings, wherein Fig. la shows an anchor pile for mooring a floater placed in the soil Fig. lb shows an anchor pile for mooring a tension leg platform (TLP)

Fig. lc shows an anchor pile as a foundation for an offshore windmill

Fig. 2 shows a view of an anchor handling vessel installing an anchor pile into the soil Fig. 3a shows a hollow anchor pile according the invention penetrating by its own weight the soil when lowered

Fig 3b shows the anchor pile of fig 3a penetrating the soil due to hydrostatic underpressure (suction), activated by a ROV

Fig. 3c shows that the suction head of the hollow anchor pile being removed

Fig. 3d shows an underwater pile hammer being connected to the hollow anchor pile with the help of a ROV

Fig. 3e shows the underwater pile hammer connected to the hollow anchor pile and hammering the pile further into the soil

Fig. 3f shows the hollow anchor pile fully penetrated into the soil.

The engagement with the seafloor location part is at the lower end of the anchoring element, The water injection system used in the present invention (not shown) is similar to the one used to install piles in harder soils such as very dense sand. The use of water injection avoids any risk of pile refusal. The water injection device is in a shape of a ring at the lower end of the hollow pile placed at the interior, radially inward injecting water via nozzles that will spray water coming from the installation vessel via a water supply network, or sucked in from the surrounding seawater via a Remote Operated Vehicle (ROV) that is connected to the hollow pile. The water sprayed liquefies the sand at the lower end of the hollow pile and eases the penetration of the pile into the soil during the suction or hammering process. Such a system allows installing offshore mooring elements and (windmill) foundations having large dimensions e.g. 50 meters height and 10 meters diameter.

Usually the suction to stabilization phase longs until the pile is engaged in a 20 meters depth within the soil.

The offshore anchoring element and method can also be used when the top part of the anchoring pile stays above water level which is for example the case in low water depths; in that case the suction and hammering process is started above water level at the upper end of the anchoring pile while the lower end of the anchoring pile is penetrating the seabed. In very low waters even the upper end of the very long anchoring pile stays above water level after installation of the foundation pile; this is advantageous for example for installing offshore windmills in low depth waters as the top part of the windmill can in that case be connected to the installed anchoring element above water level in a dry environment without the use of ROV's or divers.

Fig. la shows an anchor pile 1 for mooring a floater by means of a mooring line 10. The anchor pile 1 is placed in the soil 100 of the seabed.

Fig. lb shows an anchor pile 1 for mooring a tension leg platform (TLP). The anchor pile 1 is placed in the seabed 100. A mooring connection 20, 21 to the TLP is provided on the upper part of the anchor pile 1.

Fig. lc shows an anchor pile 1 as a foundation for an offshore windmill. On the top of the anchor pile 1 a portion of a foundation 30 is placed, which extends above the seabed or soil 100. The foundation is arranged for carrying an offshore windmill or windturbine (not shown).

Fig. 2 shows a view of an anchor handling vessel 300 installing an anchor pile 1 into the soil 100. By a line 21 the anchor pile is positioned in the water 200 above the seabed level 100. Close to the top of the anchor pile an ROV 40 is shown that assists the penetration of the anchor pile into the seabed soil 100.

Fig. 3a shows a hollow anchor pile 1 that is arranged to penetrate by its own weight the soil when lowered. The top of the anchor pile 1 is attached to a suction head 50. Further the anchor pile may be attached to auxiliary positioning lines (not shown) attached to the installation vessel or auxiliary vessels (not shown).

Fig 3b shows the anchor pile of fig 3 a penetrating (arrow P) the soil due to hydrostatic underpressure (suction), activated by the ROV 40.

Fig. 3c shows that the suction head 50 of the hollow anchor pile 1 is being removed

(arrow R) after placing the pile into the soil 100 underwater 200.

Fig. 3d shows an underwater pile hammer or driving hammer 51 being connected

(arrow C) to the hollow anchor pile 1 with the help of the ROV 40.

Fig. 3e shows the underwater pile hammer 51 connected to the hollow anchor pile 1 and hammering(arrow C) the pile 1 further into the soil 100

Fig. 3f shows the hollow anchor pile 1 fully penetrated into the soil 100 of the seabed.

Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.