WO2024147734A1

WO2024147734A1 - Cutting device for a subsea trench cutter or dredging apparatus

Info

Publication number: WO2024147734A1
Application number: PCT/NL2023/050677
Authority: WO
Inventors: Bruno Tack
Original assignee: Seatools B.V.
Priority date: 2023-01-06
Filing date: 2023-12-21
Publication date: 2024-07-11
Also published as: NL2033916B1

Abstract

Cutting device arranged for cutting into a wetted ground formation, such as a seabed, said device comprising a: - rotatable cutting member comprising at least one cutting element extending in at least a radially outward direction of said rotatable cutting member for engaging the wetted ground formation, wherein said rotatable cutting member is arranged to rotate around an axis of rotation, such that the at least one cutting element is arranged to move along a circumferential cutting path around the axis rotation having a predefined non-zero radius; - wherein the cutting device comprises a jetting unit, comprising at least one jet nozzle, wherein said jetting unit is arranged for providing a flow of fluid to the at least one jet nozzle, wherein said at least one jet nozzle is arranged, as seen in a two-dimensional plane perpendicular to the axis of rotation, within the circumferential cutting path and is configured for generating a fluid jet stream that is directed in a jet stream direction that comprises at least a radial outwardly directed component that is parallel to the radial direction with respect to the axis of rotation of said rotatable cutting member, such that, when in use, the at least one cutting element moves around the at least one jet nozzle and wherein, as seen in the two-dimensional plane perpendicular to the axis of rotation the jet stream direction intersects with the circumferential cutting path.

Description

Cutting device for a subsea trench cutter or dredging apparatus

The present invention relates to a cutting device arranged for cutting into wetted ground formation, such as a seabed, a trenching or dredging apparatus comprising such a cutting device and a method of cutting into a wetted ground formation, such as a seabed, using such a cutting device.

In order to protect subsea cables, these cables are often buried into the seabed. The process of burying these cables typically involves creating a trench in the upper section of the seabed, placing the cable therewithin and covering the cable and/or trench with soil to ensure the cable is buried and protected.

Creating such a trench can be, due to the working conditions at the bottom of the sea, quite challenging. The seabed can comprise of different types of soil, such as sand, clay, rock and/or a combination of these, which are all best cut using different tooling. In particular large boulders that can be found in sandy or clay-type soils lead to issues when trenching.

A commonly used trench cutter is for instance a cutter wheel comprising a plurality of cutting elements that are typically chosen to best cope with the local soil conditions. Such a cutter wheel is essentially a large wheel rotating around an axis of rotation that is substantially parallel to the seabed and perpendicular to the cutting direction. The downside of using such a cutting wheel is primarily that the depth of cut is limited to about 50% - 60% of its diameter, such that a trench of 2 meters depth would require a wheel of at least 4 meters, which is unpractical in terms of size and weight.

A device that is then typically used for cutting these trenches is a chain-cutter device. Such a chain cutter comprises a large chain having the cutting elements mounted thereon that is driven, as an endless drive, along a pair of chain wheels. Although such chain-cutters allow for creating deeper trenches, the cutting process has a very low efficiency, as the driving system including the chain has a friction loss of approximately 45%. As the chain itself is susceptible to damage caused by sudden impacts from colliding into, for instance, the above described large boulders, the operation will typically run the chain at a relatively low constant load, such that the impacts can be absorbed. Additionally, such a chain, which is relatively expensive, will last for only about 2 km - 8 km and takes several hours to replace, making the chain cutter trenching process slow and expensive. It is a goal of the present invention, next to other goals, to provide for a cutting device arranged for cutting into a wetted ground formation, such as a seabed, that allows for efficiently cutting and/or transporting of soil, wherein at least one of the above-mentioned problems is at least partially alleviated.

This goal, amongst other goals, is met by cutting device arranged for cutting into a ground formation, in particular a wetted (surface) ground formation, such as an upper section of a wetted soil, such as a seabed, said device comprising a:

- rotatable cutting member comprising at least one cutting element extending in at least a radially outward direction of said rotatable cutting member for engaging the wetted ground formation, wherein said rotatable cutting member is arranged to rotate around an axis of rotation, such that the at least one cutting element is arranged to move along a circumferential cutting path around the axis rotation having a predefined non-zero radius;

- wherein the cutting device comprises a jetting unit, comprising at least one jet nozzle, preferably a plurality of jet nozzles, wherein said jetting unit is arranged for providing a flow of fluid to the at least one jet nozzle, wherein said at least one jet nozzle is arranged, as seen in a two- dimensional plane perpendicular to the axis of rotation, within the circumferential cutting path and is configured for generating a fluid jet stream that is directed in a jet stream direction that comprises at least a radial outwardly directed component that is parallel to the radial direction with respect to the axis of rotation of said rotatable cutting member, such that, when in use, the at least one cutting element moves around the at least one jet nozzle and wherein, as seen in the two- dimensional plane perpendicular to the axis of rotation the fluid jet stream (and therefore also the jet stream direction) intersects with the circumferential cutting path. Preferably, during operation, soil cut away from the wetted ground formation by the cutting member is blown away from the cutting device by at least the fluid jet streams, and preferably the cutting device is free of suction means.

Such a cutting device, which cuts into the soil as a drum cutter wherein such a drum cutter comprises a cylindrical drum having cutting elements mounted to the exterior of the drum, wherein the cylindrical drum is rotated around its axis of rotation which is oriented, with respect to the seabed in a vertically downward to rearwardly downward direction, such that the direction of the axis comprises at least a component that is substantially perpendicular to the seabed surface. This also enables to cut relatively deep trenches. Drum cutters are, however, typically not suitable for bringing the cut-away soil to the top of the seabed, as they have a low transport capacity. Additionally, soil, especially soil types comprising clay, tend to stick to the drum and thereby clog the drum cutter making regular cleaning essential and cumbersome. The cutting device according to the invention improves the efficiency of the cutting and/or trenching operation as the jet nozzle is arranged for jetting and/or flushing the rotatable cutting member during operation from the inside out. Thereby, a build-up of soil that clogs the rotatable cutting member is prevented, as this can continuously be washed away in at least the radially outward direction, thereby not only keeping the rotatable cutting member in a cleaner state, but also aiding in the transport of cut away soil from the trench using the stream of fluid that is generated by the jet nozzle.

Preferably, the jet stream direction of the at least one jet nozzle is directed substantially entirely radially outward, substantially parallel to the radial direction with respect to the axis of rotation of said rotatable cutting member. Preferably, the at least one jet nozzle is arranged radially outwardly, substantially perpendicular to the axis of rotation of the rotatable cutting member.

The jetting unit may comprise a fluid flow driving device, such as a pump, for providing said flow of fluid to the at least one jet nozzle, but may also merely comprise means for guiding said flow of fluid to the at least one jet nozzle, whereby the jetting unit may be arranged for receiving said flow of fluid from an (external) fluid flow driving device. Said jetting unit is preferably arranged for supplying and/or guiding fluid flow, in particular a liquid such as water, e.g. sea water, that is drawn in from the underwater environment surrounding the cutting device. The jetting unit, and the at least one nozzle is preferably arranged to operate with a pressurized fluid having a pressure in the range of 1 - 40 bars, more preferably in the range of 3 - 30 bars, for generating the fluid jet stream.

In a preferred embodiment, the rotatable cutting member comprises a frame member comprising at least one arm member, wherein said arm member extends at a radial distance from the axis of rotation in at least an axial direction and holds said at least one cutting element; wherein, when rotating, said frame member delimits an internal space of said rotatable cutting member and wherein the at least one jet nozzle is arranged within said internal space. Such a construction allows to arrange the jet nozzle within the rotatable cutting member, such that it can efficiently flush out the cut away soil. Additionally, the arm will effectively act as a scoop allowing to transport cut away soil from the cutting zone (i.e. on the side of the cutting device that is in the direction of the cutting direction and faces the uncut section of soil) thereby increasing the transport capacity of cut away soil of the cutting device.

It is then preferred that the frame member comprises a plurality of arm members, wherein each arm member extends at a radial distance from the axis of rotation in at least an axial direction and holds at least one cutting element; wherein, when the frame member comprises three arms or more, the frame member is substantially cage-like shaped; wherein the arm members are preferably evenly spaced apart, as seen along the azimuth direction with respect to the axis of rotation.

By arranging multiple arms and multiple cutting elements, multiple open spaces in between the multiple arms (that act as multiple scoops, as is described above) allow for an increased transport capacity from the cutting zone. The cutting and transporting capacity of the cutting device is increased, leading to an improved efficiency, while still allowing the jet nozzle to efficiently flush out the cut away soil and wash of soil that sticks to the rotatable cutting member, in particular to the arms of the frame member and/or the cutting elements. For instance, boulders can be effectively moved out of the way as the arms will force these to the back of the rotatable cutting member.

Preferably, said frame member defines (at least when rotating) a circumferential surface delimiting an external volume and wherein said external volume is shaped as, or to comprise, a substantially uniform cylinder, a substantially non-uniform cylinder, such as a cone or frusto-cone, a hemi-dome like shape, or a combination of these. This enables the cutter to function as a drum cutter, without the use of a closed off cylinder, as used in drum cutters according to the prior art, that have a low transport capacity and are susceptible to cut away soil clogging the drum cutting member.

In a preferred embodiment, the length of the rotatable cutting member, as measured along the axis of rotation, is larger than the largest radius of a circumferential cutting path of a cutting element, preferably larger than 2 times the largest radius of a circumferential cutting path of a cutting element, more preferably larger than 3 times the largest radius of a circumferential cutting path of a cutting element, most preferably larger than 5 times the largest radius of a circumferential cutting path of a cutting element. This enables to efficiently cut deeper trenches having a depth that exceeds the width of the trench.

The at least one jet nozzle is (at least when used for cutting in the ground formation) preferable directed in a backwardly-oriented direction having a component, preferably the largest component of all respective components of the backwardly-oriented direction, that is directed in the direction opposite to the cutting direction. During cutting, cut away soil is moved by the rotatable cutting member from the cutting zone (i.e. the sides of the rotatable cutting member that face the uncut soil of the respective upper layer, in particular the uncut soil in the cutting/trenching direction) towards a discharging zone, wherein the at least one jet nozzle flushes, sprays and/or jets the cut away soil from the rotatable cutting member. Thereby, the cut away soil is efficiently removed from the cutting zone of the wetted ground formation (e.g., a trench being formed) and the build-up of soil that clogs the rotatable cutting member is prevented, as is described above.

It is preferred that said jetting unit comprise a plurality of jet nozzles that are arranged, as seen in the two-dimensional plane perpendicular to the axis of rotation, within the circumferential cutting path and are configured for generating fluid jet streams that are directed in respective jet stream directions that comprises at least the radial outwardly directed component that is parallel to the radial direction with respect to the axis of rotation of said rotatable cutting member. Multiple jet nozzles can, for instance, enable to clean the rotatable cutting member over a section that extends at least a part, preferably the largest part, of the length of the rotatable cutting member.

It is then preferred that at least a first jet nozzle of the plurality of jet nozzles is configured for generating a fluid jet stream that is directed in a first jet stream direction and at least a second jet nozzle of the plurality of jet nozzles is configured for generating a fluid jet stream that is directed in a second jet stream direction, wherein said first and second jet stream directions are at a nonzero angle with respect to each other as seen the two-dimensional plane perpendicular to the axis of rotation, wherein, preferably, at least a third jet nozzle of the plurality of jet nozzles is configured for generating a fluid jet stream that is directed in a third jet stream direction; wherein, preferably, at least a fourth jet nozzle of the plurality of jet nozzles is configured for generating a fluid jet stream that is directed in a fourth jet stream direction; wherein, preferably, the first, second, third and/or fourth jet stream directions are at a nonzero angle with respect to each other as seen the two-dimensional plane perpendicular to the axis of rotation.

By directing the jet nozzles in multiple directions, a more continuous flushing of the rotatable cutting member is obtained. Additionally, jets in different directions can be arranged to add further technical functionality, as a jet directed towards a direction opposite to the cutting (e.g. trenching) direction can be arranged to direct the lighter sorts of cut away soils (i.e. having the smaller particles), such as sands, to be jetted to the back to directly provide a backfilling in case the trencher directly places the cable. Jets directed to the front (i.e. in the cutting direction) aid to fluidize sandy soils, such that the rotatable cutting member moves through sandy soils with less effort. Jets directed to the sides (i.e. in directions having a component perpendicular to the cutting direction) enable, even in cases when using a substantially cylindrical rotatable cutting member, to create V-trenches in a seabed having a sandy upper layer. To these ends, it is further preferred that first and second jet stream directions, and/or any other adjacent jet stream directions, are arranged at an angle between 30° and 210°, preferably between 45° and 180°, more preferably between 60° and 120°, even more preferably between 75° and 105°, most preferably around 90° with respect to each other.

Alternatively, or additionally, a number of jet nozzles of the plurality of jet nozzles can be distributed along the length, as measured along the axis of rotation, of the rotating cutting member. Accordingly, a jet nozzle row is formed. This enables, as was described above, to clean the rotatable cutting member over a section that extends at least a part, preferably the largest part, of the length of the rotatable cutting member. Importantly, the jet nozzle row enables soil transport, i.e., transport of the cut away soil to the environment. Preferably, the jetting unit comprises at least one jet nozzle row directed in a rearward direction having at least a component opposite a cutting direction of the cutting device (also referred to as “rearward jet nozzle row”), so as to provide a rearward evacuation flow in said rearward direction for evacuating the wetted soil that has been cut away by the rotatable cutting member in said rearward direction. Preferably, the rearward direction is perpendicular to the axis of rotation. The rearward evacuation flow transports cut soil away from the from the cutting zone (e.g., out of and away from a trench that is being cut into the soil). Even more preferably, the cutting device comprises at least one forward jet nozzle row, directed in a forward direction having at least a component in the cutting direction, and the rearward jet nozzle row, directed in the rearward direction. The row aimed in the cutting direction can aid in the fluidization of the soil bed (e.g., for sandy soils), and the row aimed in the rearward direction can aid in soil transport away from digging site. The cutting device may comprise a plurality of jet nozzle rows, directed in various directions.

Preferably, each jet nozzle of the plurality of jet nozzles is static with respect to the at least one cutting element. In other words, the jet nozzles do not rotate along with the at least one cutting element.

Preferably, the jetting unit comprises a jet nozzle feedpipe that extends parallel to, preferably coaxially with, the axis of rotation, and is arranged within the circumferential cutting path; wherein said jet nozzle feedpipe is in fluid connection with said at least one jet nozzle; wherein said at least one nozzle is arranged in an outer wall of said jet nozzle feedpipe. The jet nozzle feedpipe can thereby support and hold the jet nozzles at the correct position and orientation, while at the same time providing for a means of guiding the flow of pressurized fluid, in particular a pressurized liquid such as water, to an inlet side of the jet nozzle. Said jet nozzles are preferably removably mounted within said jet nozzle feedpipe, in particular in jet nozzle mounting holes, such that, in dependence of the configuration selected, different types of nozzles and/or plugs (for stopping a jet nozzle mounting hole) can be applied. Preferably, said jet nozzles are removably mounted in such a way that they can be replaced from the outside of the jet nozzle feedpipe. The jet nozzles and mounting holes can for instance be provided with cooperating threading, such that they can be screwed into the mounting holes.

It is then preferred that the jet nozzle feedpipe is a tubular member having an outer circumferential wall, wherein the at least one jet nozzle is arranged through the outer circumferential wall. In such a configuration an inlet side of the jet nozzle will extend within the jet nozzle feedpipe for receiving said flow of pressurized fluid and an outlet side of the jet nozzle extends from, or in, the outer circumferential wall in an outwardly oriented direction. It is noted that said jet nozzle feedpipe may be a segmented feedpipe, such that the nozzles may be divided a number of groups, wherein each group of nozzles is in fluid connection with a different segment of said feedpipe. In combination with, for instance, the above described different directions wherein the jet nozzles may be oriented/directed, the jet nozzles directed in a specific direction may be organized in a single group that is fed by a particular segment of said jet nozzle feedpipe. Hereby, a controller is able to control the respective jet nozzles per direction in dependence of the cutting/soil conditions.

In a preferred embodiment, the driving device preferably comprises a motor for driving the rotation of said rotatable cutting member, wherein said driving device preferably comprises a hydraulic or electric motor that is, preferably, operatively connected to the rotatable cutting member through a transfer mechanism comprising a gear box and/or flywheel. As the rotatable cutting member is a relatively stiff member that is able to take the sudden impacts due to changing soil conditions and/or running into sudden boulders, there is no need to run at relatively low capacity, as is typically done when using chain cutters. Rather, by driving the system using an electric motor (which typically runs at a relatively high speed) in combination with a gearbox, in particular having a gear ratio of less than 1, the system can be given a high rotational inertia such that it is highly suitable for forcibly cutting its way through large boulders and/or rock formations. Alternatively, or additionally, this is amplified by applying a flywheel as this further increases the inertia. The use of a flywheel thereby even leads to a high rotational inertia in case a (relatively low speed) hydraulic motor is used.

Preferably, the driving device is arranged at a first end of the rotating cutting member, as seen along the axis of rotation, and wherein the driving device is operatively coupled to the rotatable cutting member at the second, opposing, end of the rotating cutting member by means of a through axle that co-axially extends through said rotatable cutting member. It is then further preferred that jet nozzle feedpipe comprises a fluid inlet that is arranged at the first end of the rotating cutting member and wherein said through axle extends co-axially through said jet nozzle feedpipe, in particular through an internal tube that is coaxially arranged within said jet nozzle feedpipe and wherein the interior of the internal tube is not in fluid connection with said feedpipe, and is rotatably coupled to the rotatable cutting member at a second end. The driving system and fluid supply system, i.e. the jetting unit, can thereby be kept apart, such that no complicated rotating seals, that be susceptible to damage and failure, are required between the respective parts. An enhanced lifetime and reduced downtime thereby lead to a more effective cutting/trenching process.

The cutting device, preferably, comprises an evacuation system for evacuating (i.e. discarding, removing, transporting) at least a part of the wetted soil that has been cut away by the rotatable cutting member, wherein said evacuation system comprises at least one evacuation nozzle that is arranged for providing an evacuation fluid flow, i.e. evacuation stream, that is directed in an upward direction or evacuation direction, preferably at least having a component that is parallel to the axis of rotation, and more preferably wherein said component is the largest component of said direction. The rotatable cutting member moves the cut-away soil from the cutting zone (i.e. the sides of the rotatable cutting member that face the uncut soil of the respective upper section, in particular the uncut soil in the cutting/trenching direction) and the jet fluid stream(s) generated by the jet nozzle(s) flush, spray and/or jet the cut away soil away from rotatable cutting member and, secondly, aid in transporting the cut away soil from the cutting device. The jets, however, have a relatively low effectiveness in evacuating the cut away soil from a cut trench. For this purpose, an evacuation system comprising one or more evacuation nozzles can be arranged, such that the cut away soil is taken up by the evacuation flow thereby transporting it from the cutting zone and/or trench. It is in particular beneficial in case this evacuation system is combined with an embodiment wherein at least one nozzle is directed in a direction towards the one or more evacuation nozzles that are arranged for generating the evacuation fluid flow (e.g. in the backwardly oriented direction as described above), as at least a part of the cut-away soil is thereby, when flushed from the rotatable cutting member, urged towards the evacuation fluid flow that can pick up the at least a part of the cut-away soil and effectively transport it from the cutting zone and/or trench.

It is then preferred that the evacuation nozzle(s) is/are arranged, as seen in the two-dimensional plane perpendicular to the axis of rotation, outside of the circumferential cutting path and is/are, preferably, arranged, as seen in the length of the rotatable cutting member, at one of the first and second outer end sections of the rotatable cutting member and directed such that the evacuation direction comprises at least a component that is directed towards the other of the first and second outer end sections of the rotatable cutting member. Preferably, the evacuation nozzle(s) is/are arranged at the respective outer end of the cutting device that is arranged to extend the deepest, as seen from the upper surface of the upper section of soil, into the cutting zone and/or trench. The evacuation flow, that is generated by the evacuation nozzle(s), can thereby take up the cut away soil that, amongst others, is flushed out by the jet nozzle(s) and evacuate it away from the cutting device, thereby further adding to the overall effectivity of the cutting/trenching operation. The evacuation system is therefore arranged to provide a fluid flow in, preferably, the range of 0.1 - 10 m³/s at a pressure in, preferably, the range of 1 - 40 bars to the evacuation nozzle. Preferably, the pressure of the fluid flow that is supplied to the one or more evacuation nozzles is equal to, or lower than, the pressure of the fluid flow that is supplied to the at least one jet nozzle. This allows to use the same type of pump, or even the same pump, to supply the fluid flows to the at least one jet nozzle and the one or more evacuation nozzles.

Preferably, the one or more evacuation nozzles are blowing nozzles, such that the evacuation fluid flow is transported externally to the cutting device, and preferably away from the rotatable cutting member. Accordingly, no suction is required during the cutting process, thereby significantly reducing the complexity of the cutting device and increasing the efficiency of the trenching process (e.g., less maintenance and downtime). Preferably, the evacuation fluid flow aids the rearward evacuation flow of the jetting unit.

In a preferred embodiment, the rotatable cutting member is rotatably arranged in a supporting frame, wherein said supporting frame is arranged to be coupled to a subsea trenching apparatus and/or a dredging apparatus, such that the cutting member device a supporting frame that aid mounting said cutting device in the respective apparatuses such that they can be effectively used in the field.

Preferably, the evacuation system comprises evacuation guiding means for guiding the flow of evacuation fluid and cut away soil therein towards an evacuation outlet, said evacuation guiding means are preferably arranged in said supporting frame. The guiding means allow to direct the cut away soil towards predefined sections, such as directly next to the cut trench. This allows to, after the cable has been placed, to easily cover the cable by backfilling the trench. The guiding means may be arranged to deposit the evacuated cut-away soil on one side, or both sides of the cut trench, to deposit the evacuated cut away soil back into the cut trench (for instance to cover the cable that is placed in the trench, simultaneously with cutting the trench) and/or may be provided to a further transportation system, such as a suction tube, for transporting the cut away soil to a dredging and/or storage vessel. Preferably, the evacuation guiding means are movable between a deployed position and a stowed position, wherein, in the deployed position, the evacuation guiding means guide the flow of evacuation fluid and cut away soil therein in the evacuation direction, the evacuation direction having at least a component that is parallel to the axis of rotation, preferably wherein said component is the largest component of said direction.

The cutting element(s) is/are preferably a flared tooth, pick point, point attack pick, or a combination of these. Thereby the cutting element(s) can be selected on the basis of the soil that is to be cut in.

In a second aspect, the invention relates to a trenching apparatus, in particular a subsea trenching apparatus, for cutting a trench in a (wetted) ground formation, such as a seabed, comprising a cutting device according to any of the preceding embodiments, wherein, when in an operational trenching state, said axis of rotating is arranged at a non-zero angle, preferably between 30° and 90°, with respect to a top surface of the (wetted) ground formation. This enables to efficiently cut a trench in the seabed, whereby the above described advantages are obtained.

In a third aspect, the invention relates to a dredging apparatus for loosening and sucking soil from a (wetted) ground formation, such as a seabed, comprising a cutting device according to any of the preceding embodiments and a suction tube extending in the direction of the (wetted) ground formation, wherein said cutting device is arranged at the end of said suction tube for cutting away and loosening the soil that is to be sucked up by the suction tube. This enables to efficiently cut a dredge soil from the seabed, whereby the above described advantages are obtained.

In a fourth aspect, the invention relates to a method of cutting into a (wetted) ground formation, such as a seabed, using a cutting device, in particular a cutting device according to any of the preceding embodiments, wherein the method comprises the steps of:

- rotating a rotatable cutting member comprising at least one cutting element extending in at least a radially outward direction of said rotatable cutting member for engaging the (wetted) ground formation;

- engaging the (wetted) ground formation with the rotatable cutting member, in particular with the at least one cutting element;

- flushing away cut away soil from the rotatable cutting member by generating a fluid jet stream, preferably a plurality of fluid jet streams, by means of at least one jet nozzle, preferably a plurality of jet nozzles, preferably wherein each jet nozzle of the plurality of jet nozzles being static with respect to the at least one cutting element, that is/are directed in a jet stream direction that comprises at least a radial outwardly directed component that is parallel to the radial direction with respect to the axis of rotation of said rotatable cutting member, such that the at least one cutting element moves around the at least one jet nozzle and wherein, as seen in the two-dimensional plane perpendicular to the axis of rotation the fluid jet stream(s) (and therefore the jet stream direction) intersects with the circumferential cutting path, such that cut away soil is flushed from the rotating cutting member. Preferably, the method is performed without suctioning the cut away soil.

Preferably, a number of jet nozzles of the plurality of jet nozzles are distributed along the length, as measured along the axis of rotation, of the rotating cutting member, so as to form a jet nozzle row. Further preferably, the jetting unit comprises at least one jet nozzle row directed in a rearward direction having at least a component opposite a cutting direction of the cutting device, so as to provide a rearward evacuation flow in said rearward direction for evacuating the wetted soil that has been cut away by the rotatable cutting member in said rearward direction. The cutting direction may also be referred to as a progress direction, or a cutting and progress direction.

The method thereby employs the advantages provided by the cutting device as described above.

In a preferred embodiment, the method further comprises the step of:

- evacuating the wetted soil that has been cut away by the rotatable cutting member using an evacuation fluid flow that is directed in a direction at least having a component that is parallel to the axis of rotation of the rotatable cutting member, preferably wherein said component is the largest component of said direction. This enables to effectively evacuate the cut away soil from the cut area/volume, as is described above.

The present invention is further illustrated by the following figures, which show preferred embodiments of the invention, and are not intended to limit the scope of the invention in any way, wherein:

Figure 1 schematically shows, in a three-dimensional perspective, the back and side of a first embodiment of a tracked cable trenching apparatus in a deployed, e.g. cutting, state.

Figure 2 schematically shows, in a three-dimensional perspective, the back and side of the first embodiment of the tracked cable trenching apparatus in an undeployed, e.g. non-cutting, state.

Figure 3 schematically shows, in a three-dimensional perspective, a first embodiment of the cutting device as applied in the first embodiment of a tracked cable trenching apparatus..

Figure 4 schematically shows, in a three-dimensional perspective, the first embodiment of the cutting device wherein certain parts have been removed. Figures 5A - 5C schematically show in respective three-dimensional views various embodiments of a rotatable cutting member as can be used in the varies embodiments of the cutting device;

Figure 6 schematically shows a cross-sectional view of the functional layout of the cutting device according to the first embodiment.

Figure 7 schematically shows, in a three-dimensional perspective, the front of a second embodiment of a tracked cable trenching apparatus in a deployed, e.g. cutting, state.

Figure 8 schematically shows, in a three-dimensional perspective, a second embodiment of the cutting device as applied in the second embodiment of a tracked cable trenching apparatus.

Figure 9 schematically shows a cross-section of the second embodiment of the cutting device.

Figure 1 schematically shows a three-dimensional view of the back and side of a first embodiment of a tracked cable trenching apparatus 1000 in a deployed, e.g. cutting, state. The tracked cable trenching apparatus 1000 is seen to comprise a tracked vehicle 1001 that is, for instance, remotely operable from a (marine) vessel (not shown). A pair of (driven) tracks 1002 support the vehicle 1001 on the upper section of a wetted soil (i.e. the (wetted) ground formation), in particular on the seabed and are connected to the vehicle base frame 1003. A cable guiding system 1005 is arranged for guiding the cable 1 through the tracked cable trenching apparatus 1000 and a cable rear guide 1006 is arranged for guiding the cable into a trench that is dug into the seabed by the tracked cable trenching apparatus 1000. The tracked cable trenching apparatus 1000 further comprises a cutting device 100 for cutting the trench into the seabed that is movably arranged within the vehicle base frame 1003, such that the cutting device 100 is movable from a deployed, e.g. cutting, state (as is shown in figure 1), wherein the cutting device 100 is arranged for engaging the upper section of soil and cutting a trench therein, to an undeployed (i.e. resting and/or storage) state, wherein the cutting device 100 is held in an upper position, such that it is held (as seen in the vertical direction I that is substantially parallel to the seabed) above the plane spanned by the bottom surfaces of the tracks 1002, such that the cutting device 100 can be held clear from the seabed (as is seen in figure 2).

In the current example, the cutting device 100 is pivotally arranged around a pivoting shaft (not shown) that is comprised in the vehicle base frame 1003. By driving the deployment actuator 1008, which is typically a hydraulic cylinder, the cutting device 100 can be moved, i.e. pivoted, from the deployed state to the undeployed state and vice versa. The cutting device 100, as also seen in figures 3 and 4, comprises a rotatable cutting member 110 arranged to rotate around its axis of rotation III and a supporting frame 120 wherein said rotatable cutting member 110 is rotatably arranged in. During trenching, the cutting device 100 is started and brought into the deployed state, whereafter the tracked cable trenching apparatus 1000 can be driven in a cutting, or trenching, direction II.

The rotatable cutting member 110, that is driven by a hydraulic motor 130, comprises a plurality of removably mounted cutting elements 111 for engaging and cutting the soil of the upper section. In the current example the rotatable cutting member 110 is fitted with flared teeth that are the preferred option when engaging sand- and/or clay-like soils. The cutting elements 111 are seen to be mounted onto a cage-like frame member 112 comprising a plurality, in the current example four, arm members 113 that extends at a non-zero radial distance from the axis of rotation III. Coupling members and/or rings 114 are provided between said arm members 113 for connecting said arm members 113, thereby forming the substantially rigid cage-like frame member 112 that, at least in a rotating state thereof, enclose an internal (cylindrical) space 115 (as is best seen in figures 5A - 5C).

The cutting device 100 further comprises the jetting unit 140, comprising a plurality of jet nozzles 141 that are arranged, as seen in a two-dimensional plane perpendicular to the axis of rotation III, within the internal (cylindrical) space 115.

The jetting unit 140 is arranged for providing a flow of fluid to the jet nozzles 141 that are configured for generating a fluid jet stream that is directed in a jet stream direction that is radially outwardly directed with respect to the axis of rotation III. When in use, the frame member 112, comprising the cutting elements 111, moves around the jet nozzles 141 and through the thereby generated jet streams, such that cut away soil that is taken up between the respective arms 113 of the frame member 112 is washed, i.e. flushed, jetted, out of the frame member 112 and off the cutting elements 111, thereby keeping the rotatable cutting member 110 cleaner and preventing clogging of the rotatable cutting member 110. For this purpose, the jet nozzles 141 are removably arranged, for instance by means of co-operating threading, in an outer circumferential wall of a jet nozzle feedpipe 144 that is arranged within the internal (cylindrical) space 115. Depending on the desired configuration, different types of nozzles (in for instance flow speed and flow rate) may be arranged, or even stops (not shown) can be fitted in case it is desired to have no jet at the specific location. The feedpipe 144 is in fluid connection with at least one of the fluid inlets 146 that are, preferably, connected to the supporting frame. For this purpose, a fluid interconnection is made at the lower section 145 of the jet nozzle feedpipe 144, such that it is arranged on the opposite side of where the hydraulic motor 130 is operatively coupled to the rotatable cutting member 110.

As is best seen in figure 4, wherein the rotatable cutting member 110 and a hatch 151 have been left out of the figure for obtaining a better view on the other parts of the cutting device 100, the jet nozzles 141 may be arranged such that they may directed in different radially outwardly directed directions, such that, for instance, a first group 142 of jet nozzles 141 is directed in a first jet stream direction and a second group 143 of jet nozzles 141 is directed in a second jet stream direction, wherein the respective first and second jet stream directions are at a non-zero angle with respect to each other as seen the two-dimensional plane perpendicular to the axis of rotation III. A group 142, 143 of jet nozzles may be seen the jet nozzles 141 that extend in row along a direction parallel to the axis of rotation III, The jet nozzle feedpipe 144 may be segmented into different segments for this purpose, such that different groups 142. 143 of jet nozzles may be independently provided with a flow of pressurized fluid, in particular seawater taken in from the surrounding environment by a suitable pumping device that is in fluid connection with the cutting device 100. The respective segments of the feedpipe 144 may then be in fluid connection with respective different fluid inlets 146 of the cutting device 100.

The cutting device 100 further comprises an evacuation system 150 for evacuating the wetted soil that has been cut away by the rotatable cutting member 110, which comprises one or more evacuation nozzles 152 (in the current example only one (single) evacuation nozzle 152 is provided) that is arranged outside of the circumferential cutting path of the rotatable cutting member 110 and is arranged, as seen in the length of the rotatable cutting member 110, at the lower outer end section 116 for providing an evacuation fluid flow that is directed in an evacuation direction IV directed such that the main component of the evacuation direction IV is directed towards the upper outer end section 117 of the rotatable cutting member 110. The evacuation flow, that is generated by the evacuation nozzle 152, can thereby take up the cut away soil and evacuate it away from the cut trench in an upward direction.

The evacuation nozzle 152 is therefore arranged, as seen in the cutting/trenching direction II, behind the rotatable cutting member 110, where an at least upwardly directed guiding channel 153 (when in the deployed state) is arranged for guiding the evacuation flow upwards towards an evacuation system outlet 154 that is arranged substantially horizontal (at least when in the deployed state), such that the cut away soil can be deposited at the side(s) of the cut trench. The vertical guiding channel 153 and evacuation system outlet 154 can be easily cleaned from clogging soil and/or heavy boulders by opening the hatch 151 that is arranged for partially enclosing the vertical guiding channel 153 and evacuation system outlet 154 and is, preferably, mounted onto the supporting frame 120. The evacuation nozzle 152 may again be in fluid connection with one of the inlets 146 of the cutting device 100 for providing the flow of fluid, in particular sea water as described earlier.

The rotatable cutting member 110, 110b, 110c, that is interchangeably arranged withing the cutting device 110, may, depending on the soil conditions, easily be fitted with different types of cutting elements 111, such as flared teeth Illa, pick points 111b and/or point attack picks 111c, as these are removably connected. The frame member 112, 112a may also be chosen in dependence of the soil conditions. Whereas the frame member 112 comprising the straight arms 113 is simple and cheap to manufacture, the loading is more impact wise, as the cutting elements 111 will typically engage the soil to cut at substantially the same time. This loading can be made more smooth by providing, for instance, a frame member 112a having helical arms 113a. Hence, the shape of the frame member 112 may be adapted to best cope with the soil conditions on site.

Figure 6 schematically shows a cross-sectional view of the functional layout of the cutting device according to the first embodiment 100, as is discussed above. As is best seen in the functional layout, a rear group 146 of nozzles, that is composed of the jet nozzles 141 that extend in row along a direction parallel to the axis of rotation III, wherein the jet nozzles 141 of the rear group 146 are arranged for generating jet streams 147 in a direction towards the evacuation stream 155. The evacuation stream 155, that is generated by the evacuation nozzle 152, is directed in an upward direction IV. The respective jet nozzles 141 of the rear group 146 are (at least when used for cutting in the ground formation) thus directed in a backwardly-oriented direction that is directed in the direction opposite to the cutting direction II.

Figure 6 furthermore shows that the nozzles are arranged in (and through) the circumferential wall of the jet nozzle feedpipe 144, that is supplied from the lower section 145 of the jet nozzle feedpipe 144 by a flow of fluid that is provided through one of the fluid inlets 146. Another fluid inlet 146 is arranged for supplying a flow of fluid to the evacuation nozzle 152 for generating the evacuation stream 155. The rotatable cutting member 110, that is arranged to rotate around the jet nozzle feedpipe 141, is in the current embodiment coupled to the feedpipe 144 at its lower end 145 using a rotational bearing 161. Thereby, the rotatable cutting member 110 is also supported by the feedpipe Figure 7 schematically shows, in a three-dimensional perspective, the front of a second embodiment of a tracked cable trenching apparatus 2000 in a deployed, e.g. cutting, state. The tracked cable trenching apparatus 2000, which is substantially similar to tracked cable trenching apparatus 1000, is fitted with two cutting devices 200 of a second embodiment that can be arranged in a V-shape for digging a V-shaped trench. A cutting device 200 of the second embodiment is best seen in figures 8 and 9.

Cutting device 200 is substantially similar to cutting device 100 and employs a similar rotatable cutting member 210 and jetting unit 240 but differs in the following characteristics. The lower, or outer, end section 216 of the rotatable cutting member 200 is not externally supported by the supporting frame 220, such that it is only supported on the upper end section 217. This allows it to be operated in a substantially vertical orientation, i.e. perpendicular to the surface of the seabed, as there is no part of the supporting frame 220 extending beyond the lower end section 216 that needs to be accounted for, as is the case for cutting device 100. This allows to trench to a deeper depth with a rotatable cutting member 210 of the same size. The outer end section 216 can rather be supported by the lower end 245 of the jet nozzle feedpipe 241 by providing a bearing therebetween.

The rotatable cutting member 210 is driven by an electric motor 230 that is coupled to a low-ratio gearbox 231 (i.e. ratio < 1) for obtaining a drive with a high rotational inertia. The drive shaft, i.e. axle, 232 extending between, i.e. rotationally coupling, the gearbox and rotatable cutting member 210 runs co-axially through said jet nozzle feedpipe 241 and is coupled to the rotatable cutting member 210 by means of, for instance, a spline connection. This allows to arrange the fluid inlet 246 and its fluid connection to the feedpipe 241 at the upper end 246 of the feedpipe 241, near the motor 230 and gearbox 231, while not requiring any complex rotating seals to separate the fluid flow from the driving parts.

The present invention is not limited to the embodiment shown, but extends also to other embodiments falling within the scope of the appended claims.

Claims

1. Cutting device arranged for cutting into a wetted ground formation, such as a seabed, said device comprising a:

- wherein the cutting device comprises a jetting unit, comprising a plurality of jet nozzles, each jet nozzle of the plurality of jet nozzles being static with respect to the at least one cutting element, wherein said jetting unit is arranged for providing a flow of fluid to the plurality of jet nozzles, wherein each of said plurality of jet nozzles is arranged, as seen in a two-dimensional plane perpendicular to the axis of rotation, within the circumferential cutting path and is configured for generating a fluid jet stream that is directed in a jet stream direction that comprises at least a radial outwardly directed component that is parallel to the radial direction with respect to the axis of rotation of said rotatable cutting member, such that, when in use, the at least one cutting element moves around the plurality of jet nozzles and wherein, as seen in the two-dimensional plane perpendicular to the axis of rotation, each fluid jet stream intersects with the circumferential cutting path, wherein a number of jet nozzles of the plurality of jet nozzles are distributed along the length, as measured along the axis of rotation, of the rotating cutting member, so as to form a jet nozzle row and wherein the jetting unit comprises at least one jet nozzle row directed in a rearward direction having at least a component opposite a cutting direction of the cutting device, so as to provide a rearward evacuation flow in said rearward direction for evacuating the wetted soil that has been cut away by the rotatable cutting member in said rearward direction.

2. Cutting device according to claim 1, wherein the rotatable cutting member comprises a frame member comprising at least one arm member, wherein said arm member extends at a radial distance from the axis of rotation in at least an axial direction and holds said at least one cutting element; wherein, when rotating, said frame member delimits an internal space of said rotatable cutting member and wherein the plurality of jet nozzles are arranged within said internal space.

3. Cutting device according to claim 2, wherein said frame member comprises a plurality of arm members, wherein each arm member extends at a radial distance from the axis of rotation in at least an axial direction and holds at least one cutting element; wherein, when the frame member comprises three arms or more, the frame member is substantially cage-like shaped; wherein the arm members are preferably evenly spaced apart, as seen along the azimuth direction with respect to the axis of rotation.

4. Cutting device according to at least claim 2, when rotating, said frame member defines, in at least a rotating state, a circumferential surface delimiting an external volume and wherein said external volume is shaped as, or to comprise, a substantially uniform cylinder, a substantially non- uniform cylinder, such as a cone or frusto-cone, a hemi-dome like shape, or a combination of these.

5. Cutting device according to any of the preceding claims, wherein the length of the rotatable cutting member, as measured along the axis of rotation, is larger than the largest radius of a circumferential cutting path of a cutting element, preferably larger than 2 times the largest radius of a circumferential cutting path of a cutting element, more preferably larger than 3 times the largest radius of a circumferential cutting path of a cutting element, most preferably larger than 5 times the largest radius of a circumferential cutting path of a cutting element.

6. Cutting device according to any of the preceding claims, wherein at least a first jet nozzle of the plurality of jet nozzles is configured for generating a fluid jet stream that is directed in a first jet stream direction and at least a second jet nozzle of the plurality of jet nozzles is configured for generating a fluid jet stream that is directed in a second jet stream direction, wherein said first and second jet stream directions are at a non-zero angle with respect to each other as seen the two- dimensional plane perpendicular to the axis of rotation, wherein, preferably, at least a third jet nozzle of the plurality of jet nozzles is configured for generating a fluid jet stream that is directed in a third jet stream direction; wherein, preferably, at least a fourth jet nozzle of the plurality of jet nozzles is configured for generating a fluid jet stream that is directed in a fourth jet stream direction; wherein, preferably, the first, second, third and/or fourth jet stream directions are at a nonzero angle with respect to each other as seen the two-dimensional plane perpendicular to the axis of rotation.

7. Cutting device according to claim 6, wherein said first and second jet stream directions, and/or any other adjacent jet stream directions, are arranged at an angle between 30° and 210°, preferably between 45° and 180°, more preferably between 60° and 120°, even more preferably between 75 and 105°, most preferably around 90° with respect to each other.

8. Cutting device according to any of the preceding claims, wherein the rearward direction is perpendicular to the axis of rotation.

9. Cutting device according to any of the preceding claims, wherein the jetting unit comprises a jet nozzle feedpipe for guiding the flow of fluid, wherein the feedpipe extends parallel to, preferably co-axially with, the axis of rotation, and is arranged within the circumferential cutting path; wherein said jet nozzle feedpipe is in fluid connection with at least one jet nozzle of the plurality of jet nozzles; wherein said at least one jet nozzle is arranged in an outer wall of said jet nozzle feedpipe.

10. Cutting device according to claim 9, wherein said jet nozzle feedpipe is a tubular member having an outer circumferential wall, wherein the at least one jet nozzle is arranged through the outer circumferential wall.

11. Cutting device according to any of the preceding claims, comprising a driving device comprising a motor for driving the rotation of said rotatable cutting member, wherein said driving device preferably comprises a hydraulic or electric motor that is, preferably, operatively connected to the rotatable cutting member through a transfer mechanism comprising a gear box and/or flywheel.

12. Cutting device according to claim 11, wherein the driving device is arranged at a first end of the rotating cutting member, as seen along the axis of rotation, and wherein the driving device is operatively coupled to the rotatable cutting member at the first end of the rotating cutting member and wherein, preferably, the jet nozzle feedpipe comprises a fluid inlet that is also arranged at the first end of the rotating cutting member.

13. Cutting device according to claim 11, wherein the driving device is arranged at a first end of the rotating cutting member, as seen along the axis of rotation, and wherein the driving device is operatively coupled to the rotatable cutting member at the second, opposing, end of the rotating cutting member by means of a through axle that co-axially extends through said rotatable cutting member.

14. Cutting device according to at least claims 9 and 13, wherein said jet nozzle feedpipe comprises a fluid inlet that is arranged at the first end of the rotating cutting member and wherein said through axle extends co-axially through said jet nozzle feedpipe, in particular through an internal tube that is coaxially arranged within said jet nozzle feedpipe and wherein the interior of the internal tube is not in fluid connection with said feedpipe, and is rotatably coupled to the rotatable cutting member at a second end.

15. Cutting device according to any of the preceding claims, wherein the cutting device comprises an evacuation system for evacuating the wetted soil that has been cut away by the rotatable cutting member, wherein said evacuation system comprises one or more evacuation nozzles that are arranged for providing an evacuation fluid flow that is directed in an evacuation direction, the evacuation direction preferably having at least a component that is parallel to the axis of rotation, and more preferably wherein said component is the largest component of said direction.

16. Cutting device according to claim 15, wherein said single or multiple evacuation nozzles are arranged, as seen in the two-dimensional plane perpendicular to the axis of rotation, outside of the circumferential cutting path and are, preferably, arranged, as seen in the length of the rotatable cutting member, at one of the first and second outer end sections of the rotatable cutting member and directed such that that the evacuation direction comprises at least a component that is directed towards the other of the first and second outer end sections of the rotatable cutting member.

17. Cutting device according to claim 15 or 16, wherein the one or more evacuation nozzles are blowing nozzles, such that the evacuation fluid flow is directed away from the rotatable cutting member.

18. Cutting device according to any of the preceding claims, wherein the rotatable cutting member is rotatably arranged in a supporting frame, wherein said supporting frame is arranged to be coupled to a subsea trenching apparatus and/or a dredging apparatus.

19. Cutting device according to at least claim 15, wherein the evacuation system comprises evacuation guiding means for guiding the flow of evacuation fluid and cut away soil therein towards an evacuation outlet, said evacuation guiding means are preferably arranged in said supporting frame.

20. Cutting device according to claim 19, wherein the evacuation guiding means are movable between a deployed position and a stowed position, wherein, in the deployed position, the evacuation guiding means guide the flow of evacuation fluid and cut away soil therein in the evacuation direction, the evacuation direction having at least a component that is parallel to the axis of rotation, preferably wherein said component is the largest component of said direction.

21. Cutting device according to any of the preceding claims, wherein the cutting element(s) is/ are a flared tooth, pick point, point attack pick, or a combination of these.

22. Cutting device according to any of the preceding claims, wherein the jet stream direction of at least one, preferably each, of the plurality jet nozzles is directed substantially entirely radially outward, substantially parallel to the radial direction with respect to the axis of rotation of said rotatable cutting member.

23. Cutting device according to any of the preceding claims, wherein at least one, preferably each, jet nozzle of the plurality of jet nozzles is arranged radially outwardly, substantially perpendicular to the axis of rotation of the rotatable cutting member.

24. Trenching apparatus, in particular a subsea trenching apparatus, for cutting a trench in a wetted ground formation, such as a seabed, comprising a cutting device according to any of the preceding claims, wherein, when in an operational trenching state, said axis of rotating is arranged at a nonzero angle, preferably between 30° and 90°, with respect to a top surface of the wetted ground formation.

25. Dredging apparatus for loosening and sucking soil from a wetted ground formation, such as a seabed, comprising a cutting device according to any of the preceding claims 1 - 23 and a suction tube extending in the direction of the wetted ground formation, wherein said cutting device is arranged at the end of said suction tube for cutting away and loosening the soil that is to be sucked up by the suction tube.

26. Method of cutting into a wetted ground formation, such as a seabed, using a cutting device, in particular a cutting device according to any of the preceding claim 1 - 23, wherein the method comprises the steps of:

- rotating a rotatable cutting member comprising at least one cutting element extending in at least a radially outward direction of said rotatable cutting member for engaging the wetted ground formation;

- engaging the wetted ground formation with the rotatable cutting member, in particular with the at least one cutting element; - flushing away cut away soil from the rotatable cutting member, by generating a plurality of fluid jet streams, by means of a plurality of jet nozzles, each jet nozzle of the plurality of jet nozzles being static with respect to the at least one cutting element, that are each directed in a jet stream direction that comprises at least a radial outwardly directed component that is parallel to the radial direction with respect to the axis of rotation of said rotatable cutting member, such that the at least one cutting element moves around the plurality of jet nozzles and wherein, as seen in the two- dimensional plane perpendicular to the axis of rotation each of the fluid jet streams intersects with the circumferential cutting path, such that cut away soil is flushed from the rotating cutting member, wherein a number of jet nozzles of the plurality of jet nozzles are distributed along the length, as measured along the axis of rotation, of the rotating cutting member, so as to form a jet nozzle row, and wherein the jetting unit comprises at least one jet nozzle row directed in a rearward direction having at least a component opposite a cutting direction of the cutting device, so as to provide a rearward evacuation flow in said rearward direction for evacuating the wetted soil that has been cut away by the rotatable cutting member in said rearward direction.

27. Method of cutting into a wetted ground formation according to claim 26, further comprising the step of:

- evacuating the wetted soil that has been cut away from the wetted ground formation by the rotatable cutting member using an evacuation fluid flow that is directed in an evacuation direction, preferably wherein the evacuation direction at least has a component that is parallel to the axis of rotation, and more preferably wherein said component is the largest component of said direction.