Title: drill assembly for excavating vertical annular cavities in the seafloor

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a drill assembly for excavating into a seafloor an annular cavity having a vertically orientated central core. The invention furthermore relates to a method for Method for excavating into the seafloor an annular cavity having a vertically orientated central core.

At present many offshore wind turbine parks are planned to allow for a significant electricity production. To support the wind turbines, foundation piles, also referred to as monopiles, are driven into the seafloor. After a foundation pile is mounted in the sea floor, the wind turbine, comprising a mast, nacelle and blades, is installed on a top end of it.

For reasons of efficiency the wind turbines have an ever increasing capacity and size. Nowadays 8 MW turbines and 14 MW are being planned. In the future even 20 MW turbines are envisaged. In known designs an 8 MW turbine has a diameter of the hub with blades of 160 metres combined with a height of the hub at about 120 metres above sea level. A proposed 14 MW turbine has a blades diameter of 220 metres combined with the hub at about 160 metres above sea level. These larger wind turbines, require larger foundation piles.

Foundation piles for wind turbines typically are a hollow tubular pile having a centreline, a top end, and an open foot end to be mounted vertically into the soil, i.e. into the seafloor.

Foundation piles envisaged for supporting large size wind turbines may have a diameter in the range of 8 and 12 meters, and lengths between 60 and 120 meters. The wall thickness of the pile may be more than 10 centimetres. For example, the pile may have a mass of more than 1000 tonnes, e.g. more than 2000, or even more than 3000 tonnes.

In practical embodiments, the pile is a steel pile, e.g. composed of ring segments that are welded end to end, with each ring segment being composed of arc segments that are welded to one another to form a ring. Foundation pile typically have a circular horizontal cross-section over their entire length. Foundation piles often include a tapered or conical section, e.g. between a larger diameter lower pile section and a smaller diameter pile top section.

The foundation pile installation process comprises the pile driving process, i.e. the process of driving the pile vertically, into the seafloor. The pile driving force, i.e. the force that drives the pile in the axial direction into the sea floor, can be generated by using an impact hammer, for example drop weight pile driver device or an hydraulic impact hammer. This pile driving process generates a lot of noise which has a negative impact on the environment, in particular on wildlife in the environment. Therefore, costly and elaborate noise mitigation devices, e.g. bubble sheets, are to be deployed during the pile driving process.

The increase in diameter of the of foundation piles possibly requires pile driving forces that cannot be delivered by way of traditional impact hammers. Also, each increase in driving force brings an increase in the noise generated during the pile driving process. This is unwanted.

It is an object of a first aspect of the invention to provide a device and a method for mounting foundation piles for supporting large size wind turbines into the seafloor.

It is a further object of the invention to provide an drill device for excavating annular cavities having a large diameter, i.e. having an outer diameter of more than 7,5 meter, for example having an outer diameter of 9,5 meters or more.

It is a further object of the invention to provide a drill assembly that enables installation of large size foundation piles, i.e. foundation piles having a diameter larger than 10 meters, into the seafloor, more in particular that enables driving large size foundation piles into the sea floor while keeping the impact of the pile installation process on the environment, e.g. excessive noise, limited

It is a further object of the invention to provide a method for excavating into the seafloor an annular cavity having a vertically orientated central core.

It is an object of the invention to provide a method to facilitate installation of foundation piles into the sea floor, in particular to facilitate driving wind turbine foundation piles into the seafloor.

It is a further object of the invention to provide a method for preparing the sea floor prior to driving a foundation pile into the seafloor, the preparing of the seafloor facilitating driving the foundation pile into the seafloor.

It is a further object of the invention to provide a method for mounting large size foundation piles for wind turbines into the sea floor, i.e. four mounting wind turbine foundation piles having a diameter of 10 meters or more into the seafloor.

It is yet a further object of the invention to provide a method for driving large size foundation piles into the sea floor while keeping the impact of the pile installation process on the environment, e.g. excessive noise, limited. The invention therefore provides a drill assembly according to claim 1 , a drill assembly according to claim 31 , and a method according to claim 51.

A drill assembly according to the claimed invention comprises an inner tubular, an outer tubular and a drill device having an annular drill body and an annular drill head, wherein the annular drill head is mounted to the drill body via a bearing, for excavating an annular cavity having a vertically orientated central core in the seafloor.

The prior art does not disclose a drill assembly for excavating annular cavities in the seafloor, the drill assembly comprising two tubulars, an annular drill body and an annular drill head, wherein the drill head can be rotated relative to the drill body about a drilling axis.

According to claim 1 , a drill assembly for excavating into a seafloor an annular cavity having a vertically orientated central core and having a predetermined depth, comprises:

- a drill device for excavating the annular cavity in the seafloor, wherein the drill device comprises:

- an annular drill body, extending along a longitudinal axis between a head end and a tail end, wherein the drill body has a central passage to define the central core of the annular cavity; and

- an annular drill head, mounted to the drill body via a bearing that enables the drill head to rotate relative to the drill body about the drilling axis for excavating the annular cavity;

- an inner tubular for supporting the core of the annular cavity while the annular cavity is excavated; and

- an outer tubular, surrounding the drill device and the inner tubular, for supporting an outer wall of the annular cavity while the cavity is excavated; wherein the inner tubular and the outer tubular each have a central axis that coincides with a drilling axis, and preferably each have a length larger than the predetermined depth of the annular cavity to be excavated e.g. have a length of at least 30 meters, for example have a length of 35 or 45 meters; and wherein the drill device is configured to be removably mounted, preferably clamped, to and in the outer tubular with at least part of the drill head extending out of the outer tubular for excavating an annular cavity wide enough for receiving the outer tubular.

To enable the drill assembly according to the invention to excavate annular cavities having a large diameter, e.g. having an outer diameter of 7,5 meters or more, preferably of 10 meters or more, the drill device is provided with an annular drill body and an annular drill head, wherein the annular drill head is mounted to the drill body via a bearing, to enable rotation of the drill head relative to the drill body, and thus relative to the inner and outer tube, while excavating the annular cavity.

The invention therefore provides a drill assembly configured for excavating annular cavities having a large diameter, i.e. having an outer diameter of more than 7,5 meter, for example having an outer diameter of 9,5 meters or more.

It is submitted that annular cavities obtained with a drilling assembly according to the invention can be used to facilitate driving a foundation pile into the sea floor, in particular to drive a foundation pile having an inner diameter larger than the outer diameter of the annular cavity into the seafloor, preferably by using a method according to the invention.

The invention therefore provides a device, i.e. the drill assembly, that enables mounting foundation piles for supporting large size wind turbines into the seafloor without necessarily the need for larger impact hammers and/or increased noise pollution.

The invention thus provides a drill assembly that enables installation of large size foundation piles, i.e. foundation piles having a diameter larger than 10 meters, into the seafloor, more in particular that enables driving large size foundation piles into the sea floor while keeping the impact of the pile installation process on the environment, e.g. excessive noise, limited.

In an embodiment of a drill assembly according to the invention, the bearing is via linear guides mounted to the drill body, such that the bearing can slide parallel to the drilling axis along the drill body, and the drill device comprises one or more extension devices, e.g. multiple cylinders, mounted between the bearing and the drill body for moving the bearing, and thus the drill head, to enable control of the weight pressing down on the drill head during excavating the annular cavity, i.e. during the excavating process. Thus, in such an embodiment, the drill head can be moved relative to the drill body along the drill axis, more in particular during the excavating process can be moved in a vertical direction relative to the drill body. When, during the excavating process, the drill body is supported by for example a crane, the extension devices allow for controlling the pressure on the drill head, i.e. the weight on bit, and to thus control the excavating process, e.g. the speed at which the annular cavity is excavated in the seafloor.

Preferably, the extension devices are hydraulic cylinders, mounted with the pistons parallel to the drilling axis. Alternatively, for example an electric extension device comprising am electric spindle or a rack and pinion comprising an electric drive.

Furthermore, the extension devices preferably are configured to provide a resilient force, for example are configured to function as a spring element, to allow for movement of the drill head relative to the drill body for example when the drill body is supported by a crane and is lowered by said crane during the excavating process.

In an embodiment, the annular drill head is provided with at least one reamer for cutting through the seafloor, and wherein the at least one reamer is movable between an extended position, for excavating the annular cavity, the annular cavity being wide enough to receive the outer tubular, and a retracted position, to enable retraction of the drill body and drill head through the outer tubular.

Thus, in such an embodiment, cutters are provided on a drill face of the drill head, and on the one or more reamers, to cut an annular cavity that has an outer diameter larger than the outer diameter of the outer tubular and preferably has an inner diameter smaller than the inner diameter of the inner tubular of the drilling assembly.

A drill head according to the claimed invention comprises multiple cutters for cutting through hard sections of the seafloor, in this embodiment, some of these cutters are mounted on the one or more reamers.

In the extended position, the reamers extend in a radially outward direction and below the outer tubular. In the retracted position, the reamers have moved inward, towards the drilling axis, to provide the drill head with a reduced outer diameter, i.e. with a diameter small enough to allow for the drill device to be moved inside the outer tubular, i.e. to be retracted through the outer tubular and to be removed from the cavity.

In an embodiment, the annular drill head is provided with at least one suction nozzle for removing seafloor cuttings from below the drill head, and the drill device is provided with at least one suction conduit, connecting the at least one suction nozzle with a pump. Thus, the cuttings are moved via the drill device, more in particular via the suction conduit provided in the drill device, out of the annular cavity. It is submitted that in many drilling techniques, cuttings are removed with a fluid injected into the borehole via the drill device and removed from the borehole via an annular cavity between the outside of a tubular to be mounted in borehole and the wall of the borehole. This may compromise the integrity of the borehole and may require grouting for providing a stable borehole.

In a further embodiment, the at least one suction conduit comprises at least one head section, fixed to the drill head, a body section, fixed to the drill body, and an annular swivel section, connecting the at least one head section with the body section of the at least one suction conduit. Thus, part of the conduit can rotate with the drill head during the excavating process, while staying continuously connected to the section of the conduit mounted to the drill body. Thus, in such an embodiment, the drill head is provided with multiple suction nozzles, preferably provided at regular intervals along the circumference of the drill head, which is beneficial for removing cuttings from below the drill head along the circumference thereof.

In an embodiment, each suction nozzle is connected to a dedicated suction conduit. In such an embodiment there are as many suction nozzles as there are suction conduits.

In an alternative embodiment, a suction conduit bifurcates, preferably at a swivel section, and connects multiple suction nozzles to a single body section of the suction conduit. For example, the suction conduit may comprises a head section that bifurcates to connect multiple suction conduits to a single body section of the suction conduit.

In an embodiment, the annular drill head is provided with multiple suction nozzles, preferably located at regular intervals along the circumference of the drill head, for removing seafloor cuttings from below the drill head, and the drill device is provided with at least two suction conduits, the suction conduits each connecting multiple suction nozzles with a pump, e.g. wherein each suction nozzle is provided with a pump, or wherein multiple suction nozzles share a pump.

In a further embodiment, each of the suction conduits comprises multiple head sections, each fixed to the drill head, a body section, fixed to the drill body, and an annular swivel section, connecting the at least head sections of the particular suction conduit with the body section of the particular suction conduit, and each head section is at one end connected to a suction nozzle in the drill head and at an opposite end to the swivel section. Thus, the suction conduit bifurcates into multiple head sections via the swivel section of the conduit, and each head section connects a suction nozzle to the swivel section of the particular suction conduit. In a further embodiment, the head sections may bifurcate and thus connect multiple suction nozzles to the swivel section of the particular suction nozzle. In an embodiment, a suction conduit comprises multiple body sections that extend between the swivel section of the suction conduit and one or more pumps.

In a further embodiment, each suction nozzle comprises multiple head sections, for example comprises two head sections, each head section extending between the swivel section of the suction conduit and one or more suction nozzles, and the head sections are each provided with a valve such that each of the head sections can selectively be closed or opened, to enable the use of only a selection of the multiple head sections. Thus, in such an embodiment, the number of active suction nozzles can be changed if needed. Also, a selection of head sections can be auxiliary head sections, which auxiliary head sections are closed when an associated primary head section is open. When the primary head section is blocked, e.g. by cuttings or an accumulation of debris, the primary head section can be closed and the associated auxiliary head section can be opened to provide the suction conduit with cuttings. Thus, the excavating process is not hampered by one or more suction nozzles getting blocked while excavating the annular cavity.

In an embodiment, the outer tubular is on the outside provided with multiple guide devices, e.g. ribs, recesses, tracks, the multiple guide devices extending parallel to a longitudinal axis of the outer tubular for cooperating with guide devices provided on a template mounted on, i.e. anchored in, the seafloor and/or on a pile gripper mounted on a vessel, wherein the guide devices are configured for guiding the tubular in the longitudinal direction while preventing rotation of the tubular about its longitudinal axis. Thus, the template and/or pile gripper can be used to support the drill assembly during the excavating of the annular cavity, more in particular prevent the outer tubular from rotating contrary to the rotation of the drill head.

In addition or as an alternative, the drill assembly may be provided with guide devices in the form of stabilising fins that extend along the inner and or outer tubular and extend in a radial direction to cut in the seafloor and thus secure the inner and/or outer tubular, and thus the drill device, against rotation about the drill axis.

In an embodiment, the drill assembly comprises a template and/or a pile gripper that is, in addition to guide devices or instead of guide devices, provided with clamping devices for engaging the outside of the outer tubular to clamp the outer tubular to prevent rotation of the outer tubular.

Thus, the template and/or the pile gripper are configured to engage the drill assembly, preferably the outer tubular of the drill assembly, to secure it against rotation about the longitudinal axis of the outer tubular. For example clamping devices may be provided on the pile gripper and/or template to engage the outer tubular and thus prevent rotation of the outer tubular relative to the pile gripper and/or template. In such an embodiment, the part of the annular cavity is excavated, for example by the drill head being lowered relative to the drill body, while the outer tubular is held by the template and/or pile gripper. Subsequently, the excavating is halted, the outer tubular is released, and the drill assembly, i.e. the tubulars and the drill body, is lowered. Then, the outer tubular is again engaged by the template and/or pile gripper and a new section of the annular cavity is excavated.

In an embodiment, the drill assembly comprises a template configured to be mounted on, i.e. anchored in, the seafloor, for guiding the outer tubular in a vertical direction, i.e. in a direction along the longitudinal axis of the outer tubular, and for preventing rotation of the outer tubular about its longitudinal axis while the drill device is excavating the annular cavity. Thus, the template can be used to support the drill assembly during the excavating of the annular cavity.

In an embodiment, the drill assembly comprises a pile gripper configured to be mounted to a vessel, for guiding the outer tubular in a vertical direction, i.e. in a direction along the longitudinal axis of the outer tubular, and for preventing rotation of the outer tubular about its longitudinal axis while the drill device is excavating the annular cavity. Thus, the pile gripper can be used to support the drill assembly during the excavating of the annular cavity.

In an embodiment, the inner tubular is on an outside thereof provided with engagement devices, and the outer tubular is on the inside thereof provided with engagement devices that can be coupled with the engagement devices provided on the outside of the inner tubular to transfer torsional forces and thus prevent rotation of the outer tubular relative to the inner tubular, and that can be uncoupled to allow for the inner tubular to be retracted with the drill device out of the annular cavity via the inside of the outer tubular.

In an embodiment, the drill assembly comprises a template and/or a pile gripper that is configured to guide the outer tubular and to guide a foundation pile, the foundation pile having an outer diameter larger that the outer diameter of the outer tubular. Thus, in such an embodiment, the template and/or pile gripper is provided with a passage for guiding the outer tubular of the drill assembly and the foundation pile. The passage can be defined by guide devices for both guiding the outer tubular and the foundation pile, which guide devices can be moved in a radial direction to adjust for the difference in diameter of the outer tubular and the foundation pile. In addition, or as an alternative, there may be provided tubular guide devices for guiding the drill assembly and pile guide devices for guiding the foundation pile, wherein the tubular guide devices and the pile guide devices may be moved between an active position for guiding the tubular or foundation pile respectively, and an inactive position. In such an embodiment, the guide devices for guiding the tubular are in the active position and the guide devices for guiding the pile are in an inactive position while excavating the cavity with the drilling assembly and the guide devices for guiding the tubular are in the inactive position and the guide devices for guiding the pile are in the active position while driving the foundation pile into the seafloor.

In yet another embodiment, the template and/or pile gripper is provided with pile guide devices for guiding the foundation pile and with tubular guide devices for guiding the drilling assembly, and the only the tubular guide devices can be moved, for example in a radial direction, between an active and inactive position. Thus, the tubular guide devices can be moved out of the way when the foundation pile is to be guided by the template and/or pile gripper.

In such an embodiment, the template and /or pile gripper can be used for excavating the annular cavity and for driving the foundation pile into the seafloor. Thus it is not necessary to install new devices for guiding the pile and/or remove or replace devices for guiding the tubular prior to switching to the pile driving process. This may save time.

In yet another embodiment, the template comprises an anchor section, comprising anchors driven into the seafloor, and two top sections that can be mounted on the anchor section. One top section is configured for guiding the drill assembly, while the other top section is configured for guiding a foundation pile. Thus, once the annular cavity has been excavated, the top section for guiding the drill assembly, more in particular for guiding the outer tubular of the drill assembly, is replaced with the other top section for guiding the foundation pile.

In a preferred embodiment, the drill assembly comprises a template that is configured to guide both the drill assembly during the excavating process and the foundation pile during the pile driving process. In such an embodiment, the template can be left in position after excavating the annular cavity and is therefore already correctly positioned when receiving the foundation pile for positioning said pile relative to the annular cavity. When a new template has to be mounted in the sea floor prior to installation of the foundation pile, or when only a pile gripper on a vessel is to be used when installing the foundation pile, the template or pile gripper has to be correctly aligned with the annular cavity, which requires extra time and effort.

In an embodiment, the drill assembly is configured to excavate an annular cavity that has a width that is less than 20% of the outer diameter of the annular cavity, for example, wherein the width of the annular cavity is 2,25 meter and the outer diameter of the annular cavity is at least 12 meter.

In a further embodiment, the drill assembly further comprises a wind turbine foundation pile, and preferably comprises a vessel with a pile gripper, the foundation pile has an inner diameter of at least 8 meter, preferably has an inner diameter of at least 10 meter, preferably is a foundation pile for supporting a large size wind turbine. In a further embodiment, the inner diameter of the wind turbine foundation pile is larger than the outer diameter of the outer tubular, for example is 1 meter larger, preferably is 1 ,5 meter lager.

In an embodiment, the outer diameter of the outer tubular is at least 7,5 meters, for example is 10 meters.

In an embodiment, the inner diameter of the inner tubular is at least 4 meters, for example is 6 meters.

In an embodiment, the drill assembly is provided with coupling devices for coupling with a vessel based crane to enable the drill device to be supported by a crane from vessel while excavating the annular cavity in the sea floor, for example the inner tubular is at a tail end thereof configured to be coupled with and supported by a crane, and wherein the crane preferably is to be used for advancing, i.e. to lower, the drill device during the excavating process.

In another embodiment, a vessel can be provided with a drill assembly support for supporting the drill assembly while excavating the annular cavity. Also in this embodiment, the drill assembly is preferably configured for advancing, i.e. to lower, the drill device during the excavating process.

In yet another embodiment, the drill assembly is supported by a template mounted on the sea floor. In such an embodiment, a support vessel may be present, for example for providing power during the excavating process.

In another embodiment, two or more of the above support options may be combined to support the drill assembly.

In an embodiment of the drill assembly according to the invention, the annular drill head is provided with at least one suction nozzle for removing seafloor cuttings from below the drill head and the drill device is provided with at least one suction conduit that connects the at least one suction nozzle with a pump. In a further embodiment, the at least one suction conduit comprises at least one head section, fixed to the drill head, a body section, fixed to the drill body, and an annular swivel section, connecting the at least one head section with the body section of the at least one suction conduit. In a further embodiment, the swivel section of the suction conduit is an annular conduit, the annular conduit extending about a central axis parallel to the drilling axis, for guiding sea floor cuttings from a side inlet, that is connected to the head section of the suction conduit, to a side outlet, that is connected to the body section of the suction conduit.

Preferably, in such an embodiment, the swivel section, similar to the bearing supporting the annular drill head, forms an interface between the drill body and the annular drill head with a part of the swivel section being mounted to the drill body and part of the swivel section being mounted to the drill head, both parts together forming the conduit.

In a further embodiment, the annular conduit of the swivel section is defined by:

- a head wall, mounted to the drill head, wherein the head wall is provided with the side outlet;

- a body wall, mounted to the drill body, wherein the body wall is provided with the side inlet;

- two annular seals, the annular seals each comprising a flexible sealing wall and an annular guide wall having an annular guide surface, the annular seals extending between the head wall and the body wall on opposite sides of the annular conduit, wherein the annular guide wall is mounted to the drill body or to the drill head with the guide surface facing inward, i.e. towards the annular conduit, and the flexible sealing wall is mounted to the drill head or the drill body respectively, and overlaps with the guide surface, and wherein the flexible sealing walls each lie against the inward facing side of one of the guide walls such that they are each pretensioned in an inward direction.

In such an embodiment, the flexible sealing wall and the annular guide wall are both concentric with the annular conduit. Also, the flexible sealing wall moves along the annular guide surface when the drill head rotates relative to the drill body.

In this embodiment, the annular seals of the swivel section each comprise a part, either the flexible sealing wall or the annular guide wall, that is mounted to the drill body and a part, respectively either the annular guide wall or the flexible sealing wall, that is mounted to the drill head, the parts interacting to form a seal and thus the annular conduit. Thus, the swivel section forms an interface between the drill body and the annular drill head with a part of the swivel section being mounted to the drill body and part of the swivel section being mounted to the drill head, both parts together forming the conduit.

In an embodiment, the annular seals extend in a direction parallel to the drilling axis. In such an embodiment, the flexible sealing wall preferably comprises a flexible and resilient annular seal, that can be moved by the guide wall in a radial direction. The flexible sealing wall can thus compensate for a misalignment of the drill head relative to the drill body, or to compensate for variations of the position of the drill head relative to the drill body during the excavating process, i.e. the drilling of the annular cavity. Thus, the annular seals provide a seal even when the drill body and the drill head are not exactly aligned.

In an embodiment, the flexible sealing walls each comprise a flexible strip, preferably an annular flexible strip, that is plated on opposite sides with flexible metal plates. In this embodiment, the flexible strip and/or the metal plates provide the strip with the pretension that pushes the strip against the annular guide surface. The metal plates contact the annular guide surface and move along the guide surfaces when the drill head rotates relative to the drill body about the drill axis.

The metal plates are at a base end mounted to the drill head or the drill body, and at an opposite free end resiliently lie against the annular guide surface. In an embodiment, the annular guide surface is a wall surface facing the annular conduit, and the wall surface is provided with an annular notch that forms the contact surface for the flexible sealing wall.

In an embodiment, the drill device comprises at least two suction conduits, the suction conduits each comprising at least one head section, which head sections are fixed to the drill head and are each connected to a suction nozzle in the drill head, a body section, fixed to the drill body, and an annular swivel section, connecting the at least one head section with the body section of the respective suction conduit.

In a further embodiment, the swivel sections of the at least two suction conduits each comprise an annular conduit, the annular conduits being concentric and in a radial direction adjacent to each other.

In yet a further embodiment, an annular sub channel is provided between the annular conduits, the sub channel being flanked by the flexible sealing walls of the adjacent swivel sections. Thus, in such an embodiment, the sub channel is separated from the annular conduit of an adjacent swivel section by the flexible sealing wall of that swivel section.

In such an embodiment, during the excavating process when cuttings are removed from below the drill head via the suction conduits, the pressure in the swivel section is lower than the pressure in the sub channel.

It is submitted that the annual seals are positioned against the annular guide surfaces by pretention in the flexible sealing wall.

In an embodiment, the pretension in the flexible sealing walls is such that the flexible sealing walls contact the associated guide surface of the associated guide wall when, during excavating, an underpressure is created in the annular conduits for removing cuttings from below the drill head, while the pressure in the sub channel remains at an ambient level. It is submitted that if the pressure in the annular conduit lowers below a certain level, for example due to a blockage of the head section or the suction conduit upstream of the swivel section, the flexible sealing wall is pulled away from the annular guide surface and water is pulled from behind the flexible sealing wall, preferably from the sub channel provided behind the flexible sealing wall, into the annular conduit. This is beneficial because, the swivel section of the conduit thus guarantees a minimum flow via the suction conduit, even if the suction conduit upstream of the swivel section gets blocked, and thus may prevent damage to the pump, upstream of the swivel section, pumping water through the suction conduit.

In an embodiment, a subchannel is provided behind each of the flexible walls, of a annular conduit of a swivel section, e.g. between the two adjacent annular conduits.

The sub channels preferably provide water at an ambient pressure, i.e. a pressure higher than the suction pressure in the annular conduit during the excavating process, more in particular during excavating activities when cuttings are removed from below the drill head via the one or more suction conduits.

In an embodiment, the flexible sealing walls that flank the sub channel are at a base end thereof mounted to an annular base body, the base body preferably being provided with multiple inlets for providing the sub channel with sea water, preferably at an ambient pressure.

It is submitted that the configuration of the flexible walls, i.e. annular guide surfaces facing the annular conduit, allows for a pressure build up in the annular conduit. When the pressure in the annular conduit is raised, said pressure pushes the flexible sealing walls against the annular guide surfaces, sealing the annular conduit and allowing for a further increase of the pressure. This configuration allows for the pump that pumps water into the suction nozzle and through the conduit, to pump water through the suction conduit and out of the suction nozzle, for example to remove a blockage from the suction nozzle.

In an embodiment, the pump connected to a suction conduit can be switched between a suction mode, wherein the pump pumps water from the suction nozzle into and through the suction conduit for removing cuttings from below the drill head, and a backwash mode, wherein the pump pumps water from the suction conduit towards and out of the suction nozzle, for example to clear the suction nozzle from debris or remove a blockage from the head section of the suction nozzle. In an embodiment, the drill head comprises one or more conduits for guiding water from the annular space between the inner tubular and the outer tubular to below the drill head. Thus, via the annular space between the inner and outer tubular, water can be provided for removing cuttings, the water being pumped away from below the drill head via the suction conduits.

In an embodiment, the inner tubular is fixed to the drill body and the drill body is releasable mounted in the outer tubular, for example by way of clamps mounted on the drill body that engage the inside surface of the outer circumferential tubular. In such an embodiment, the outer circumferential tubular can be released once the circular cavity is drilled and the drill body can be retracted, with the circular drill head and the inner circumferential wall, from the circular cavity while the outer tubular stays in the sea floor as a liner that supports an outer circumferential wall of the circular cavity.

In an embodiment, the drill assembly comprises a template configured to be anchored in the seafloor, for guiding the outer tubular and for preventing rotation of the outer tubular about its longitudinal axis.

In an embodiment, the drill assembly comprises a pile gripper configured to be supported from a vessel, for guiding the outer tubular and for preventing rotation of the outer tubular about its longitudinal axis.

In an embodiment, the inner tubular and outer tubular are coaxial such that they define an annular space between them.

In an embodiment, the inner tubular is fixed to the drill body.

In an embodiment, the drill body is provided with clamping devices that are configured to exert a radially outward clamping force, for clamping the drill device in the outer tubular. In an alternative embodiment, the drill device is fixed to the inner tubular, the inner tubular has a length larger than the length of the outer tubular, and the drill assembly comprises a template mounted on the sea floor and/or a pile gripper or drill assembly support mounted on a vessel, configured to engage the inner tubular and prevent rotation of the inner tubular during the excavating process.

In an embodiment, the drill assembly further comprises a hoisting device for supporting the drill, the inner tubular and the outer tubular during the excavating of the In an embodiment, the annular cavity has an inner diameter of at least 5 meters and preferably has an outer diameter of at least 6 meters.

According to the invention, the pile installation process, for mounting a wind turbine foundation pile into the seafloor, may comprise a seafloor preparing process, comprising excavating an annular cavity in the seafloor. It is submitted that excavating annular holes for wind turbine foundation piles, which typically have a large diameter, i.e. a diameter of 8 meters or more, is not known in the prior art. In a preferred embodiment, the seafloor preparing process comprises excavating an annular cavity having an outer diameter smaller than the inner diameter of the wind turbine foundation pile. In an preferred embodiment, the foundation pile is not mounted in the cavity while it is excavated, i.e. the drill device is separate from the foundation pile, and only after the annular cavity has been excavated is the foundation pile mounted in the seafloor, preferably is not mounted in the annular cavity but is driven into the sea floor.

The invention furthermore provides a drill assembly for excavating into a seafloor annular cavity having a vertically orientated central core and having a predetermined depth, the drill assembly comprises:

- a drill device for excavating the annular cavity in the seafloor, comprising:

- an annular drill body, the drill body having a central passage to define the central core of the annular cavity, and extending along a longitudinal axis between a head end and a tail end;

- an annular drill head for cutting through the seafloor;

- a bearing mounted between the drill body and drill head to enable rotation of the drill head about a drilling axis relative to the drill body;

- at least one drive motor, mounted to the drill body for rotating the drill head; and

- one or more suction conduits, each suction conduit comprising:

- one or more head sections, each mounted to the drill head and each connected to a suction nozzle provided in the drill head for removing seafloor cuttings from below the drill head

- one or more body sections, each mounted to the drill body and each connected to, or connectable to, a pump for pumping water with cuttings through the suction conduit; and

- a swivel section that connects the one or more head sections with the one or more body sections;

- an inner tubular; preferably fixed to the annular drill body, and - an outer tubular surrounding the drill device and the inner tubular, wherein the inner tubular and the drill device are removably mounted to, preferably the drill device is clamped in, the outer tubular with the drill head extending downward out of the outer tubular; wherein the annular drill head is provided with multiple reamers that are each movable between an extended position, for excavating the annular cavity, the annular cavity being wide enough to receive the outer tubular, and a retracted position, to enable retraction of the drill body and drill head through the outer tubular.

The invention furthermore provides a drill assembly for excavating into a seafloor annular cavity having a vertically orientated central core and having a predetermined depth, the drill assembly comprises:

- a drill device for excavating the annular cavity in the seafloor, comprising:

- an annular drill body, the drill body having a central passage to define the central core of the annular cavity, and extending along a longitudinal axis between a head end and a tail end;

- an annular drill head for cutting through the seafloor;

- a bearing mounted between the drill body and drill head to enable rotation of the drill head about a drilling axis relative to the drill body;

- at least one drive motor, mounted to the drill body for rotating the drill head; and

- one or more suction conduits, each suction conduit comprising:

- one or more head sections, each mounted to the drill head and each connected to a suction nozzle provided in the drill head for removing seafloor cuttings from below the drill head;

- one or more body sections, each mounted to the drill body and each connected to, or connectable to, a pump for pumping water with cuttings through the suction conduit; and

- a swivel section that connects the one or more head sections with the one or more body sections;

- an inner tubular; preferably fixed to the annular drill body, and

- an outer tubular surrounding the drill device and the inner tubular, wherein the inner tubular and the drill device are removably mounted to, preferably the drill device is clamped in, the outer tubular with the drill head extending downward out of the outer tubular; wherein the swivel section of each of the suction conduits has an annular conduit, the annular conduit extending about a central axis parallel to the drilling axis, for guiding sea floor cuttings from an inlet that connects to the head section of the suction conduit to an outlet that connects to the body section of the suction conduit, wherein the annular conduit is formed by:

- a head wall, mounted to the drill head, that is provided with the side outlet;

- a body wall, mounted to the drill body, that is provided with the side inlet;

- two annular seals, each comprising a flexible sealing wall and an annular guide wall having an annular guide surface, the annular seals extending between the head wall and the body wall on opposite sides of the annular conduit, wherein the guide wall is mounted to the drill body or to the drill head with the guide surface facing inward, i.e. towards the annular conduit, and the flexible sealing wall is mounted to the drill head or the drill body respectively, and overlaps with the guide surface, and wherein the flexible sealing walls each lie against the inward facing side of one of the guide walls such that they are each pretensioned in an inward direction.

The invention furthermore provides a method for excavating into a seafloor an annular cavity having a vertically orientated central core and having a predetermined depth, using a drill device according to one or more of the preceding claims, wherein the method comprises the step: excavating the vertical annular cavity up to the predetermined depth while supporting the core of the annular cavity with the inner tubular and while supporting a circumferential wall of the annular cavity with the outer tubular.

It is submitted that excavating a cavity in the seafloor prior to mounting a foundation pile in the sea floor, facilitates mounting the foundation pile into the seafloor. The invention thus provides a seafloor preparation process that enables mounting foundation piles for supporting large size wind turbines, i.e. foundation piles having a diameter of 8 meters or more, in the seafloor. The invention furthermore provides a method for excavating into the seafloor an annular cavity having a vertically orientated central core, using a drill assembly according to one or more of the preceding claims, wherein the method comprises the steps:

- excavating the annular cavity while supporting the core of the annular cavity with the inner tubular and while supporting a circumferential wall of the annular cavity with the outer tubular; and

- preferably, retracting the inner tubular and the drill device through the outer tubular, the outer tubular remaining in the annular cavity.

The invention thus provides a method for excavating into the seafloor an annular cavity having a vertically orientated central core. It is submitted that the core of the annular cavity is allowed to collapse when the inner tubular and drill device are retracted from the annular cavity, prior to the foundation pile being mounted in the seafloor. It is submitted that excavating an annular cavity in the seafloor prior to mounting a foundation pile in the sea floor, facilitates mounting the foundation pile into the seafloor, i.e. when the foundation pile is mounted in the seafloor concentric with the annular cavity. Because of the presence of the annular cavity, the soil below and on the inside of the foundation pile is enabled to move away from the foundation pile, towards and into the annular cavity, while the foundation pile is driven into the seafloor. Therefore, less force is required to drive the foundation pile into the seafloor compared to the seafloor not being prepared according to the invention.

Furthermore, by thus preparing the seafloor, the soil on the outside the foundation pile is left undisturbed by the preparation process. Therefore, this soil still has his original compactness, and

To prevent collapse of the outside wall into the annular cavity, once the outer tubular is removed, the annular cavity may be filled, for example with the material removed to excavate the annular cavity. It is submitted that when the annular cavity is filled, the compactness, i.e. density, of this material is substantially less than the material adjacent the annular cavity. Therefore, a filled annular cavity still facilitates driving a foundation pile into the seafloor.

It is submitted that when the annular, after it has been excavated, is filled or partially filled, for example because the core or part of the core has collapsed, or because the annular cavity has been filled with material, for example soil material, for example cutting, it is still referred to as the annular cavity herein.

In an alternative embodiment, only the drill device is retracted from the annular cavity and both the inner tubular and the outer tubular remain in the annular cavity. In this method at least the outer tubular is removed from the annular cavity prior to the foundation pile being mounted in the seafloor. It is submitted that excavating an annular cavity in the seafloor prior to mounting a foundation pile in the sea floor, facilitates mounting the foundation pile into the seafloor, i.e. when the foundation pile is mounted in the seafloor concentric with the annular cavity, less force is required to drive the foundation pile into the seafloor compared to the seafloor not being prepared according to the invention.

In an embodiment, the outer tubular remains in the annular cavity to prevent collapse of the outside wall into the annular cavity while the drill device and optionally the liner tubular, are to be used for drilling another annular cavity. This may for example be useful when there is significant time between the excavating of the annular cavity and the installation of the foundation pile, and support of the outside wall of the annular cavity is required close to the pile driving process. The outer tubular may for example be removed from the circular cavity by a vessel configured to drive the foundation pile into the seafloor, while the vessel that supports the drill assembly has already moved to a new location. Thus, the drill assembly may comprises multiple outer tubulars that are reused.

In an embodiment, the method further comprises:

- after removing the drill device from the annular cavity filling the annular cavity, preferably with cuttings from excavating the annular cavity, preferably up to a height above the sea floor, and

- retracting the outer tubular out of the sea floor and, optionally, retracting the inner tubular from the annular cavity.

The invention thus provides a method preparing the seafloor prior to mounting a foundation pile in the seafloor, the method comprising excavating in the seafloor an annular cavity having a vertically orientated central core and subsequently filling the annular cavity, preferably with cuttings form excavating the annular cavity prior to mounting the foundation pile in the sea floor. In a method, the outer tubular, and optionally the inner tubular, is/are removed from the annular cavity only after the annular cavity is filled and prior to the foundation pile being mounted in the seafloor.

It is submitted that with a pile installation process according to the invention, the pile installation process comprising preparing the seafloor by excavating a preferably annular cavity in the seafloor and mounting a foundation pile concentric with the preferably annular cavity in the seafloor, the foundation pile preferably has an inner diameter that is larger than the outer diameter of the preferably annular cavity, preferably has an inner diameter that is at least 0,60 meter, preferably is at least 1 meter, for example is 1 ,2 meter larger than the outer diameter of the preferably annular cavity. It is submitted that such an installation process facilitates installation of foundation piles into the sea floor, in particular facilitates driving wind turbine foundation piles into the seafloor, and enables driving large size foundation piles, i.e. foundation piles having an inner diameter of 8 meters or more, into the seafloor using a hammering device and/or a vibration device. Thus the pile can be driven into the seafloor using a relatively small hammering device and/or a vibration device.

In a further embodiment, the method comprises collecting the cuttings from excavating the annular cavity.

In a further embodiment, the height of the outer tubular is such that it allows for filling the annular cavity up to a height above the sea floor, e.g. up to a height of 3 meters above the sea floor. In such an embodiment, the length of the outer tubular is such that it extends the filling height, for example 3 meters, above the sea floor when the annular cavity has been excavated up to its predetermined depth.

It is submitted that the core of the annular cavity is allowed to collapse when the inner tubular and drill device are retracted from the annular cavity, prior to the foundation pile being mounted in the seafloor. It is submitted that excavating an annular cavity in the seafloor prior to mounting a foundation pile in the sea floor, facilitates mounting the foundation pile into the seafloor, i.e. when the foundation pile is mounted in the seafloor concentric with the annular cavity, less force is required to drive the foundation pile into the seafloor compared to the seafloor not being prepared according to the invention.

In an embodiment, the method further comprises:

- prior to the excavating process, lowering the outer tubular of the drill device with an open head end onto the sea floor using a ship mounted crane, and preferably engaging the outer tubular with a vessel mounted pile gripper and/or a template mounted on the sea floor; and

- lowering the inner tubular with the drill device mounted in an open head end thereof into the outer tubular.

As an alternative, the invention provides a method comprising the steps:

- prior to the excavating process, lowering the outer tubular, with the inner tubular and the drill device mounted in the outer tubular, with a head end on the sea floor using a ship mounted crane, and preferably engaging the outer tubular with a vessel mounted pile gripper and/or a template mounted on the sea floor. In an embodiment, the method further comprises: excavating the annular cavity by rotating the drill head relative to the drill body.

In an embodiment, the method further comprises: supporting the drill with a vessel mounted crane while excavating the annular cavity.

In an embodiment, the method further comprises: advancing the drill device while excavating the annular cavity by lowering the drill device using the vessel mounted crane.

In an embodiment, the method further comprises:

- anchoring a template in the sea floor;

- positioning the outer tubular in the template prior to excavating the annular cavity.

In an embodiment, the method further comprises: engaging the outer tubular with the template to prevent the outer tubular from rotating about its longitudinal axis.

In an embodiment, the method further comprises:

- holding the outer tubular with a pile gripper mounted on a vessel; and

- preferably engaging the outer tubular with the pile gripper to prevent the outer tubular from rotating about its longitudinal axis.

In an embodiment, the method further comprises: extending one or more reamers mounted on the drill head to excavate a cavity wide enough to receive the outer tubular, and, after excavating the annular cavity, retracting the one or more reamers to enable retracting the drill device through the outer tubular.

In an embodiment, the method further comprises: pumping water through the body section of one or more suction conduits towards and through the head section of that suction conduit to clear a blockage in the head section.

In an embodiment of a method according to the invention, the suction conduit of the drill device comprises a first head section and a second head section, and the method comprises switching from the first to the second head section when the first head section gets blocked.

The invention furthermore provides a method for mounting a hollow foundation pile, preferably a wind turbine foundation pile, having a diameter of at least 8 meters, more preferably having a diameter of at least 10 meters, for example having a diameter of 12 meters, wherein the method comprises the method for excavating into the seafloor an annular cavity having a vertically orientated central core according to the invention, and wherein the method further comprises the step:

- positioning the foundation pile with an open bottom end on the seafloor, concentric with the, preferably filled, annular cavity, and subsequently driving the foundation pile into the sea floor.

In a further embodiment of this method, the foundation pile has an inner diameter that is larger than the outer diameter of the, preferably filled, annular cavity, and thus is larger than the outer diameter of the outer tubular, for example wherein the foundation pile has an inner diameter that is at least 60 cm larger than the outer diameter of the outer tubular, preferably is at least 120 cm larger than the outer diameter of the outer tubular, for example is 150 cm larger than the outer diameter of the outer tubular.

In an embodiment, the method further comprises: using a template that was used for guiding the outer tubular of the drill assembly, and preferably for preventing the outer tubular of the drill assembly to rotate about its central axis, while excavating the annular cavity, for positioning and/or guiding the foundation pile during installation of the foundation pile into the seafloor.

In an embodiment, the method further comprises: driving the foundation pile into the seafloor using a hammering device or a vibration device, optionally using a vibration device in combination with a hammering device.

In an embodiment, the method further comprises: anchoring at least one marker into the seafloor for positioning a foundation pile relative to the annular cavity, wherein the marker preferably is configured for engaging the lower end of the foundation pile to position the foundation pile relative to the annular cavity prior to driving the foundation pile into the sea floor.

The invention furthermore provides a method for preparing the sea floor prior to driving a foundation pile into the seafloor, the preparing of the seafloor facilitating driving the foundation pile into the seafloor. The method comprises: excavating a cavity, preferably an annular cavity having an outer diameter smaller than the inner diameter of the wind turbine foundation pile, the cavity for example having an outer diameter of 7,5 meters and the foundation pile having an inner diameter of 9 meter. The predetermined depth is the depth required for stable installation of the foundation pile, and is more or less equal to the depth the foundation pile is to be driven into the seafloor. Due to circumstances, for example the composition of the seafloor, the predetermined depth may be less or may be more than the depth the foundation pile is to be driven into the seafloor.

For example, the installation depth for a large size wind turbine foundation pile, the foundation pile having a diameter of 12 meters, may be 35 meters. Thus the foundation pile is to be driven 35 meters into the sea floor and the annular cavity is excavated up to a depth of 35 meters.

In an embodiment, the outer tubular has a length larger than the predetermined depth of the annular cavity to allow for the annular cavity to be filled up to a height above the sea floor, e.g. up to a height of 3 meters above the sea floor.

The foundation pile installation process comprises the pile driving process, i.e. the driving the pile into the seafloor, and may for example also comprise positioning the pile in a correct vertical position relative the a pile installation location prior to driving the pile into the seafloor.

In an embodiment, the annular drill is retracted with both the inner tubular and the outer tubular after the annular cavity has been excavated. For example, the soil may have a consistency that prevents the annular cavity from collapsing, or a liner is positioned in the annular cavity after the excavating process. In yet another embodiment, the drill assembly is configured for supporting a liner on the inside and/or outside, i.e. on the inside and/or outside tubular. Thus the liner or liners remain in the annular cavity when the drill assembly, i.e. the drill device and the inner and/or outer tubular, is retracted from the annular cavity.

In an embodiment, the inner and/or the outer tubular is composed out of multiple segments, preferably annular segments. In a further embodiment, one or more of those annular components are added to the tubular during the drilling process to extend the tubular. In such an embodiment, the initial tubular may have a length that is less than the predetermined depth of the annular cavity. When the drilling process has ended, the tubular is composed out of multiple segments, and has a length larger than the predetermined depth of the annular cavity e.g. has a length of at least 30 meters, for example have a length of 35 meters.

The invention furthermore provides a method wherein, after the annular cavity is excavated up to the predetermined depth, the inner tubular, the outer tubular and the drill device are retracted in combination, while via the suction conduits, or additional conduits provided in the drill assembly, soil is and/or cuttings are delivered below the drill head into the annular cavity to fill up the annular cavity while the drill assembly is retracted. In such a method the drill body of the drill device may be fixed to the outer tubular and the inner tubular because there is no need for extracting the drill device separately from the inner and/or outer tubular. It is submitted that such a method may also be used for preparing the seafloor prior to mounting a foundation pile in the seafloor.

For such a method the invention provides a drill assembly for excavating into a seafloor an annular cavity having a vertically orientated central core and having a predetermined depth, wherein the drill assembly comprises:

- a drill device for excavating the annular cavity in the seafloor, wherein the drill device comprises:

- an annular drill body, extending along a longitudinal axis between a head end and a tail end, wherein the drill body has a central passage to define the central core of the annular cavity; and

- an annular drill head, mounted to the drill body via a bearing that enables the drill head to rotate relative to the drill body about a drilling axis for excavating the annular cavity;

- an inner tubular for supporting the central core of the annular cavity while the annular cavity is excavated; and

- an outer tubular, surrounding the drill device and the inner tubular, for supporting an outer wall of the annular cavity while the annular cavity is excavated; wherein the inner tubular and the outer tubular each have a central axis that coincides with the drilling axis, and preferably each have a length larger than the predetermined depth of the annular cavity to be excavated e.g. have a length of at least 30 meters, for example have a length of 45 meters; and wherein the drill device is mounted, preferably fixed, to the inner tubular and the outer tubular with at least part of the drill head extending out of the outer tubular for excavating the annular cavity wide enough for receiving the outer tubular.

It is submitted that a reamer can be any kind of device suitable for enlarging the annular cavity, in particular below the outer tubular, during the excavating process. In an embodiment, the reamer has cutters that can be expanded or contracted by mechanical or hydraulic devices.

According to a second aspect, the invention furthermore provides a method for installation of a foundation pile to facilitate driving a foundation pile into the sea floor. According to the second aspect, a collapse zone is provided in the sea floor prior to installation of the foundation pile. The collapse zone facilitates soil to move from below the foundation pile during the foundation pile installation process, and thus facilitates driving the foundation pile into the seafloor. Furthermore, with a method according to the second aspect, the soil around the foundation pile remains more or less undisturbed, such that an optimal friction between sea floor and the outside of the foundation pile can be obtained, once the pile has been driven into the sea floor.

The second aspect provides a first foundation pile installation method, the installation method comprising preparing the seafloor to facilitate driving the foundation pile, e.g. a foundation pile for supporting a wind turbine, up to an installation depth into the sea floor, wherein the foundation pile has a circumferential wall that forms a vertical foundation pile receiving zone when the foundation pile is installed in the seafloor; the method comprising:

- providing a central collapse zone by excavating, e.g. drilling or digging, a vertical cavity in the sea floor, wherein the central collapse zone is dimensioned for the pile receiving zone to be formed parallel to, and around, the central collapse zone with a soil transfer zone between the central collapse zone and the receiving zone;

- positioning the foundation pile relative to the collapse zone and landing the foundation pile with a bottom end thereof into the seafloor, thereby positioning the foundation pile receiving zone around the central collapse zone and forming the soil transfer zone between the central collapse zone and the receiving zone;

- driving the pile into the seafloor, e.g. by hammering or vibrating the foundation pile at a top end thereof, thus forming the receiving zone parallel to the collapse zone and around the soil transfer zone, and

- by driving the pile into the seafloor, at least partially collapsing the vertical cavity in the central collapse zone by pushing away soil from below the circumferential wall of the foundation pile into the soil transfer zone, and thus pushing soil from the soil transfer zone into the collapse zone, the transfer of soil towards and into the central collapse zone facilitating driving the pile into the seafloor.

In such an embodiment, the soil transfer zone extends around the central collapse zone. Thus, the collapse zone is an annular shaped zone.

In a further embodiment, the method comprises providing a liner along the inside of the vertical cavity of the central collapse zone, preferably while excavating the vertical cavity. In a further embodiment, the liner is configured to collapse into the central collapse zone by driving the foundation pile into the sea floor, the collapse preferably at least partially being caused by pushing soil away from below the circumferential wall of the foundation pile into the soil transfer zone.

In a further embodiment, the method comprises removing the liner prior to driving the foundation pile into the seafloor, and preferably prior to landing the foundation pile with a bottom end thereof into the seafloor.

In a further embodiment, the method comprises preventing collapse of the collapse zone prior to driving the pile into the seafloor by inserting a support body in the vertical cavity, wherein the support body has an outside support surface that is positioned against a wall of the cavity or against a liner provided along the wall of the cavity, and removing the support body prior to driving the foundation pile into the seafloor, and preferably prior to landing the foundation pile with a bottom end thereof into the seafloor.

In a further embodiment, the method comprises providing a liner along the inside of the vertical cavity of the central collapse zone. The liner can be used to prevent collapse of the central collapse zone due to soil moving from the soil transfer zone into the collapse zone prior to the driving the pile into the seafloor. In such an embodiment, the liner preferably is provided against a wall of the cavity, i.e. the wall that defines the outer perimeter of the central collapse zone and that borders the soil transfer zone.

In a further embodiment, the method comprises providing a grid of central collapse zones, for each facilitating a driving a foundation pile into the sea floor and to thus create a grid of foundation piles.

The second aspect furthermore provides a seafloor preparation process, for preparing the seafloor to facilitate driving a foundation pile, e.g. a foundation pile for supporting a wind turbine, up to an installation depth into the sea floor, wherein the foundation pile has a circumferential wall that forms a vertical foundation pile receiving zone when the foundation pile is installed into the seafloor, the method comprising:

- providing an annular collapse zone around a central zone by excavating, e.g. drilling or digging, one or more vertical cavities in the sea floor, wherein the annular collapse zone is dimensioned for the pile receiving zone to be formed parallel to, and around, the central collapse zone with a soil transfer zone between the annular collapse zone and the receiving zone.

Thus, in this method the collapse zone extends around a central zone. The central zone is provided at the center of the annular collapse zone. In contrast, the method disclosed previously provides a central collapse zone. When there is provided a central collapse zone, the center is covered by the collapse zone and there is no central zone.

In a further embodiment, the method comprises the seafloor preparation process according to the second aspect, the installation method further comprising:

- positioning the foundation pile relative to the annular collapse zone and landing the foundation pile with a bottom end thereof into the seafloor, thereby positioning the foundation pile receiving zone around the annular collapse zone and forming the soil transfer zone between the annular collapse zone and the receiving zone; and

- driving the pile into the seafloor, e.g. by hammering or vibrating the foundation pile at a top end thereof, thus forming the receiving zone parallel to the annular collapse zone and around the soil transfer zone, and

- by driving the pile into the seafloor, at least partially collapsing the one or more vertical cavities in the annular collapse zone by pushing away soil from below the circumferential wall of the foundation pile into the soil transfer zone, and thus pushing soil from the soil transfer zone into the collapse zone, the transfer of soil towards and into the annular collapse zone facilitating driving the pile into the seafloor.

In a further embodiment, the method comprises providing a liner along the inside of each of the one or more vertical cavities of the annular collapse zone, preferably while excavating the one or more vertical cavities.

In a further embodiment, the liner/liners is/are configured to collapse into respectively the one or more vertical cavities of the annular collapse zone by driving the foundation pile into the sea floor, the collapse preferably at least partially being caused by pushing soil away from below the circumferential wall of the foundation pile into the soil transfer zone.

In a further embodiment, the method comprises removing the liner/liners prior to driving the foundation pile into the seafloor, and preferably prior to landing the foundation pile with a bottom end thereof into the seafloor. A liner that is to be removed prior to driving the foundation pile into the seafloor can be a rigid structure, for example a steel annular pile that has an outer circumference that matches the outer circumference of the annular cavity. When the liner is configured to collapse, a metal or plastic annular pile can be used that is designed to easily buckle radially inward under the pressure of soil being pushed from the soil transfer zone towards the annular cavity.

In a further embodiment, the method comprises preventing collapse of the one or more cavities of the annular collapse zone prior to driving the pile into the seafloor by inserting a support body into each of the one or more vertical cavities respectively, wherein the support body/bodies has/have an outside support surface that is positioned against a wall of the respective cavity or against a liner provided along the wall of the respective cavity, and removing the support body/bodies prior to driving the foundation pile into the seafloor, and preferably prior to landing the foundation pile with a bottom end thereof into the seafloor.

The support body may differ from a liner in that it fills the entire cavity, thus preventing collapse of the cavity. The body may for example be an annular structure, e.g. with an outside wall and an inside wall and webbing between the inside and outside wall, that fits the annular cavity.

In a further embodiment, the collapse zone comprises an annular cavity, the annual cavity extending around the central zone, and wherein the annular cavity is provided with an inner liner, for preventing collapse of the core zone, and wherein the outer liner is configured to collapse due to the foundation pile being driven into the sea floor, or wherein the outer liner is removed from the annular cavity prior to the foundation pile being driven into the sea floor.

In a further embodiment, the method comprises providing a grid of annular collapse zones, for each facilitating a driving a foundation pile into the sea floor and to thus create a grid of foundation piles.

In a further embodiment, the vertical cavity of the annular collapse zone has a depth similar to, or larger than the installation depth.

In a further embodiment, the method for providing the collapse zone comprises excavating at least one annular vertical hole around the central zone.

In a further embodiment, the width of the annular hole is larger than the width of the circular wall of the foundation pile, and wherein, when the collapse zone comprises an inner and/or an outer liner, the width of the annular hole is larger than the combined width of the circular wall of the foundation pile and the width of the inner and/or outer liner respectively.

In such an embodiment, preferably the width of the annular hole and the width of the circular wall of the foundation pile are measured perpendicular to the inside or outside surface of a wall defining the annular hole or perpendicular to the inside or outside surface of a wall of the foundation pile. Thus, the width extends in a substantially radial direction relative to a center of the annular hole or the foundation pile.

In a further embodiment, the method comprises providing the collapse zone comprises excavating a series of vertical holes distributed around the central zone.

In a further embodiment, at least one of the one or more holes of the annular collapse zone has a depth similar to, or larger than the installation depth.

In a further embodiment, the one or more vertical cavities are filled with a slurry, for example a slurry of bentonite, to prevent full collapse of the one or more vertical cavities prior to the foundation pile being driven into the sea floor.

In a further embodiment, the liner is a corrugated material, wherein the flutes extend in the longitudinal direction of the liner.

In a further embodiment, the collapse zone is located at least within 90%, preferably within 80%, of the radius of the foundation pile, to facilitate landing of the foundation pile such that there is formed a soil transfer zone between the collapse zone and the foundation pile receiving zone, and wherein the soil transfer zone has a width that is wide enough to prevent the collapse zone from influencing the trajectory of the foundation pile while being landed or driven into the sea floor.

Thus, in such an embodiment, the outer diameter of the collapse zone is at most 0,9 times the radius of the foundation pile, or preferably the collapse zone is at most 0,8 times the radius of the foundation pile. It is noted that when the outer diameter of the collapse zone is reduced, and the radius of the foundation pile stays the same, the soil transfer zone is increased.

In an embodiment, the soil transfer zone has a width that is at least twice the width of the circumferential wall of the foundation pile, preferably is at least 10 times the width of the circumferential wall of the foundation pile, more preferably is at least 10 times the width of the circumferential wall of the foundation pile

In a further embodiment, the collapse zone comprises a soil receiving space, and the volume of the soil receiving space is larger than the volume comprised by the foundation pile receiving zone when the foundation pile is driven into the seafloor at installation depth.

In a further embodiment, the sea floor preparation method is performed from a vessel, preferably a floating vessel, and excavating the one or more vertical cavities of the annular/central collapse zone comprises controlling and/or supporting an excavating device for excavating the one or more holes.

In a further embodiment, the seafloor preparation method, i.e. creating the collapse zone in the seafloor, is run from a first vessel and the foundation pile installation process, i.e. driving the foundation pile into the seafloor, is run from a second vessel.

In a further embodiment, there is at least twenty four hours between the sea floor preparation process and driving the foundation pile into the sea floor.

In a further embodiment, the foundation pile has a diameter of more than 5 meter, preferably has a diameter of at least 8 meter, for example has a diameter of 10 meter or more.

In a further embodiment, the foundation pile is driven into the seafloor up to an installation depth of at least 20 meters, preferably at least 30 meters, for example 40 meters.

In a further embodiment, the circumferential wall of the foundation pile has a width of at least 5 cm, preferably has a width of at least 8 cm, for example has a width of 10 cm.

In a further embodiment, the foundation pile is configured for supporting a wind turbine.

In a further embodiment, the one or more vertical cavities have a depth that is at least 60% of the pile driving depth.

In a further embodiment, the collapse zone comprises multiple vertical cavities, and the vertical cavities have different depths, for example one or more vertical cavities have a depth of 60% of the pile driving depth, and one or more vertical cavities have a depth of 90% the pile driving depth. In a further embodiment, the foundation pile receiving zone, the soil transfer zone, the collapse zone, and optionally the central zone, are concentric.

It is submitted that preferably the foundation pile receiving zone is formed by driving the foundation pile into the sea floor, and the radius of the foundation pile receiving zone is therefore similar to the radius of the wall of the foundation pile and the depth of the foundation pile receiving zone is similar to the installation depth. Furthermore, the width of the foundation pile receiving zone is similar to the width of the circumferential wall of the foundation pile.

It is furthermore submitted that preferably the actual border between soil transfer zone and foundation pile receiving zone is determined by placing the foundation pile in the foundation pile receiving zone, the foundation pile receiving zone being located below the circumferential wall of the foundation pile, and the soil transfer zone being located directly inward from the circumferential wall of the foundation pile.

The collapse zone comprises one or more holes, which holes are shaped and/or positioned such that they collapse during the pile driving process. Thus, the collapse zone facilitates soil to move away from below the pile during the pile driving process, and thus facilitates driving the foundation pile in the sea floor.

In an embodiment, the combined volume of the one or more holes in the collapse zone is similar to, preferably is larger than, the volume of the pile receiving zone, i.e. the volume of soil to be replaced by the foundation pile when driven into the seafloor up to the pile installation depth. Thus, the volume of soil to be replaced by the foundation pile can be received in the holes of the collapse zone. It is noted that in an embodiment, some of the soil to be replaced with the wall of the foundation pile will be pushed in a radially outward direction, and will thus not be moved towards the collapse zone.

In an embodiment, the circumferential wall of the foundation pile is shaped to push soil towards the collapse zone. For example, the bottom surface of the circumferential wall can be slanted to push the soil predominantly inwards.

In an embodiment, the collapse zone comprises an annular hole, the annular hole having a cross section similar or identical to the cross section of the circumferential wall of the foundation pile. Because the invention facilitates driving the pile into the sea floor, the pile driving process may comprise pile driving devices, for example for hammering and/or vibrating, that engage the top end of the foundation pile. In such a method, no devices, such as drilling devices, excavating devices, etc, are used at the bottom end of the foundation pile, which allows for a less complicated pile driving process. Thus it is not necessary to remove pile driving devices located at the bottom end of the foundation pile once the foundation pile is installed in the seafloor.

The receiving zone is the part of the sea floor that is to be replaced by the wall of the foundation pile.

The soil transfer zone is provided between the collapse zone and the receiving zone.

Typically, holes created for the collapse zone are narrow holes. The holes have a large depth compared to their width and length. Many types of shapes, i.e. cross sections, are possible, e.g. rectangular shaped holes, or circular shaped holes, annular shaped holes.

The one or more holes are distributed over the collapse zone. In an embodiment, the collapse zone comprises multiple circular holes distributed over an annular area, for example distributed in two rings of holes, wherein the holes are evenly distributed over each circle.

The second aspect of the invention facilitates driving a pile into the seafloor and thus enables an efficient pile driving process. Furthermore, since less force is required for driving the pile into the sea floor, less noise is generated during the pile driving process.

It is submitted that the first and second aspect of the invention can be combined. More in particular, a drill assembly comprising a drill device with an annular drill head according to the first aspect of the inventio can be used to provide an annular collapse zone in the seafloor. Preferably, soil is removed to create the collapse zone. It is submitted that a drill assembly can be used for providing the collapse zone, or suction based devices may be used to excavate the one or more holes that form the collapse zone. In an embodiment, the collapse zone may be filled with replacement material, e.g. soil cuttings removed for creating the collapse zone, after the collapse zone is created. The replacement material has a density that is less than the original soil, and may be compacted and/or pushed out of the collapse zone by soil that is moved form the soil transfer zone into the collapse zone when the pile is driven into the seafloor. It will be appreciated by the skilled person that a technical feature discussed herein as required or as optional with respect to one embodiment of the invention may be equally applicable to one or more other embodiments described herein, with the feature performing its designation function. Such combinations are all envisaged herein unless a combination would result in a technical impossible solution and/or not meet the desired functionality.

The invention is by no devices limited to the exemplary embodiment described herein above, but comprises various modifications hereto, in so far as they fall within the scope of the following claims. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. Any reference signs in the claims should not be construed as limiting the scope.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be discussed with reference to the drawings. In the drawings:

Fig. 1 shows a partial side view of an exemplary embodiment of a drill assembly according to the invention;

Fig. 2 shows a perspective view from below from the drill assembly of fig. 1 ;

Fig. 3 shows a side view in cross section of the drill assembly of Fig. 1 ;

Fig. 4 shows a partial perspective view in close up from below of a cutting face of a drill head of the drill assembly of Fig. 1;

Fig. 5 shows a partial perspective view in close up the drill head of fig. 4;

Fig. 6 shows a side view of a baring and a bearing support of the drill assembly of Fig. 1 in isolation;

Fig. 7 shows a perspective view from above of the bearing and bearing support of the drill assembly of Fig. 1 in isolation;

Fig. 8 shows a side view of a drill head and part of the bearing of the drill assembly of Fig. 1 in isolation;

Fig. 9 shows a perspective view from above of the drill head and part of the bearing of the drill assembly of Fig. 1 in isolation;

Fig. 10 shows a perspective view from above of multiple suction conduits in isolation and of part of the drill head of the drill assembly of Fig. 1 ;

Fig. 11 shows a cross section in close up of an exemplary swivel section of a suction conduit according to the invention;

Fig. 12 shows a perspective view of a component of the swivel section of Fig. 11 ; Figs. 13 - 18 show subsequent steps of a method for mounting a wind turbine foundation pile in the seafloor according to the invention, using a drill assembly according to the invention;

Fig. 19 shows a cross sectional side view of the seafloor, wherein the sea floor is prepared for driving a foundation pile into the sea floor according to the invention;

Fig. 20 shows in a top view a stage in a foundation pile installation method according to the invention; and

Fig. 21 shows in a top view of a seafloor that is prepared for driving a foundation pile into the seafloor with an alternative seafloor preparation process according to the invention.

DETAILED DESCRIPTION

The invention provides a drill assembly configured to excavate annular cavities in the seafloor, the cavities having a large diameter, e.g. having an outer diameter of 7,5 meters or more, preferably of 10 meters or more.

An annular cavities obtained with a drilling assembly according to the invention can be used to facilitate driving a foundation pile into the sea floor.

Figure 1 shows a side view of a drill assembly 1 according to the invention, for excavating into a seafloor an annular cavity having a vertically orientated central core, the annular cavity having a predetermined depth. Figure 2 shows a perspective view form below of that drill assembly.

The drill assembly, according to the claimed invention, comprises an inner tubular 14, an outer tubular 15, not shown in figure 1 and figure 2, and a drill device 5 having an annular drill body 6 and an annular drill head 11. The drill head 11 is mounted to the drill body 6 via a bearing 12 such that the drill head can be rotated relative to the drill body about a drilling axis for excavating the annular cavity.

The inner tubular 14 and outer tubular 15 are coaxial such that they define an annular space between them. In the embodiment shown, the drill body 6 is fixed to the inner tubular 14. Furthermore the drill body 6 is provided with clamping devices 45 that are configured to exert a radially outward clamping force, for clamping the drill device 5 in the outer tubular 15.

The drill body 6 is shown in isolation in figures 8 and 9. The drill body 6 extends along a longitudinal axis 7 between a head end 8 and a tail end 9. Furthermore, the drill body 6 has a central passage 10 to define the central core of the annular cavity to be excavated. The drill head 11 is shown in isolation in figures 6 and 7. The drill head 6 is mounted to the drill body 6 via the bearing 12. The bearing 12 enables rotation of the drill head 11 relative to the drill body 6, and about the drilling axis 13, for excavating the annular cavity.

The drill assembly 1 comprises the inner tubular 14 for supporting the core of the annular cavity while the annular cavity is excavated, and comprises the outer tubular 15, surrounding the drill device 5 and the inner tubular 14, for supporting an outer wall of the annular cavity while the annular cavity is excavated.

The drill device 5 according to the invention is configured to be removably mounted, preferably clamped, to and in the outer tubular 15 with at least part of the drill head 11 extending out of the outer tubular 15 for excavating an annular cavity wide enough for receiving the outer tubular.

The inner tubular 14 and the outer tubular 15 each have a central axis 17 that coincides with the drilling axis 13. Furthermore, the inner tubular 14 and the outer tubular 15 each have a length larger than the predetermined depth of the annular cavity to be excavated e.g. have a length of at least 30 meters, for example have a length of 50 meters. Thus, a top end of the inner tubular and the outer tubular is above the seafloor when the annular cavity has been drilled to its predetermined depth. This allows for the inner tubular and outer tubular to support the core and outer wall of the annular cavity, while the upper end of the inner and/or outer tubular can easily be engaged by a tubular removal device, for example by a vessel mounted crane, to remove them from the annular cavity.

In a further embodiment, the height of the outer tubular is such that it allows for filling the annular cavity up to a height above the sea floor, e.g. up to a height of 3 meters above the sea floor. In such an embodiment, the length of the outer tubular is such that it extends the filling height, for example 3 meters, above the sea floor when the annular cavity has been excavated up to its predetermined depth.

The drill assembly 1 enables installation of large size foundation piles, i.e. foundation piles having a diameter larger than 10 meters, into the seafloor, more in particular enables driving large size foundation piles into the sea floor while keeping the impact of the pile installation process on the environment, e.g. excessive noise, limited.

The invention furthermore provides a method for excavating into a seafloor an annular cavity having a vertically orientated central core and having a predetermined depth, using the drill assembly 1. The method comprises the step: excavating the vertical annular cavity up to the predetermined depth while supporting the core of the annular cavity with the inner tubular and while supporting a circumferential wall of the annular cavity with the outer tubular.

It is submitted that excavating a cavity in the seafloor prior to mounting a foundation pile in the sea floor, facilitates mounting the foundation pile into the seafloor. The invention thus provides a seafloor preparation process that enables mounting foundation piles for supporting large size wind turbines, i.e. foundation piles having a diameter of 8 meters or more, in the seafloor.

In the embodiment shown, the inner diameter of the inner tubular is 8,5 meters and the outer diameter of the outer tubular is 10 meters. The drill assembly 1 shown is thus configured to excavate an annular cavity that has a width that is less than 20% of the outer diameter of the annular cavity. The configuration is suitable for preparing the seafloor to facilitate driving a wind turbine foundation pile for supporting a large size wind turbine, the section of the foundation pile to be driven into the seafloor having a diameter of 11 ,5 meters.

In an alternative embodiment, the inner diameter of the inner tubular is at least 4 meters, for example is 7 meters, and the outer diameter of the outer tubular is at least 7,5 meters, for example is 9 meters.

Figures 13-18 show a method for excavating into the seafloor an annular cavity having a vertically orientated central core, using the drill device 1. In this method, the drill assembly 1 may be supported by a vessel mounted crane.

Figure 13 and figure 14 show the excavating of the vertical annular cavity while supporting the core of the annular cavity with the inner tubular and while supporting a circumferential wall of the annular cavity with the outer tubular. In the embodiment shown, the drill device is supported by a template mounted on the seafloor.

Figure 15 and figure 16 show the annular cavity after the inner tubular and drill are removed, and with the outer tubular, shown in cross section, still present in the annular cavity.

In the method shown, the core of the annular cavity is allowed to collapse when the inner tubular and drill device are retracted from the annular cavity and prior to the foundation pile being mounted in the seafloor. Furthermore, in a the method shown, the cavity is filled prior to the outer tubular being removed from the annular cavity, see figure 16, to prevent the circumferential wall from collapsing. The material that fills the annular cavity has less density, or in other words is less compact, than the material o the seafloor.

Once the outer tubular has been removed, a foundation pile is driven into the seafloor. This is depicted in figure 16. The foundation pile has an inner diameter that is larger than the outer diameter of the annular cavity. Furthermore, the foundation pile is aligned with the annular cavity, i.e. a central axis of the foundation pile is aligned with a central axis of the annular cavity.

In the method shown in figures 13-18 the same template is used for guiding the drill device and for guiding the foundation pile. The template is configured to be adapted for tubulars having a different diameter. In the embodiment shown, the template is therefore provided with arms that are extend for engaging the drill device and that in a retracted form enable the template to guide a foundation pile having a that is larger than the diameter of the drill device, more in particular is larger than the outer diameter of the outer tubular of the drill device.

It is submitted that excavating an annular cavity in the seafloor prior to mounting a foundation pile in the sea floor, facilitates mounting the foundation pile into the seafloor, i.e. when the foundation pile is mounted in the seafloor concentric with the annular cavity. Because of the presence of the annular cavity, the soil below and on the inside of the foundation pile is enabled to move away from the foundation pile, towards and into the annular cavity, while the foundation pile is driven into the seafloor. Therefore, less force is required to drive the foundation pile into the seafloor compared to the seafloor not being prepared according to the invention.

Furthermore, by thus preparing the seafloor, the soil on the outside the foundation pile is left undisturbed by the preparation process. Therefore, this soil still has his original compactness, and has an optimal grip on the outside of the foundation pile. The preparation process thus enables an optimal embedding of the foundation pile sea floor.

To prevent collapse of the outside wall into the annular cavity, once the outer tubular is removed, the annular cavity may be filled, for example with the material removed to excavate the annular cavity. It is submitted that when the annular cavity is filled, the compactness, i.e. density, of this material is substantially less than the material adjacent the annular cavity. Therefore, a filled annular cavity still facilitates driving a foundation pile into the seafloor. In view of the above, it is submitted that the drill assembly 1 thus enables mounting foundation piles for supporting large size wind turbines into the seafloor without necessarily the need for larger impact hammers and/or increased noise pollution. Also, the method enables an optimal embedding of a foundation pile in the seafloor.

In the embodiment of a drill assembly 1 shown in figure 1 , the bearing 12 is via linear guides 18 mounted to the drill body 6, such that the bearing and the drill head 11 can slide parallel to the drilling axis 13 along the drill body 6.

In the embodiment shown, the drill device 5 comprises one or more extension devices 19, in the embodiment shown multiple cylinders, mounted between the bearing 12 and the drill body 6 for moving the bearing 12, and thus the drill head 11 .

Figure 6 and figure 7 show the bearing 12 and a bearing support in the form of the extension devices 19 in isolation, i.e. separate from the drill body 6 the drill head 11 , the inner tubular 14, and the outer tubular 15. It is submitted that in the embodiment shown, the drill body 6 comprises a construction mounted to the inner tubular 14, the construction comprising multiple gangways 28 encircling the inner tubular.

Thus, in the embodiment shown, the drill head 11 can be moved relative to the drill body 6 along the drill axis 13. More in particular, during the excavating process the drill head 11 can be moved in a vertical direction relative to the drill body 6. When, during the excavating process, the drill body 6 is supported by for example a crane, the extension devices 19 allow for controlling the weight pressing down on the drill head, and thus enable control of the pressure on the drill head, also referred to as the weight on bit.

In the embodiment shown, the hydraulic cylinders 19 are mounted with the pistons parallel to the drill axis. Furthermore, in the embodiment shown, the extension devices are configured to allow for movement of the drill head relative to the drill body for example when the drill body is supported by a crane and is lowered by said crane during the excavating process.

Figure 4 shows a cutting face of the drill head 11 of the drill assembly 1. Figure 5 shows a reamer 20 provided on the drill head. The cutting face of the drill head comprises multiple cutters 20 for cutting through the seafloor. In the embodiment shown, the annular drill head 11 is furthermore provided with multiple reamers 21 for cutting through the seafloor, the reamers being provided with cutters as well.

Each reamer is movable between an extended position and a retracted position. With the reamers in the extended position, the drill head shown is configured for excavating the annular cavity such that it is wide enough to receive the outer tubular 15. The reamers extend outward from the drill head, under the outer tubular, to cut an annular cavity that has an outer diameter larger than the outer diameter of the outer tubular. When the drill head is to be retracted via the outer tubular, the reamers are moved in the retracted position.

In the embodiment shown, the drill device is retracted in combination with the inner tubular. Therefore there is no need for reamers on the inside, i.e. the side facing the core of the annular cavity. In an alternative embodiment, the drill assembly is configured for both the inner tubular and the outer tubular to remain in the annular cavity after the excavating process. In such an embodiment, the drill head is retracted via an annular space formed between the inner tubular and the outer tubular. Furthermore, in such an embodiment, the drill head is preferably provided with reamers on the inside, for excavating an annular cavity wide enough to receive the inner tubular, and on the outside, for excavating an annular cavity wide enough to receive the outer tubular, which reamers can be retracted to make the drill device fit the space between the inner tubular and the outer tubular, and to thus enable retracting the annular drill while the inner tubular and the outer tubular remain in the annular cavity.

Preferably, the drill head is configured to excavate an annular cavity having an inner diameter smaller than the inner diameter of the inner tubular, and having an outer diameter larger than the outer diameter of the outer tubular.

In the embodiment shown, the annular drill head 11 is provided with multiple suction nozzles 22 for removing seafloor cuttings from below the drill head 11. The suction nozzles 22 are provided at regular intervals along the circumference of the drill head 11 , which is beneficial for removing cuttings from below the drill head along the circumference thereof.

The drill device 5 is provided with multiple suction conduits 23, each connecting two suction nozzles 22 with a pump 24. Thus, the cuttings are moved via the drill device, more in particular via the suction conduit provided in the drill device, out of the annular cavity. In the embodiment shown, each of the suction conduits 23 comprises two head sections 25, fixed to the drill head 11, a body section 26, fixed to the drill body 6, and an annular swivel section 27, connecting the head sections 25 with the body section 26 of the at least one suction conduit. Thus, each suction conduit 23 bifurcates at the swivel section 27, and connects two suction nozzles 22 to the single body section 26 of the suction conduit. The suction conduits being provided with a swivel section, allows for part of the suction conduit to rotate with the drill head during the excavating process, while staying continuously connected to the section of the conduit mounted to the drill body.

Figure 10 shows the suction conduits 23 in isolation and of part of the drill head 11 of the drill assembly 1.

In the embodiment shown, each head section 25 is provided with a valve 29 such that each of the head sections can selectively be closed or opened. This enables the use of only one of the two head sections of a suction conduit. Which of the two suction nozzles is used can be changed if needed. Also, one of the head sections can be the primary head section and the other can be an auxiliary head section. The auxiliary head section is closed when the associated primary head section is open, i.e. is used. When the primary head section is blocked, e.g. by cuttings or an accumulation of debris, the primary head section can be closed and the associated auxiliary head section can be opened to provide the suction conduit with cuttings. Thus, the excavating process is not hampered by one or more suction nozzles getting blocked while excavating the annular cavity.

In the embodiment shown, the pumps 24 can be switched between a suction mode, wherein the respective pump pumps water from the suction nozzle 22 into and through the suction conduit 23 for removing cuttings from below the drill head 11, and a backwash mode, wherein the pump pumps water from the suction conduit 23 towards and out of the suction nozzle 22, for example to clear the suction nozzle from debris or remove a blockage from the head section of the suction nozzle.

In the embodiment shown, each of the suction conduits 23 comprises two head sections 25, fixed to the drill head 11 , a body section 26, fixed to the drill body 6, and an annular swivel section 27, connecting the head sections 25 with the body section 26 of the at least one suction conduit. Thus, each suction conduit 23 bifurcates at the swivel section 27, and connects two suction nozzles 22 to the single body section 26 of the suction conduit. The suction conduits being provided with a swivel section, allows for part of the suction conduit to rotate with the drill head during the excavating process, while staying continuously connected to the section of the conduit mounted to the drill body.

The swivel section 27 of the suction conduits 23 is an annular conduit, the annular conduit extending about a central axis parallel to the drilling axis 13, for guiding sea floor cuttings from a side inlet that connects to the head section of the suction conduit to a side outlet that connects to the body section of the suction conduit. The swivel section 27 is depicted in the cross section of the drill assembly 1 in figure 3, with the outer tubular indicated in dotted lines, and is shown in isolation with the suction conduits in figure 10.

In the embodiment shown, the swivel section 27, similar to the bearing supporting the annular drill head, forms an interface between the drill body 6 and the annular drill head 11 with a first part of the swivel section, in the embodiment shown upper part 27A, being mounted to the drill body 6 and part of the swivel section, in the embodiment shown lower part 27B, being mounted to the drill head 11. Both parts of the swivel section together form the annular conduits of the swivel section, see figure 10.

A cross sectional view of an exemplary embodiment of a swivel section 27 of a suction conduit according to the invention is shown in figure 11, while figure 12 shows a component of that swivel section 27. The suction conduit comprises three suction conduits, each comprising a body section, a swivel section and six head sections, two per suction conduit, for removing cutting from below a drill head. The figure depicts the swivel section of the suction conduit only.

The swivel section 27 comprises three annular conduits 32, that are mounted between the drill head and the drill body of a drill assembly, similar to the swivel section shown in figure 3 and figure 10. The swivel section is configured to be part of a drill device according to the invention.

In this embodiment, the annular conduits 32 of the swivel section 31 are each defined by:

- a head wall 33, mounted to the drill head of a drill device, wherein the head wall 33 is provided with two side outlets connecting the two head sections to the annular conduit;

- a body wall 34, mounted to the drill body of a drill device, wherein the body wall 34 is provided with a side inlet connecting the annular conduit to a body section of the suction conduit; - two annular seals 35, the annular seals each comprising an flexible sealing wall 36 and an annular guide wall 37 having an annular guide surface 38, the annular seals 36 extending between the head wall 33 and the body wall 34 on opposite sides of each of the conduits.

In the embodiment shown the annular guide wall 37 is mounted to the drill body, with the guide surface facing the annular conduit 32. The flexible sealing wall 36 is mounted to the drill head and overlaps with the annular guide surface 37. Furthermore, the guide walls of adjacent annular conduits are combined into a single guide wall, the isngle guide wall having two annular guide surfaces.

The flexible sealing walls 36 each lie against the inward facing side of one of the guide walls such that they are each pretensioned in an inward direction. In such an embodiment, the annular flexible sealing wall and the annular guide wall are both concentric with the annular conduit. Furthermore, the flexible sealing wall moves along the annular guide surface when the drill head rotates relative to the drill body.

In this embodiment of a swivel section, the annular seals of the swivel section each comprise a part, in the embodiment shown the annular guide wall, that is mounted to the drill body and a part, in the embodiment shown the flexible sealing wall, that is mounted to the drill head, the parts interacting to form a seal and thus the annular conduit. Thus, the swivel section forms an interface between the drill body and the annular drill head with a part of the swivel section being mounted to the drill body and part of the swivel section being mounted to the drill head, both parts together forming the conduit.

In this embodiment, the annular seals extend in a direction parallel to the drilling axis. The flexible sealing wall is a flexible and resilient seal, that can be moved by the guide surface in a radial direction. The flexible sealing wall can thus compensate for a misalignment of the drill head relative to the drill body, or to compensate for variations of the position of the drill head relative to the drill body during the excavating process, i.e. the drilling of the annular cavity. Thus, the annular seals provide a seal even when the drill body and the drill head are not exactly aligned.

Figure 12 shows a component 31 of a annular conduit of the swivel section 35, the component 31 comprising a base body 39 with flexible sealing walls 41 mounted to opposite sides of it. In the embodiment shown, the flexible sealing walls 41 each comprise a rubber annular strip 40, that is plated on opposite sides with flexible metal plates 42.

The metal plates 42 are at a base end mounted to the base body 39, and have an opposite free end that is to be placed against a contact surface of a annular notch provided on the annular guide wall of the swivel section. Furthermore, in the embodiment shown, the flexible sealing walls 41 are bent into, i.e. flexed towards, the annular conduit 32, and when a overpressure is generated in the annular conduit, the flexible sealing walls are pushed against the contacts surfaces of the guide walls. The flexible annular rubber strip and the metal plates provide the flexible sealing walls with the pretension that pushes the sealing walls against the annular guide surfaces. The metal plates contact the annular guide surface and move along the guide surfaces when the drill head rotates relative to the drill body about the drill axis.

Also, in the embodiment shown, an annular sub channel 43 is provided between the annular conduits 32. The sub channels 43 are flanked by the flexible sealing walls 36 of each of the adjacent swivel sections 27. Thus, in such an embodiment, the sub channel 43 is separated from the annular conduit 32 of an adjacent swivel section 27 by the flexible sealing wall 36 of that swivel section 27.

In the embodiment shown, the base body 39 is provided with multiple inlets 44 for providing the sub channel 43 with sea water. The sub channels thus comprise water at an ambient pressure, i.e. a pressure higher than the suction pressure in the annular conduit during the excavating process, during excavating activities when cuttings are removed from below the drill head via the one or more suction conduits. thus, during the excavating process, when cuttings are removed from below the drill head via the suction conduits, the pressure in the annular conduits of the swivel section is lower than the pressure in the sub channels 43. However, the pretension in the flexible sealing walls 41 is such that the flexible sealing walls contact the associated guide surface 38 when, during excavating, an underpressure is created in the annular conduits for removing cuttings from below the drill head, while the pressure in the sub channel remains at an ambient level. It is submitted that if the pressure in the annular conduits lowers below a certain level, for example due to a blockage of the head section or the suction conduit upstream of the swivel section, the flexible sealing wall is pulled away from the annular guide surface and water is pulled from the sub channel provided behind the flexible sealing wall, into the annular conduit. This is beneficial because, the swivel section of the conduit thus guarantees a minimum flow via the suction conduit, even if the suction conduit upstream of the swivel section gets blocked, and thus may prevent damage to the pump, upstream of the swivel section, pumping water through the suction conduit. It is submitted that the configuration of the flexible walls, i.e. annular guide surfaces facing the annular conduit, allows for a pressure build up in the annular conduit. When the pressure in the annular conduit is raised, said pressure pushes the flexible sealing walls against the annular guide surfaces, sealing the annular conduit and allowing for a further increase of the pressure. This configuration allows for the pump that pumps water into the suction nozzle and through the conduit, to pump water through the suction conduit and out of the suction nozzle, for example to remove a blockage from the suction nozzle.

The invention furthermore provides a method for excavating into the seafloor an annular cavity having a vertically orientated central core, using a drill assembly according to the invention, wherein the method comprises the steps:

- excavating the annular cavity while supporting the core of the annular cavity with an inner tubular and while supporting a circumferential wall of the annular cavity with the outer tubular; and

- preferably, retracting the inner tubular and the drill device through the outer tubular, the outer tubular remaining in the annular cavity.

The invention also provides a method that comprises a pile installation process for mounting a wind turbine foundation pile into the seafloor, wherein the mounting of the foundation pile is proceeded by a seafloor preparing process that comprises the excavating into the seafloor of the annular cavity having a vertically orientated central core. This pile installation process furthermore comprises driving a wind turbine foundation pile into the seafloor, for example using an impact hammer device and/or a vibrating device.

The seafloor preparing process comprises excavating the annular cavity with an outer diameter smaller than the inner diameter of the wind turbine foundation pile to be mounted in the seafloor. The foundation pile is not mounted in the cavity while it is excavated, i.e. the drill device is separate from the foundation pile. Only after the annular cavity has been excavated, and preferably has been filled up again, is the foundation pile mounted in the seafloor.

Figures 13 - 18 show subsequent steps of a method for mounting a wind turbine foundation pile in the seafloor according to the invention, using a drill assembly 1 according to the invention.

Figure 13 shows a schematic depiction of a drill assembly 1. The drill assembly 1 comprises an inner tubular 14, an outer tubular 15 and a drill device 5. In the embodiment shown, the inner tubular has a length that is larger than the length of the outer tubular. Therefore, the upper end of the inner tubular 14 extends out of the outer tubular 15 at a top end thereof. According to the invention, the drill device 5 comprises a drill body and a drill head. In the figure the drill head 11 of the drill device 5 is shown extending out of the outer tubular 15. Of the drill assembly 1 shown, the inner tubular 14 is fixed to the drill body and the drill body is releasable mounted in the outer tubular 15 by way of clamps mounted on the drill body that engage the inside surface of the outer tubular 15. Thus, the outer circumferential tubular can be released once the circular cavity is drilled and the drill body can be retracted, with the circular drill head and the inner circumferential wall, from the circular cavity, while the outer tubular stays in the sea floor as a liner that supports an outer circumferential wall of the circular cavity.

The drill assembly 1 enables installation of large size foundation piles, i.e. foundation piles having a diameter larger than 10 meters, into the seafloor, more in particular enables driving large size foundation piles into the sea floor while keeping the impact of the pile installation process on the environment, e.g. excessive noise, limited.

The drill assembly 1 is configured for the drill device to be supported by a crane from vessel while excavating the annular cavity in the sea floor. In the particular embodiment shown, the inner tubular is at a tail end thereof configured to be supported by a crane, and the crane is to be used for advancing, i.e. to lower, the drill device during the excavating process. The crane, and the vessel supporting the crane, are not depicted in the figure. In addition, or as an alternative, a vessel can be provided with a drill assembly support for supporting the drill assembly while excavating the annular cavity. Also in this embodiment, the drill assembly is preferably configured for advancing, i.e. to lower, the drill device during the excavating process.

In the embodiment shown, the drill assembly 1 furthermore comprises a template 46 that is mounted on, i.e. anchored in, the seafloor. The template 46 is configured to guide in a vertical direction both the drill assembly 1 , i.e. the outer tubular 15 of the drill assembly, during the excavating process, and a wind turbine foundation pile 49 during the pile driving process. The template can therefore be left in position after excavating the annular cavity and is thus already correctly positioned when receiving the foundation pile for positioning said pile relative to the annular cavity.

The foundation pile 49, shown in figure 18, has an outer diameter that is larger than the outer diameter of the outer tubular 15 of the drill assembly 1. The template 46, in the figures shown in cross section, has an annular configuration that provides a central passage 48 for passing through the drill assembly and the foundation pile. The size of the passage 48 can be adapted for guiding the outer tubular of the drill assembly and for guiding the foundation pile.

In the embodiment shown, the size of the passage 48 of the template is defined by guide devices 50 in the form of retractable guide arms 51 provided with guide surfaces 52 at the ends thereof. The guide surfaces 52 define the size of the passage. In an extend position the guide arms 51 extend in a radially inward direction and the guide surfaces at the ends of the arms are positioned for guiding the outer tubular of the drill assembly. In a retracted position of the guide arms, the guide surfaces are positioned in a radially outward direction for guiding the foundation pile.

The guide devices 50, more in particular the guide surfaces 52 provided on the guide arms 51 , can be moved in a radial direction to adjust for the difference in diameter of the outer tubular and the foundation pile.

In addition, or as an alternative, there may be provided tubular guide devices for guiding the drill assembly and separate pile guide devices for guiding the foundation pile, wherein the tubular guide devices and the pile guide devices may each be moved between an active position for guiding the tubular or foundation pile respectively, and an inactive position.

In such an embodiment, while the drill device is excavating the cavity, the guide devices for guiding the outer tubular of the drill assembly are in the active position and the guide devices for guiding the foundation pile are in an inactive position. When the template is used to guide a foundation pile, the foundation pile being driven into the seafloor, the guide devices for guiding the tubular are in the inactive position and the guide devices for guiding the pile are in the active position while driving the foundation pile into the seafloor.

In yet another embodiment, the template and/or pile gripper is provided with pile guide devices for guiding the foundation pile and with tubular guide devices for guiding the drilling assembly, and only the tubular guide devices can be moved, for example in a radial direction, between an active and inactive position. Thus, the tubular guide devices can be moved out of the way when the foundation pile is to be guided by the template and/or pile gripper.

In such an embodiment, the template and /or pile gripper can be used for excavating the annular cavity and for driving the foundation pile into the seafloor. Thus it is not necessary to install new devices for guiding the pile and/or remove or replace devices for guiding the tubular prior to switching to the pile driving process. This may save time. In the embodiment shown, the template is furthermore configured for preventing rotation of the outer tubular about its longitudinal axis while the drill device is excavating the annular cavity. Therefore, the template is, in addition to the guide devices, provided with clamping devices, not shown in the figures, for engaging the outside of the outer tubular 15 to clamp the outer tubular to prevent rotation of the outer tubular while excavating the annular cavity.

The clamping devices comprise friction surfaces and are configured to force the friction surfaces to the outside of the outer tubular of the drill assembly to thus secure the outer tubular in position. Thus, the template 46 is configured to engage the outer tubular 15 of the drill assembly 1 , to secure it against rotation about the longitudinal axis of the outer tubular.

In such an embodiment, the part of the annular cavity is excavated, for example by the drill head being lowered relative to the drill body, while the outer tubular is held by the template. Subsequently, the excavating is halted, the outer tubular is released, and the drill assembly, i.e. the tubulars and the drill body, is lowered. Then, the outer tubular is again engaged by the template, and a new section of the annular cavity is excavated.

In an embodiment, the drill assembly further comprises a pile gripper configured to be mounted to a vessel, e.g. to be mounted on the deck of a vessel, for guiding the outer tubular in a vertical direction, i.e. in a direction along the longitudinal axis of the outer tubular, and for supporting the drill assembly during the excavating of the annular cavity. Thus the outer tubular is at two positions supported at the seafloor and at the surface, which provides stability to the drill assembly during while excavating the annular cavity. The pile gripper may be configured to engage the outer and/or inner tubular to prevent rotation of the inner tubular, outer tubular and drill body while excavating the annular cavity.

Figures 13-16 show a pile installation process for preparing the seafloor 2 by excavating an annular cavity 3 in the seafloor 2.

The pile installation process comprises preparing the seafloor 2 by excavating an annular cavity 3 in the seafloor 2 and mounting a foundation pile 49 concentric with the annular cavity in the seafloor. The foundation pile 49 has an inner diameter that is larger than the outer diameter of the annular cavity 3. It is submitted that such an installation process facilitates installation of foundation piles into the sea floor, in particular facilitates driving wind turbine foundation piles into the seafloor, and enables driving large size foundation piles, i.e. foundation piles having an inner diameter of 8 meters or more, into the seafloor using a hammering device and/or a vibration device. Thus the pile can be driven into the seafloor using a relatively small hammering device and/or a vibration device.

This example of the method comprises, prior to the excavating process lowering the outer tubular, with the inner tubular and the drill device mounted in the outer tubular, with a head end on the sea floor using a ship mounted crane. The outer tubular is engaged by a vessel mounted pile gripper to guide the drill assembly while being lowered towards the seafloor. The lower end of the outer tubular is lowered into the template mounted on the sea floor, and is thus engaged by the template such that the template can guide the drill assembly during the excavating process.

As an alternative, the outer tubular is lowered prior to the inner tubular and drill device. In this method, prior to the excavating process, the outer tubular of the drill device is lowered with its open head end onto the sea floor using a ship mounted crane. While the outer tubular is lowered, the outer tubular is engaged by a vessel mounted pile gripper and eventually by the template mounted on the sea floor. Once the outer tubular is thus positioned, the inner tubular with the drill device mounted in an open head end thereof is lowered into the outer tubular.

In the shown method, the drill assembly 1 is supported by a vessel mounted crane while excavating the annular cavity. The drill device is advanced, i.e. lowered, during the excavating of the annular cavity by lowering the drill device using the vessel mounted crane. This crane and vessel are not shown in the figures. The drill assembly 1 is furthermore supported by the template 46 that is mounted, i.e. anchored, in the seafloor 2.

The drill device excavates the annular cavity into the seafloor, in the embodiment shown by rotating the drill head relative to the drill body. The cuttings are transported from below the drill head up to the surface via suction conduits of the drill device, the suction conduits extending between the inner tubular and the outer tubular. The cuttings are collected at the surface in for example a barge. Thus, the cuttings, or part thereof, can be used to fill the annular cavity after the excavating process.

In an alternative embodiment, the cuttings may for example be deposited on the seafloor at some distance from the annular cavity. In such an embodiment, the annular cavity may be filled with an other material.

Figure 14 shows the annular device 5 having excavated the annular cavity 3 up to its predetermined depth. The predetermined depth is the depth required for stable installation of the foundation pile, and is more or less equal to the depth the foundation pile is to be driven into the seafloor. Due to circumstances, for example the composition of the seafloor, the predetermined depth may be less or may be more than the depth the foundation pile is to be driven into the seafloor.

For example, the installation depth for a large size wind turbine foundation pile, the foundation pile having a diameter of 12 meters, may be 35 meters. Thus the foundation pile is to be driven 35 meters into the sea floor and the annular cavity is excavated up to a depth of 35 meters.

Figure 15 shows the annular cavity 3 after removing the drill device 5. The inner tubular 14 is removed as well, while the outer tubular 15 remains in the annular cavity 3 to support the outer circumferential wall 16. The outer tubular 15 is shown in cross section.

In the embodiment shown, the core of the annular cavity is allowed to collapse when the inner tubular and drill device are retracted from the annular cavity.

In figure 15 the annular cavity 3 is filled with cuttings 53 from excavating the annular cavity 3. The annular cavity 3 is filled up to a height above the sea floor 2. This is facilitated by the outer tubular 15 still being mounted in the annular cavity 3 and extending above the seafloor surface.

In figure 16, the outer tubular 15 is retracted from the annular cavity 3 and form the seafloor 2. Furthermore, the template is adapted to enable guiding the wind turbine foundation pile. In the embodiment shown, The guide devices 50, more in particular the guide arms 51 , are retracted in a radial direction to adjust the position of the guide surfaces, and to thus compensate for the increase in diameter of the foundation pile.

Figure 17 shows the subsequent mounting of the wind turbine foundation pile. The foundation pile 49 has an inner diameter that is larger than the outer diameter of the annular cavity, and is mounted concentric with the annular cavity 3 in the seafloor 49. The foundation pile is driven into the seafloor using a hammering device or a vibration device, optionally using a vibration device in combination with a hammering device, that is not shown in the figures. Furthermore, during the pile driving process, the foundation pile preferably is supported by a vessel mounted pile gripper.

It is submitted that preparation of the seafloor facilitates driving the wind turbine foundation pile into the seafloor. Also, preparation of the seafloor enables driving large size foundation piles, i.e. foundation piles having an inner diameter of 8 meters or more, into the seafloor using a hammering device and/or a vibration device. Thus the pile can be driven into the seafloor using a relatively small hammering device and/or a vibration device.

Figure 19 shows a cross sectional side view of the seafloor 2, wherein the sea floor is prepared for driving a foundation pile into the sea floor according to the invention. In this figure an instance is shown where the annular cavity 3 is not completely filled with cuttings 53 from excavating the annular cavity 3. When the outer tubular 15 is removed out of the seafloor the outer portion of the central core is collapsed into the annular cavity 3. The annualr cavity is thus filled with material of which the compactness, i.e. density, is substantially less than the material adjacent the annular cavity. Therefore, an annular cavity 3 filled with collapsed material still facilitates driving a foundation pile into the seafloor.

In figure 19 the level of the material in the collapse zone 60 is lower than the seafloor 2. This is caused by the material, in the form of cuttings, that has been removed to excavate the annular cavity 3.

The invention furthermore provides a seafloor preparation process for preparing the seafloor to facilitate driving a foundation pile, e.g. a foundation pile for supporting a wind turbine, up to an installation depth into the sea floor. In an embodiment, the seafloor preparation process comprises providing a cavity that forms a central collapse zone, or comprises providing one or more cavities that form an annular collapse zone around a central zone. In a preferred embodiment the seafloor preparation process comprises providing a single annular cavity, preferably by using drill assembly according to the inventio, that forms a annular collapse zone. The collapse zone has a diameter that is smaller than the diameter of the foundation pile to be installed, such that the foundation pile can be driven into the ground having the collapse zone at its center, i.e. within the area delimited by its circumferential wall. The presence of a collapse zone, being the central or the annular collapse zone, at the center of the foundation pile facilitates soil to move from below the foundation pile during the foundation pile installation process, and thus facilitates driving the foundation pile into the seafloor. Furthermore, with such a method, the soil around the foundation pile remains more or less undisturbed, such that an optimal friction between sea floor and the outside of the foundation pile can be obtained, once the pile has been driven into the sea floor.

Figure 20 shows in a top view a stage in a foundation pile installation method according to the invention, the opt view shows a seafloor 60, a foundation pile 61 , a soil transfer zone 62 and a central collapse zone 63. The collapse zone 63 is a circular cavity excavated in the sea floor 60. In the embodiment shown, the pile is landed onto the seafloor, but is not yet driven into the seafloor. The soil transfer zone is located between the pile 61 and the central collapse zone 63. Furthermore, in the embodiment shown, a liner 64 is provided that prevents premature collapse of the soil transfer zone into the central collapse zone. The liner is configured to buckle when the pile is driven into the seafloor.

The foundation pile installation method, according to the invention comprises preparing the seafloor 60 to facilitate driving the foundation pile 61 , e.g. a foundation pile for supporting a wind turbine, up to an installation depth into the sea floor. The foundation pile has a circumferential wall that forms a vertical foundation pile receiving zone when the foundation pile is installed in the seafloor.

The method comprises the following steps.

Providing the central collapse zone 63 by excavating, e.g. drilling or digging, a vertical cavity in the sea floor, wherein the central collapse zone is dimensioned for the pile receiving zone to be formed parallel to, and around, the central collapse zone 63 with the soil transfer zone between 62 the central collapse zone and the pile receiving zone.

After providing the central collapse zone, positioning the foundation pile 61 relative to the central collapse zone 63 and landing the foundation pile 61 with a bottom end thereof into the seafloor 60, thereby positioning the foundation pile receiving zone around the central collapse zone and forming the soil transfer zone between the central collapse zone and the pile receiving zone.

Subsequently, driving the foundation pile 61 into the seafloor, e.g. by hammering or vibrating the foundation pile at a top end thereof, thus forming the pile receiving zone parallel to the collapse zone and around the soil transfer zone, and by driving the foundation pile 61 into the seafloor 60, at least partially collapsing the vertical cavity, i.e. the central collapse zone, by pushing away soil from below the circumferential wall of the foundation pile 61 into the soil transfer zone 62, and thus pushing soil from the soil transfer zone 62 into the central cavity, i.e. the collapse zone, the transfer of soil towards and into the central collapse zone facilitating driving the pile into the seafloor.

Figure 21 shows in a top view of a seafloor that is prepared for driving a foundation pile into the seafloor with a seafloor preparation process according to the invention. It is noted that the seafloor preparation process can be part of a foundation pile installation method according to the invention. The top shown in figure 21 view shows a seafloor 160, a foundation pile 161, a soil transfer zone 162 and an annular collapse zone 163. The collapse zone 163 is an annular cavity excavated in the sea floor 160. The annular collapse zone 163 extends around a central zone 65. The central zone is formed by the original, undisturbed, sea floors. In the embodiment shown, the pile is landed onto the seafloor, but is not yet driven into the seafloor. The soil transfer zone is located between the pile 161 and the annular collapse zone 163. Furthermore, in the embodiment shown, a liner 164 is provided that prevents collapse of the central zone into the central collapse zone. In the embodiment shown, the liner remains in place while the foundation pile is driven into the sea floor, and after the foundation pile has been driven into the sea floor. In an alternative method, no liner can be sued, or the liner can be removed prior to the pile being driven into the seafloor.

It is submitted that the foundation pile receiving zone is the part of the sea floor that is to be replaced by the wall of the foundation pile. Thus the pile receiving zone is defined by the foundation pile when driven into the seafloor. In the top views shown in the figures, the foundation pile receiving zone is located below the foundation pile, and thus not visible.

The seafloor preparation process, for preparing the seafloor 160 to facilitate driving the foundation pile 161, e.g. a foundation pile for supporting a wind turbine, up to an installation depth into the sea floor, wherein the foundation 160 pile has a circumferential wall that forms a vertical foundation pile receiving zone when the foundation pile is installed into the seafloor, as shown, comprises the following step:

- providing the annular collapse zone 163 around the central zone 165 by excavating, e.g. drilling or digging, one vertical annular cavity in the sea floor 160, wherein the annular collapse zone 163 is dimensioned for the pile receiving zone to be formed parallel to, and around, the central collapse zone 165 with the soil transfer zone 162 between the annular collapse zone 163 and the foundation pile receiving zone.

It is noted that in an alternative embodiment, the annular collapse zone is a zone extending around the central zone 165, and comprising multiple, for example circular cavities.

It will be appreciated by the skilled person that a technical feature discussed herein as required or as optional with respect to one embodiment of the invention may be equally applicable to one or more other embodiments described herein, with the feature performing its designation function. Such combinations are all envisaged herein unless a combination would result in a technical impossible solution and/or not meet the desired functionality. The invention is by no devices limited to the exemplary embodiment described herein above, but comprises various modifications hereto, in so far as they fall within the scope of the following claims. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. Any reference signs in the claims should not be construed as limiting the scope.

Reference signs

01 drill assembly

02 seafloor

03 annular cavity

04 central core

05 drill device

06 drill body

07 longitudinal axis drill body

08 head end of the drill body

09 tail end of the drill body

10 central passage drill body

11 drill head

12 bearing

13 drilling axis

14 inner tubular

15 outer tubular

16 outer wall

17 central axis of the inner and outer tubular

18 linear guides for bearing and drill head

19 extension devices

20 cutters

21 reamer

22 suction nozzles

23 suction conduits

24 pump suction conduit

25 head section suction conduit

26 body section of suction conduit

27 swivel section of suction conduit

28 gangway mounted to inner tubular

29 valve head section

30

31 component of swivel section

32 annular conduits

33 head wall swivel section

34 body wall swivel section

35 annular seal swivel section

36 flexible sealing wall swivel section

37 annular guide wall swivel section

38 guide surface

39 base body of the component

40 rubber annular strip

41 flexible sealing walls base component

42 flexible metal plates

43 sub channel

44 inlet in base body

45 clamping devices provided on drill body

46 template

47

48 central passage template

49 wind turbine foundation pile

50 guide devices provided on the template

51 retractable guide arms of guide devices

52 guide surfaces on guide arms

53 cuttings 60 sea floor

61 foundation pile

62 soil transfer zone

63 central collapse zone 64 liner central collapse zone

65 central zone