Trench cutter

Abstract

A trenching device (1). The trenching device (1) comprises: a main body (11); one or more fluid pressurising means; a trench-forming jetting tool (14) extending from the main body (11) and comprising one or more primary jetting outlets (15) along a length of the trench-forming jetting tool (14); a first fluid flow path (41) extending between at least one of the one or more fluid pressurising means and the one or more primary jetting outlets (15); a jetting arm (16), an end of the jetting arm (16) being connected to the main body (11), the jetting arm (16) comprising one or more secondary jetting outlet (165); and a second fluid flow path (166) extending between at least one of the one or more fluid pressurising means and the one or more secondary jetting outlet (165); The trenching device (1) has: a primary jetting configuration in which the trenching device (1) is operable to eject fluid from the one or more primary jetting outlets (15) at a first pressure, to cut or fluidise material adjacent the trench-forming jetting tool (14) to form a trench (TR); and a secondary jetting configuration in which the trenching device (1) is operable to eject fluid from the one or more secondary jetting outlet (165) at a second pressure, to cut or fluidise material adjacent to the one or more secondary jetting outlet (165), the second pressure being greater than the first pressure.

Description

[0001] TRENCH CUTTER

[0002] The present invention relates to a trenching device. In particular, but not exclusively, the present invention relates to a trenching device with a primary jetting configuration and a secondary jetting configuration.

[0003] The formation of trenches in the ground is a well-known requirement and is typically used for burying utility supply means, for example, oil, gas and water pipes, and electricity and telecommunication cables. In underwater environments, the cutting of a trench is often used for burial of pipes and cables and usually utilises specially constructed or adapted equipment configured for underwater conditions, for example the nature of the seabed. Herein “seabed” is used to refer to the bed of a body of water such as the sea or of a lake or even a river, unless otherwise specified.

[0004] A wide variety of cable laying and burial equipment is available and can be selected depending on the environment and specific needs (e.g. seabed conditions and burial depth). Various apparatus for constructing a trench and laying a cable or pipe are known in the art. These can include soil cutting devices in the form of plough share, jetting apparatus, and mechanical cutters (for example chain cutters). Jetting is generally suitable for soft or loose soils, whilst mechanical cutting is generally suitable for hard or dense soils, for example those with a high clay content. The soil cutting device may be mounted on a device that moves over the ground or floor (e.g. the seabed) either under its own power or by external means. For example, the trench cutting device might be towed by a tractor vehicle or by a ship at the surface of the sea, or the trench cutting device may be an integral part of a tractor unit.

[0005] When trench cutting using jetting, hard or dense soils are sometimes encountered. This can slow down, or even stall, trench. In order to overcome this problem, it is known to use a mechanical cutter to cut through the hard material. However, changing the cutters (i.e. from a jetting apparatus to a mechanical cutter) slows down trench cutting progress, especially because it is necessary to install or use guards to protect the item being laid from the mechanical cutter. Furthermore, mechanical cutters are often too heavy to fit to smaller jet cutting vehicles meaning that the entire vehicle and host vessel must be substituted for a mechanical cutting vehicle. Clearly then, encountering hard material in an otherwise soft seabed material is detrimental to achieving an efficient and economical trench cutting operation.

[0006] It would be advantageous to overcome at least some of these limitations. According to a first aspect of the present invention there is provided a trenching device, for example a trenching device, comprising: a main body; one or more fluid pressurising means; a trench-forming jetting tool extending from the main body and comprising one or more, e.g., a plurality of, primary jetting outlets along a length of the trench-forming jetting tool; a first fluid flow path extending between at least one of the one or more fluid pressurising means and the one or more primary jetting outlets; a jetting arm, an end of the jetting arm being connected to the main body, the jetting arm comprising one or more, e.g., a plurality of, secondary jetting outlet / s; and a second fluid flow path extending between at least one of the one or more fluid pressurising means and the one or more secondary jetting outlet; wherein the trenching device has: a primary jetting configuration in which the trenching device is operable to eject fluid from the one or more primary jetting outlets at a first pressure, to cut or fluidise material adjacent the trench-forming jetting tool to form a trench; and a secondary jetting configuration in which the trenching device is operable to eject fluid from the one or more secondary jetting outlet at a second pressure, to cut or fluidise material adjacent to the one or more secondary jetting outlet, the second pressure being greater than the first pressure.

[0007] That is, the trenching device is operable in each of a primary jetting configuration and a secondary jetting configuration.

[0008] As used herein an 'arm' is a structure that projects from a larger structure. For example in the context of the described trenching device a jetting arm projects from the main body of the trenching device.

[0009] The jetting arm may be deployable. That is, the jetting arm may be configured to be deployed for operation of the trenching device in the secondary jetting configuration.

[0010] The trenching device may be an underwater or subsea trenching device. The fluid may be water from a body of water surrounding the trenching device, in use. The trench-forming jetting tool may be a jet sword. Advantageously, the trench-forming jetting tool provides means to form a trench in, for example, soft clay or sand, and the one or more secondary jetting outlet provides means to focus cutting or fluidising at the location of the one or more secondary jetting outlet. The one or more secondary jetting outlet is usable, for example, when hard or compacted material is encountered, which the primary jetting outlets are unable to cut or fluidise efficiently, or at all.

[0011] The trenching device may be operable in the secondary jetting configuration independently of the primary jetting configuration.

[0012] In the primary jetting configuration, the first fluid flow path may be open and the respective one or more of the at least one fluid pressurising means may be operational.

[0013] In the secondary jetting configuration, the second fluid flow path may be open and the respective one or more of the at least one fluid pressurising means may be operational.

[0014] In the primary jetting configuration, the second fluid flow path may be closed and / or the respective one or more of the at least one fluid pressurising means may not be operational.

[0015] The trenching device may comprise or may be in communication with a controller. The controller may be configured to: when the trenching device is operating in the primary jetting configuration, determine a parameter which is indicative of the rate at which the trench is being formed by the trenchforming jetting tool; determine if the parameter is below a rate threshold; and if the parameter is below the rate threshold, output a notification or instruction that the trenching device should be operated in the secondary jetting configuration.

[0016] The notification(s) may be outputted to a user interface. The notification may instruct or suggest to an operator that the trenching device be operated in the secondary jetting configuration.

[0017] The instruction may be a part of an automated system. The instruction may cause the trenching device to continue to operate in the primary jetting configuration.

[0018] In certain embodiments, if the parameter is at or above the rate threshold, the controller may be configured to output a notification or instruction that the trenching device should continue to be operated in the primary jetting configuration. The parameter may be a rate at which the trench is formed, e.g., the length of trench formed per unit of time or the time required to progress the trench over a predetermined distance. The rate at which the trench is formed may be measured by measuring a speed of the trenching device along the floor.

[0019] The parameter may be a first parameter. The rate threshold may be a first rate threshold.

[0020] The controller may be further configured to: when the trenching device is operating in the secondary jetting configuration, determine a second parameter which is indicative of the rate at material is cut or fluidised by the one or more secondary jetting outlets; determine if the second parameter is at or above a second rate threshold; and if the parameter is at or above the second rate threshold, output a notification or instruction.

[0021] The notification may be that the trenching device should be operated in the primary jetting configuration. The notification may be sent to an operator via a user interface. The instruction may be a part of an automated system. The instruction may cause the trenching device to operate in the primary jetting configuration.

[0022] In certain embodiments, if the parameter is below the second rate threshold, the controller may be configured to output a notification or instruction that the trenching device should continue to operate in the secondary jetting configuration.

[0023] The notification(s) may be outputted to a user interface. The notification may instruct or suggest to an operator that the trenching device continue to be operated in the secondary jetting configuration.

[0024] The instruction may be a part of an automated system. The instruction may cause the trenching device to continue to operate in the secondary jetting configuration.

[0025] The trenching device may be used in an automated system. The trenching device may automatically change from the secondary jetting configuration to the first jetting configuration, and / or vice versa, based on the or an instruction. The second parameter may be a rate at which material is cut or fluidised by ejecting fluid from the one or more secondary jetting outlets, e.g., the volume of material cut or fluidised by ejecting fluid from the one or more secondary jetting outlets per unit of time.

[0026] The rate at which the trench is being formed by the trench-forming jetting tool and / or the rate at which material is cut or fluidised by ejecting fluid from the one or more secondary jetting outlets may be measured or estimated by one or more sensors which are in communication with the controller. The sensors may be accelerometers and / or cameras and / or pressure sensors and / or load cells and / or any other suitable feedback means.

[0027] The trench-forming jetting tool may be rotatably mounted to the main body, such that the trenchforming jetting tool is rotatable about one or more axes. One of the one or more axes may be substantially horizontal when the trenching device is located on a horizontal surface. One of the one or more axes may be perpendicular to a central axis of the trench-forming jetting tool. One of the one or more axes may be perpendicular to a central axis of the trench-forming jetting tool such that the trench-forming jetting tool is rotatable between a stowed position and a trench cutting position. One of the one or more axes may be substantially vertical when the trenching device is located on a horizontal surface.

[0028] The plurality of primary jetting outlet may comprise nozzles, for example water nozzles. The one or more secondary jetting outlets may comprise nozzles, for example water nozzles.

[0029] The secondary jetting outlets may be rotatably mounted to the jetting arm such that they are rotatable relative to the jetting arm.

[0030] The first fluid flow path may be provided by a first conduit. The second fluid flow path may be provided by a second conduit. The first and second conduits may both be in fluidic communication with one fluid pressurising means. The first and second conduits may be connected to common outlet conduit connected to one of the fluid pressurising means. The first and second conduits may be connected to a common outlet conduit connected to one of the fluid pressurising means at a two-way valve. The first conduits may extend along the trench-forming jetting tool. The second conduit may extend along the jetting arm.

[0031] The second conduit may have a diameter of less than 500 mm, for example between 100 mm and 300 mm. The second conduit may comprise a plurality of pipe sections connected together by rotatable joints. The second conduit may comprise a hose, e.g., a flexible hose. The one or more fluid pressurising means may comprise a first fluid pressurising means and a second fluid pressurising means. The first fluid flow path may extend between the first fluid pressurising means and the one or more primary jetting outlets. The second fluid flow path may extend between the second fluid pressurising means and the one or more secondary jetting outlets.

[0032] The second fluid flow path may extend between the first fluid pressurising means and the second fluid pressurising means, such that, when the trenching device is operated in the secondary jetting configuration, fluid flows from the first fluid pressurising means to the second fluid pressurising means along the second fluid flow path, and then flows from the second fluid pressurising means to the one or more secondary jetting outlets, along the second fluid flow path. The second fluid flow path may be partially provided by a third conduit extending between the first fluid pressurising means and the second fluid pressurising means. Advantageously the first fluid pressurising means may act as a primer for the second fluid pressurising means.

[0033] The first fluid pressurising means may be a first pump. The second fluid pressurising means may be a second pump. The second fluid pressurising means may be a fluid intensifier.

[0034] For example, the fluid intensifier has an inlet which receives fluid flow at a relatively low pressure and at a relative high flow rate, and output which outputs fluid at a relatively high pressure and at a relatively low flow rate.

[0035] The trenching device may comprise a turbine in fluidic communication with the first pump and mechanically coupled to the fluid intensifier. The turbine may be configured to be driven by fluid flow from the first pump to drive the fluid intensifier.

[0036] The trenching device may comprise at least one valve, e.g., an actuated valve, a solenoid valve or a diver-operated valve, located in the second fluid flow path. When the trenching device is operated in the primary jetting configuration, the at least one valve may prevent fluid flow along the second fluid flow path. Advantageously, the second fluid pressurising means is shielded from the first pressure.

[0037] The trenching device may comprise at least one valve, e.g., a solenoid valve, located in the first fluid flow path. When the trenching device is operated in the secondary jetting configuration, the at least one valve may prevent fluid flow along the first fluid flow path. The trench forming jetting tool may extend from the main body at a first position of the main body. The jetting arm may be connected to the main body at a second position which is separate to, e.g., which is spaced from, the first position.

[0038] The second position may be at, or be proximal to, a front of the trenching device, when in use. Advantageously, when hard material is encountered, the jetting arm may be used to cut or fluidise the hard material ahead of the presently formed trench.

[0039] The jetting arm may be movable between a stowed configuration and an operational configuration. For operation in the secondary jetting configuration the jetting arm may be in the operational configuration.

[0040] Advantageously, the jetting arm may be stowed so that it does not interfere with cable laying operations in the primary jetting configuration.

[0041] The jetting arm may be an articulating arm. Advantageously, the one or more secondary jetting outlets may be positioned to focus the ejected fluid at specific, e.g., hard, material.

[0042] The jetting arm may comprise a plurality of arm sections connected together by rotatable joints. An end of one of the arm sections may be mounted to the main body. The jetting arm may comprise an actuator associated with each rotatable joint, each actuator being configured to be actuated to rotate at least one of the arm sections attached to the respective rotatable joint about the respective rotatable joint. There may be 2, 3, 4, 5, 6 or more arm sections. Advantageously, the jetting arm may be capable of complex movements.

[0043] In the stowed configuration the arm sections may be substantially parallel with one another in a stacked arrangement. Advantageously, the jetting arm may occupy a small footprint when in the or a stowed configuration.

[0044] At least one of the one or more secondary jetting outlets may be mounted to the arm section which is furthest from the arm section which is mounted to the main body. The one or more of, e.g., all of the plurality of, secondary jetting outlets may be mounted to the arm section which is furthest from the arm section which is mounted to the main body. The jetting arm may be rotatably mounted to the main body. The trenching device may comprise an actuator connected between the jetting arm and the main body. The actuator may be configured to be actuatable to move the jetting arm relative to the main body.

[0045] The first pressure may be less than 20 bar, for example between 4 and 16 bar. The second pressure may be less than 150 bar, for example between 12 and 120 bar.

[0046] According to a second aspect of the invention there is provided a method of forming an underwater or subsea trench, the method comprising: providing a trenching device on a floor in which the trench is to be formed; operating the trenching device in a primary jetting configuration in which material is cut or fluidised adjacent to a trench-forming jetting tool which extends from a main body of the trenching device and into the floor to form the trench, wherein cutting or fluidising material adjacent the trench-forming jetting tool is by ejecting fluid, at a first pressure, from one or more, e.g., a plurality of, primary jetting outlets arranged along a length of the trenchforming jetting tool; operating the trenching device in a secondary jetting configuration wherein material is cut or fluidised adjacent to one or more secondary jetting outlets of a jetting arm of the trenching device, an end of the jetting arm being connected to the main body of the trenching device, wherein cutting or fluidising material adjacent the one or more secondary jetting outlets is by ejecting fluid, at a second pressure which is greater than the first pressure, from the one or more secondary jetting outlets.

[0047] Advantageously, the method allows the trenching operation to continue without requiring the deployment of a separate vehicle, such as a mechanical trenching device.

[0048] Again, as used herein an 'arm' is a structure that projects from a larger structure. For example in the context of the described trenching device a jetting arm projects from the main body of the trenching device.

[0049] The fluid may be water from a body of water surrounding the trenching device. The trench-forming jetting tool may be a jet sword.

[0050] The method may comprise: when operating in the primary jetting configuration, determining a parameter which is indicative of the rate at which the trench is being formed by the trench-forming jetting tool; determining if the parameter is below a rate threshold; if the parameter is at or above the rate threshold, continuing to operate the trenching device in the primary jetting configuration; and if the parameter is below the rate threshold, operating the trenching device in the secondary jetting configuration.

[0051] The parameter may be a rate at which the trench is formed, e.g., the length of trench formed per unit of time. The rate at which the trench is formed may be determined by the speed at which the trenching device progresses along the floor.

[0052] The method may comprise: when operating in the secondary jetting configuration, determining a second parameter which is indicative of the rate at material is cut or fluidised by the one or more secondary jetting outlets; determining if the second parameter is above a second rate threshold; if the parameter is below the second rate threshold, continuing to operate the trenching device in the secondary jetting configuration; and if the parameter is at or above the second rate threshold, operating the trenching device in the primary jetting configuration.

[0053] The second parameter may be a rate at which material is cut or fluidised by ejecting fluid from the one or more secondary jetting outlets, e.g., the volume of material cut or fluidised by ejecting fluid from the one or more secondary jetting outlets per unit of time.

[0054] The rate at which the trench is being formed by the trench-forming jetting tool and / or the rate at which material is cut or fluidised by ejecting fluid from the one or more secondary jetting outlets may be measured or estimated by one or more sensors which are in communication with the controller. The sensors may be accelerometers and / or cameras and / or pressure sensors and / or load cells and / or any other suitable feedback means.

[0055] The trenching device may be operated in the secondary jetting configuration independently of the primary jetting configuration.

[0056] Ejecting fluid from the one or more primary jetting outlets may be by moving fluid, using a first fluid pressurising means, along a first fluid flow path extending between the first fluid pressurising means and the primary jetting outlets. Ejecting fluid from the one or more secondary jetting outlets may be by moving fluid, using a second fluid pressurising means, along a second fluid flow path extending between the second fluid pressurising means and the one or more secondary jetting outlet.

[0057] The second fluid flow path may extend between the first fluid pressurising means and the second fluid pressurising means. Ejecting fluid from the one or more secondary jetting outlet may be by moving fluid from the first fluid pressurising means along the second fluid flow path to the second fluid pressurising means, and then moving fluid along the second fluid flow path from the second fluid pressurising means to the one or more secondary jetting outlet. Advantageously the first fluid pressurising means may act as a primer for the second fluid pressurising means.

[0058] When ejecting fluid from the one or more primary jetting outlets, fluid may be prevented from flowing along a second fluid flow path to the one or more secondary jetting outlet by closing at least one valve located in the second fluid flow path.

[0059] When ejecting fluid from the one or more secondary jetting outlet, fluid may be prevented from flowing along a first fluid flow path to the one or more primary jetting outlets by closing at least one valve located in the first fluid flow path.

[0060] When the trenching device is operated in the secondary jetting configuration, the method may comprise moving the one or more secondary jetting outlet relative to the main body of the trenching device, to position the one or more secondary jetting outlet adjacent to material to be cut or fluidised.

[0061] When the trenching device switches from operating in the primary jetting configuration to the secondary jetting configuration, the jetting arm may be moved from a stowed configuration to an operational configuration, in which the one or more secondary jetting outlet is positioned adjacent to material to be cut or fluidised.

[0062] According to a third aspect of the invention there is provided a jetting arm for attachment to a trenching device, the jetting arm comprising: an articulating arm; at least one rotatable joint along the length of the articulating arm; an actuator associated with each of the at least one rotatable joint, each actuator being configured to be actuated to move at least part of the articulating arm about the respective rotatable joint, to move the water jetting outlet relative to the mounting means; a mounting means for mounting the articulating arm to the trench cutting vehicle; a plurality of water jetting outlets attached to the articulating arm; and a conduit extending along the articulating arm, the conduit having a conduit connector at a first end and being connected to the plurality of water jetting outlets, the conduit connector for connecting the conduit to a water pressurising means.

[0063] The mounting means may be located at an end of the articulating arm.

[0064] Again, as used herein an 'arm' is a structure that projects from a larger structure. For example in the context of the described trenching device a jetting arm projects from the main body of the trenching device.

[0065] The articulating arm may comprise a plurality of arm sections connected together by rotatable joints. An end of one of the arm sections may comprise the mounting means. The jetting arm may comprise an actuator associated with each rotatable joint, each actuator being configured to be actuated to rotate at least one of the arm sections attached to the respective rotatable joint about the respective rotatable joint. There may be 2, 3, 4, 5, 6 or more arm sections.

[0066] The jetting arm may comprise a main actuator associated with the mounting means, the main actuator being configured to be actuated to move the articulating arm relative to the trenching device when the jetting arm is attached to the trenching device.

[0067] The jetting arm may be movable between a stowed configuration and an operational configuration. In the stowed configuration the arm sections may be substantially parallel with one another in a stacked arrangement.

[0068] The plurality of water jetting outlets may be mounted to the arm section which is furthest from the mounting means.

[0069] According to a fourth embodiment of the invention there is provided a jet cutting system comprising the aforementioned jetting arm and a water pressurising means, the water pressurising means having an inlet and an outlet connected or connectable to the conduit connector.

[0070] For the avoidance of doubt, any of the features described herein apply equally to any aspect of the invention. For example, the trenching device may comprise any one or more features of the jetting arm and / or the method may comprise any one or more features or steps relevant to one or more features of the trenching device or the jetting arm.

[0071] A further aspect of the invention provides a computer program element comprising computer readable program code means for causing a processor to execute a procedure to implement one or more steps of the aforementioned method.

[0072] A yet further aspect of the invention provides the computer program element embodied on a computer readable medium.

[0073] A yet further aspect of the invention provides a computer readable medium having a program stored thereon, where the program is arranged to make a computer execute a procedure to implement one or more steps of the aforementioned method.

[0074] A yet further aspect of the invention provides a control means or control system or controller comprising the aforementioned computer program element or computer readable medium.

[0075] Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. For the avoidance of doubt, the terms “may”, “and / or”, “e.g.”, “for example” and any similar term as used herein should be interpreted as non-limiting such that any feature so-described need not be present. Indeed, any combination of optional features is expressly envisaged without departing from the scope of the invention, whether or not these are expressly claimed. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner.

[0076] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:

[0077] Figure 1 is a schematic of a trenching device according to a first embodiment of the invention;

[0078] Figure 2 is a schematic of a jetting arm of the trenching device of Figure 1 , in an operational configuration; Figure 3 is a schematic of the jetting arm of Figure 2, in a stowed configuration;

[0079] Figure 4 is a schematic of the jetting arm of Figure 2 with a conduit extending along the jetting arm;

[0080] Figure 5 is a schematic of a trenching device according to a second embodiment of the invention;

[0081] Figure 6 is a front view of the trenching device of either Figure 1 or Figure 4;

[0082] Figure 7 is a schematic of a first embodiment of pressurising means for use in a trenching device;

[0083] Figure 8 is a schematic of a second embodiment of pressurising means for use in a trenching device;

[0084] Figure 9 is a schematic of a third embodiment of pressurising means for use in a trenching device;

[0085] Figure 10 is a schematic of a fourth embodiment of pressurising means for use in a trenching device; and

[0086] Figure 11 is a schematic of a fifth embodiment of pressurising means for use in a trenching device.

[0087] Figure 1 shows a trenching device 1 , which in this example is a subsea trenching device. The trenching device 1 is for forming a trench TR and, in this example, laying an elongate product E into the trench TR. The elongate product E may be a pipe or cable. The trenching device 1 has a main body 11 and one or more fluid pressurising means (not shown), which are subsequently referred to broadly as “pressurising means”. The pressurising means has one of multiple configurations, for example including one or more pumps, or a fluid intensifier, and the different configurations are discussed subsequently with reference to Figures 7 to 11. Any of these pressurising means are usable in the trenching device 1 of this example.

[0088] In this example the main body 11 is connected to a surface vessel (not shown) by a tether T, and the trenching device 1 has continuous tracked wheels 12 for moving the trenching device 1 along a seabed, or floor F. It will be appreciated that the trenching device may instead, or also, have skids for moving along the floor F. The trenching device 1 is propelled along the floor F by any suitable means, such as by driving the tracks of the tracked wheels 12 or by towing the trenching device 1 . In use, the trenching device 1 moves along the floor F in a forward direction X.

[0089] In this example the trenching device 1 has a depressor 13 pivotably connected to the main body 11 and located at the rear of the trenching device 1 , when in use. The depressor 13 provides a predetermined radius of curvature to the elongate product E while pushing the elongate product E into the trench TR, in use.

[0090] The trenching device 1 has a trench-forming jetting tool 14 extending from a first position on the main body 11 . In this example the trench-forming jetting tool 14 is pivotably mounted to the main body 11 such that it is movable, along arrow 14M shown in Figure 1 , between a stowed position 14S and a trench cutting, deployed, or operational position 14D. In this example the trenchforming jetting tool 14 is pivotable about a first axis A1 which is substantially horizontal when the trenching device 1 is positioning on a horizontal floor F. In this example, the trenching device 1 has a main actuator 17, connected to an end of the trench-forming jetting tool 14, for rotating the trench-forming jetting tool 14 around the first axis A1. Whilst the trench-forming jetting tool 14 is shown in both the stowed position 14S and an operational position 14D in Figure 1 , it will be appreciated that this is the same trench-forming jetting tool 14. That is, there is only one trenchforming jetting tool 14 in the example shown in Figure 1 .

[0091] In this example the trench-forming jetting tool 14 is formed of two, parallel members, as best seen in Figure 6. In this example, the trench-forming jetting tool 14 has a plurality of primary jetting outlets 15 along a length of the trench-forming jetting tool 14. It will be appreciated that any number of primary jetting outlets 15 may be provided, including just one. In this example, the plurality of jetting outlets 15 are located along each parallel member of the trench-forming jetting tool 14. The primary jetting outlets 15 are connected to the pressurising means via a first fluid flow path 141 , as best shown in Figure 6.

[0092] The trenching device 1 has a jetting arm 16. A first end 16a of the jetting arm 16 is connected to the main body 11 at a second position which is separate to the first position. In this example the second position is at or near to the front of the main body 11 , with respect to the forward direction X. In this example the first end 16a of the jetting arm 16 is connected to the main body 11 by a rotatable connection. In this example, the rotatable connection allows rotation about a second axis A2 and about a third axis A3, although it would be understood that the jetting arm 16 may be rotatable about just one of the second or third axis A2, A3. Alternatively, the rotatable connection may allow rotation about other axis, or the rotatable connection may be a universal joint, thereby allowing rotation about any axis. Alternatively, the jetting arm 16 may be connected to the main body 11 by a fixed connection, i.e., a connection that is not rotatable. The second axis A2 is substantially horizontal when the trenching device 1 is on a horizontal floor F and is parallel to the forward direction X of the trenching device 1 , in use. The third axis A3 is substantially vertical when the trenching device 1 is on a horizontal floor F. In this example the trenching device 1 has a first actuator (not shown) for rotating the jetting arm 16 about the second axis A2, and a second actuator (not shown) for rotating the jetting arm 16 about the third axis A3. As used herein an 'arm' is a structure that projects from a larger structure. For example in the context of the described trenching device the jetting arm 16 projects from the main body 11 of the trenching device 1.

[0093] Referring now to Figures 2 and 3, with continued reference to Figure 1 , the jetting arm 16 of this example is shown. In this example the jetting arm 16 has a plurality of arm sections 161a, 161 b, 161c connected by rotatable joints 162a, 162b. In this example the number of arm sections 161a, 161 b, 161c is three, but any number can be used. The jetting arm 16 has a jetting arm actuator 163a, 163b associated with each rotatable joint 162a, 162b. The jetting arm actuators 163a, 163b are not shown in Figure 3. In use, actuation of one of the jetting arm actuators 163a, 163b causes one of the arm sections 161a, 161 b connected to the corresponding rotatable joint 162a, 162b to rotate relative to the other arm section 161a, 161 b connected to the rotatable joint 162a, 162b.

[0094] In this example, each jetting arm actuator 163a, 163b is connected at one end to a respective one of the arm sections 161a, 161 b, and is connected at the other end to a linkage 164a, 164b. Each linkage has a first rod connected at one end to an end of a second rod, the connection between the first and second rods also being connected to the respective jetting arm actuator 163a, 163b. The other end of the first rod is connected to the arm section 161 b, 161c which the respective jetting arm actuator 163a, 163b is also connected to. The other end of the second rod is connected to the other of the respective arm sections 161 b, 161c connected to the respective rotatable joint 162a, 162b. This type of linkage may be referred to as a bucket linkage.

[0095] When one of the jetting arm actuators 163a, 163b is actuated, by lengthening or shortening the jetting arm actuator 163a, 163b, the corresponding linkage is rotated about the connection with the arm section 161a, 161 b, such that the other arm section 161a, 161 b connected to the same rotatable joint 162a, 162b is rotated about the rotatable joint 162a, 162b. In this way, the jetting arm 16 is an articulating arm. The jetting arm 16 is movable between a stowed configuration, as is shown in Figure 3, and an operational configuration, as is shown in Figure 2. In the stowed configuration, the arm sections 161a, 161 b, 161 c are substantially parallel with one another in a stacked arrangement. In the stowed or operational configuration, the jetting arm 16 may be rotated around the second axis A2 such that the stacked or deployed arm sections 161a, 161 b, 161c rotate away from the floor F, or the jetting arm 16 may remain in a substantially horizontal orientation (when the trenching device 1 is on a horizontal floor F), as shown in Figure 3. In this example the jetting arm 16 has a plurality of secondary jetting outlets 165, only one of which is visible. In this example, the secondary jetting outlets are located on the arm section which is furthest from the main body 11 . At least one of the secondary jetting outlets is located proximal the end of the arm section which is furthest from the main body 11 . Although only one secondary jetting outlet 165 is visible in Figures 1 to 3, this is for illustration only, and any number of secondary jetting outlets 165 may be provided.

[0096] A second fluid flow path 166, which is shown schematically with dashed lines in Figure 2, extends between the pressurising means and the secondary jetting outlets 165. In this example the second fluid flow path is provided by a conduit (not shown) extending along the length of the jetting arm 16. The conduit may be of any suitable type, such as a flexible hose. The conduit may otherwise be provided by a plurality of pipe sections 171a, 171 b, 171c connected together by rotatable joints 172a, 172b, as shown in Figure 4.

[0097] In this example, each of these joints 172a, 172b is formed of a short pipe section with elbow joints at either end, the elbow sections connected to the pipe sections 171a, 171 b, 171c associated with the particular joint. The elbow sections are rotatable relative to the short pipe section. The conduit is orientated such that an axis of the short pipe section of each joint 172a, 172b is substantially perpendicular to the axis of the corresponding rotatable joint 162a, 162b of the jetting arm 16. In this way, when one arm section 161a, 161 b, 161c of the jetting arm is rotated about the respective rotatable joint 162a, 162b relative to the other respective arm section 161a, 161 b, 161c, the associated pipe sections and elbows rotate relative to the short pipe section of the corresponding rotatable joint 172a, 172b of the conduit. In all examples of conduit, the conduit has a connector at the end furthest from the secondary jetting outlets 165, for connection to further pipework or hoses which provide a flow path between the pressurising means and the conduit.

[0098] Alternatively, the conduit may extend through the arm sections 161a, 161 b, 161c of the jetting arm 16. That is, the arm sections 161a, 161 b, 161c may be provided as tube or conduits, such that fluid flows through the arm sections 161a, 161 b, 161c. In this case, rotatable joints such as those shown in Figure 4 may be implemented to provide fluid flow between adjacent arm sections 161a, 161 b, 161c.

[0099] In operation the trenching device 1 has a primary jetting configuration and a second jetting configuration. In the primary jetting configuration, the trenching device 1 is operable to eject fluid from the plurality of primary jetting outlets 15 at a first pressure P1. The fluid is pressurised by the pressurising means, moved along the first fluid flow path and ejected to cut or fluidise material adjacent the trench-forming jetting tool 14 to form the trench TR. As the material adjacent the trench-forming jetting tool 14 is cut or fluidised the trenching device 1 progresses along the forward direction X and lays the elongate product E into the trench TR using the depressor 13.

[0100] In the secondary jetting configuration, the trenching device 1 is operable to eject fluid from the secondary jetting outlets at a second pressure P2. The fluid is pressurised by the pressurising means, moved along the second fluid flow path and ejected from the secondary jetting outlets to cut or fluidise material adjacent to the secondary jetting outlets. The second pressure P2 is greater than the first pressure P1. In this example the first pressure P1 is from about 4 bar to about 16 bar, and the second pressure P2 is from about 12 bar to about 120 bar. For example, the second pressure P2 may be between 4 and 11 bar and the second pressure may be between 12 and 120 bar. By way of another example the first pressure P1 may be between 4 and 16 bar and the second pressure P2 between 17 and 120 bar. In this example, the trenching device 1 is operable in the second jetting configuration independently of the primary jetting configuration, and vice versa.

[0101] In this example, to bring the trenching device 1 to the secondary jetting configuration, the jetting arm 16 is deployed from the stowed position shown in Figure 3, to an operational position such as that shown in Figure 2. In this way, hard or compacted material, which the primary jetting outlets 15 are unable to cut or fluidise, can be cut of fluidised by focusing the fluid ejected from the secondary jetting outlets at the second pressure P2. Once the material to be cut or fluidised at the second pressure P2 has been cut or fluidised, the jetting arm 16 is retracted back to the stowed position shown in Figure 3. In this example, the jetting arm 16 is deployed form the stowed position by actuating the first actuator and second actuator, and the jetting arm actuators 163a, 163b.

[0102] In this example, the trenching device 1 includes, or is in communication with, means, for example a controller or control system, for determining a parameter which is indicative of the rate at which the trench TR is being formed by the trench-forming jetting tool 14 in the primary jetting configuration. In this example the parameter is the rate at which the trench TR is being formed, for example the length of trench TR formed per unit of time. Other parameters may include the pressure in the trench TR adjacent the trench-forming jetting tool 14, or an upstream pressure of the first fluid flow path which is used to indicate the pressure in the trench TR adjacent the trenchforming jetting tool 14. When operating the trenching device 1 in the primary jetting configuration, the parameter is determined. If the parameter is determined to be at or above a rate threshold, the trenching device 1 continues to be operated in the primary jetting configuration. If the parameter is determined to be below the rate threshold, a notification is output, for example to a user interface, indicating to an operator that the trenching device 1 should be operated in the secondary jetting configuration. The operator then switches the trenching device 1 to the secondary jetting configuration. In other examples, the trenching device may operate on an automate system, and instead of a notification an instruction may be sent to the automated system to operate the trenching device in the secondary jetting configuration.

[0103] In this example, the means, or controller, is also for determining a second parameter, which is indicative of the rate at material is cut or fluidised by the one or more secondary jetting outlet in the secondary jetting configuration. In this example the second parameter is a rate at which material is cut or fluidised by ejecting fluid from the secondary jetting outlets, e.g., the volume of material cut or fluidised by ejecting fluid from the secondary jetting outlets per unit of time. Other parameters may include the pressure in the trench TR adjacent the second jetting outlets 165, or an upstream pressure of the second fluid flow path which is used to indicate the pressure in the trench TR adjacent the second jetting outlets 165. When operating the trenching device 1 in the secondary jetting configuration, if the second parameter is determined to be below a second rate threshold, then the trenching device 1 continues to be operated in the secondary jetting configuration. If the second parameter is determined to be above the second rate threshold, a notification is output, for example to the user interface, indicating to the operator that the trenching device 1 should be operated in the primary jetting configuration. The operator then switches the trenching device 1 to the primary jetting configuration. Otherwise, an instruction may be sent to the automated system to switch the trenching device to the primary jetting configuration.

[0104] The rate at which the trench is being formed by the trench-forming jetting tool and / or the rate at which material is cut or fluidised by ejecting fluid from the one or more secondary jetting outlets may be measured or estimated by one or more sensors which are in communication with the controller. The one or more sensors may be accelerometers and / or cameras and / or pressure sensors and / or load cells and / or any other suitable feedback means. For example the one or more sensors may include a camera (not shown) located on the main body 11 or on the trenchforming jetting tool 14. Alternatively, or in addition, the one or more sensors may include a pressure sensor (not shown) for measuring one or more pressures in the trench TR adjacent the trench-forming jetting tool 14 or the jetting arm 16.

[0105] By way of example, one of many possible operational scenarios is that the trenching device 1 is laying the elongate produce E in a relatively soft material such as sand, with a parameter at or above the rate threshold, until the trench-forming jetting tool 14 encounters compacted or hard material such as a hard clay. If this causes the parameter to drop to below the rate threshold, the trenching device 1 would switch to the secondary jetting configuration. In the secondary jetting configuration, the jetting arm 16 would be deployed such that the hard or compacted material is cut or fluidised by the fluid ejected from the secondary jetting outlets at the second pressure P2. Once the second parameter goes to above the second rate threshold then the trenching device 1 switches back to the primary jetting configuration and the jetting arm 16 is moved to the stowed position.

[0106] It would be understood that other modes of operation are possible. For example, when operated in the primary jetting configuration, if the parameter is determined to be below the rate threshold, the trenching device 1 may be switched to the second jetting configuration for a predetermined amount of time before being switched back to the primary jetting configuration.

[0107] Referring now to Figure 5, a second embodiment of a trenching device 2 is shown. The trenching device 2 of this embodiment is similar to the trenching device 1 of Figure 1 , and similar features are denoted with the same reference numbers as in Figure 1 but starting with ‘2’ instead of T. The trenching device 2 of this embodiment differs from the trenching device 1 of the previous embodiment in that the jetting arm 26 has six arm sections 261 a-f, instead of the three arm sections 161 a-c of the trenching device 1 of the previous embodiment. These arm sections 261a- f have associated linkages, actuators 263a-e, and rotatable joints 262a-e, as in the previous embodiment, and the operation of the jetting arm 26, and the trenching device 2, is the same as described in the previous embodiment. Figure 4 shows the jetting arm 26 in the stowed position 26S and in the deployed position 26D, but it will be appreciated that this is for illustration only, and this merely shows two positions of the jetting arm 26. That is, the trenching device 2 only has one jetting arm 26. Whilst the jetting arm 26 of this embodiment is more cumbersome and complex than the jetting arm 16 with three arm sections 161 a-c of the previous embodiment, the jetting arm 26 of this embodiment has a greater range of available movements due to the additional rotatable joints 262d, 262e, as well it being possible to make the arm sections 261 a-f longer whilst still occupying a similar footprint when stacked in the stowed position 26S.

[0108] Figure 6 shows a front view of the trenching device 1 , 2 according to either of the previous embodiments. As can be seen, the first end 16a, 26a of the jetting arm 16, 26 is mounted to the main body 11 , 21 at a position offset from the centreline. This is so that the jetting arm 16, 26 does not obstruct a path of the elongate product E. Figure 6 shows an arc 0 which extends across the width of the trench TR, by rotating the jetting arm 16, 26 about a combination of the second axis A2 and the third axis A3. This allows the secondary jetting outlets to reach all positions across the width of the trench TR or the width of the trench TR which will be formed.

[0109] Referring now to Figure 7 an example pressurising means 4 is shown. The pressurising means 4 has a first fluid pressurising means 41 and a second fluid pressurising means 46 which is separate to the first fluid pressurising means 41. The first fluid pressurising means 41 has a first pump 42 which is driven by a first motor 43, e.g., an electric motor. The first fluid pressurising means 41 has a first inlet 44, providing fluid flow to the first pump 42, and a first outlet 45 providing fluid flow from the first pump 42. The first inlet 44 provides a part of the first fluid flow path of the trenching device. The first outlet 45 is in fluidic communication with the plurality of primary jetting outlets.

[0110] The second fluid pressurising means 46 has a second pump 47 which is driven by a second motor 48, e.g., an electric motor. The second fluid pressurising means 46 has a second inlet 49, providing fluid flow to the second pump 47, and a second outlet 410 providing fluid flow from the second pump 47. The second inlet 49 provides a part of the second fluid flow path of the trenching device. The second outlet 410 is in fluidic communication with the secondary jetting outlets.

[0111] When the trenching device using this first example of a pressurising means 4 is operated in the primary jetting configuration, fluid, preferably water from the body of water surrounding the trenching device, is drawn through the first inlet 44 by the first pump 42 which is being driven by the first motor 43. The first pump 42 thereby pressurises the fluid to substantially the first pressure P1 (which is the first pressure P1 plus any losses occurring between the first pump 42 and the plurality of primary jetting outlets) to be delivered, along the first fluid outlet 45, to the plurality of primary jetting outlets. In the primary jetting configuration, the second pump 47 is stationary, that is, the second pump 47 is not being driven by the second motor 48. Therefore, there is no, or there is negligible, flow along the second fluid flow path.

[0112] When the trenching device using this first example of a pressurising means 4 is operated in the secondary jetting configuration, fluid, preferably water from the body of water surrounding the trenching device, is drawn through the second inlet 49 by the second pump 47 which is being driven by the second motor 48. The second pump 47 thereby pressurises the fluid to substantially the second pressure P2 (which is the second pressure P2 plus any losses occurring between the second pump 47 and the secondary jetting outlets) to be delivered, along the second fluid outlet 410, to the secondary jetting outlets. In the secondary jetting configuration, the first pump 42 may continue to be operated to pump fluid to the plurality of primary jetting outlets, or may be stationary such that there is no, or there is negligible, fluid flow along the first fluid flow path. This first example of pressurising means 4 is usable in any of the embodiments of trenching device described previously.

[0113] Referring now to Figure 8, a second example of a pressurising means 5 is shown. This pressurising means 5 is similar to the pressurising means 4 of the previous example and similar features are denoted starting with ‘5’ instead of ‘4’. This pressurising means 5 differs from the pressurising means 4 of the previous example in that the second fluid inlet 59 is connected to the first fluid outlet 55.

[0114] When the trenching device, which has the pressurising means 5 of this example, is operated in the secondary jetting configuration the first pump 52 pressurises fluid to the first pressure P1 , this pressurised fluid then flows along the first outlet 55 to the plurality of primary jetting outlets and along the second inlet 59 to the second pump 57. In this way, the first pump 52 acts as a primer for the second pump 57. The second pump 57 then pressurises the fluid to substantially the second pressure P2 to be delivered to the secondary jetting outlets.

[0115] As in the previous example, when the trenching device, which has the pressurising means 5 of this example, is operated in the primary jetting configuration, the second pump 57 is stationary such that no, or negligible, fluid flows along the second fluid flow path.

[0116] This second example of pressurising means 5 is usable in any of the embodiments of trenching device described previously.

[0117] Referring now to Figure 9, a third example of a pressurising means 6 is shown. This pressurising means 6 is similar to the pressurising means 5 of the previous example and similar features are denoted starting with '6’ instead of ‘5’. This pressurising means 6 differs from the pressurising means 5 of the previous example in that a first valve 611 is located in the first fluid outlet 65 and a second valve 612 is located in the second fluid inlet 69. The second fluid inlet 69 is connected to the first fluid outlet 65 at a position between the first pump 62 and the first valve 611. In this example the first and second valves 611 , 612 are solenoid valves, being configurable in an open position, where they allow fluid to flow through, or a closed position, where they prevent fluid flowing through.

[0118] When the trenching device, which has the pressurising means 6 of this example, is operated in the primary jetting configuration, the first valve 611 is open and the second valve 612 is closed, thereby preventing fluid flow from the first pump 62 along the second inlet 69. As in the previous examples, the second pump 67 is stationary, but the second valve 612 removes the requirement that the second pump 67 withstands an inlet pressure at the first pressure P1 , caused by the first pump 62, as is the case in the pressurising means 5 of the previous example.

[0119] When the trenching device, which has the pressurising means 6 of this example, is operated in the secondary jetting configuration, the second valve 612 is open and the first valve 611 is either left open, allowing fluid flow to also be provided to the plurality of primary jetting outlets, or is closed, so that all fluid flow from the first pump 62 is provided to the second pump 67.

[0120] This third example of pressurising means 6 is usable in any of the embodiments of trenching device described previously.

[0121] Referring now to Figure 10 a fourth example of a pressurising means 7 is shown. This pressurising means 7 is similar to the pressurising means 6 of the previous example and similar features are denoted starting with 'T instead of ‘6’. This pressurising means 7 differs from the pressurising means 6 of the previous example in that the second fluid pressurising means 76 has a fluid intensifier 77 instead of a pump. The fluid intensifier 77 receives fluid at the first pressure P1 and at a first flow rate, and outputs the fluid at the second pressure at a second flow rate, which is lower than the first flow rate. The fluid intensifier 77 is driven by a turbine 78. The second inlet 79 is connected to the first fluid outlet 75 via the second valve 712, as in the example of Figure 9, the second inlet 79 providing the fluid inlet to the fluid intensifier 77. The second inlet 79 also provides fluid to drive the turbine 78, the turbine 78 then mechanically driving the fluid intensifier. As with the second pump 67 of the previous example, the fluid intensifier 77 pressurises the fluid to the second pressure P2 in the second outlet 710. The turbine 78 has a turbine outlet 713 which is optionally connected to an energy recovery system, to reduce the losses associated with a high-speed discharge. In this example, the flow is slowed in a diffuser, which is an expanding conical section.

[0122] When the trenching device, which has the pressurising means 7 of this example, is operated in the primary jetting configuration, the first valve 711 is open and the second valve 712 is closed, thereby preventing fluid flow from the first pump 72 along the second inlet 79. This means that the turbine 78 does not receive driving power, and so the fluid intensifier 77 does not operate.

[0123] When the trenching device, which has the pressurising means 7 of this example, is operated in the secondary jetting configuration, the second valve 712 is open and the first valve 711 is either left open, allowing fluid flow to also be provided to the plurality of primary jetting outlets, or is closed, so that all fluid flow from the first pump 72 is provided to the fluid intensifier 77 and to the turbine 78 to drive the fluid intensifier 77. Fluid flowing through the turbine 78 flows through the turbine outlet 713 and is either discharged, for example back to the body of water, or goes through an energy recovery system.

[0124] This fourth example of pressurising means 7 is usable in any of the embodiments of trenching device described previously.

[0125] Referring now to Figure 11 , a fifth example of pressurising means 8 is shown. In this example there is only one pressurising means 81 , which is the same as the first fluid pressurising means 41 of Figure 7, with similar features denoted starting with ‘8’ instead of ‘4’. In this example, fluid is provided by the pump 82 to the plurality of primary jetting outlets and to the secondary jetting outlets. A first valve 811 is provided between the plurality of primary jetting outlets and the pump 82, and a second valve 812 is provided between the secondary jetting outlets and the pump 82.

[0126] When the trenching device, which has the pressurising means 8 of this example, is operated in the primary jetting configuration, the second valve 812 is closed such that fluid is only provided to the plurality of primary jetting outlets and the pump 82 is operated with an output at substantially the first pressure P1 .

[0127] When the trenching device, which has the pressurising means 8 of this example, is operated in the secondary jetting configuration, the second valve 812 is open, the first valve 811 is closed, and the pump 82 is operated with an output at substantially the second pressure P2, such that fluid is provided to the secondary jetting outlet.

[0128] In any of the examples of pressurising means of Figures 9 to 13, whilst one pump is shown in the first fluid pressurising means, there may be any number. For example, multiple pumps may be provided which are connected together in series, or each pump may provide fluid flow to any number of the primary jetting outlets. Furthermore, whilst in Figures 9 to 12 one pump or fluid intensifier is shown in the second fluid pressurising means, any number of pumps or fluid intensifiers may be provided.

[0129] In another embodiment of the invention, a jetting arm, such as those described with reference to Figures 1 to 5, is provided with a mounting means for mounting the jetting arm to the trench cutting vehicle. A conduit extending along the jetting arm has a conduit connector at a first end, for connection to a pressurising means of the trenching device, the pressurising means being one of those described earlier. In this way, the jetting arm may be retrofitted to a trenching device.

[0130] It will be appreciated by those skilled in the art that features of the described embodiments may be combined. It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and / or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.

Claims

CLAIMS1 . A trenching device comprising: a main body; one or more fluid pressurising means; a trench-forming jetting tool extending from the main body and comprising one or more primary jetting outlets along a length of the trench-forming jetting tool; a first fluid flow path extending between at least one of the one or more fluid pressurising means and the one or more primary jetting outlets; a jetting arm, an end of the jetting arm being connected to the main body, the jetting arm comprising one or more secondary jetting outlet; and a second fluid flow path extending between at least one of the one or more fluid pressurising means and the one or more secondary jetting outlet; wherein the trenching device has: a primary jetting configuration in which the trenching device is operable to eject fluid from the one or more primary jetting outlets at a first pressure, to cut or fluidise material adjacent the trench-forming jetting tool to form a trench; and a secondary jetting configuration in which the trenching device is operable to eject fluid from the one or more secondary jetting outlet at a second pressure, to cut or fluidise material adjacent to the one or more secondary jetting outlet, the second pressure being greater than the first pressure.

2. A trenching device according to claim 1 , wherein the trenching device is operable in the secondary jetting configuration independently of the primary jetting configuration.

3. A trenching device according to either of claim 1 or claim 2, comprising a controller, the controller configured to: when the trenching device is operating in the primary jetting configuration, determine a parameter which is indicative of the rate at which the trench is being formed by the trench-forming jetting tool; determine if the parameter is below a rate threshold; and if the parameter is below the rate threshold, output a notification or instruction that the trenching device should be operated in the secondary jetting configuration.

4. A trenching device according to claim 3, wherein the parameter is a rate at which the trench is formed, e.g., the length of trench formed per unit of time.

5. A trenching device according to either of claim 3 or claim 4, wherein the controller is further configured to: when the trenching device is operating in the secondary jetting configuration, determine a second parameter which is indicative of the rate at material is cut or fluidised by the one or more secondary jetting outlet; determine if the second parameter is at or above a second rate threshold; and if the parameter is at or above the second rate threshold, output a notification or instruction that the trenching device should be operated in the primary jetting configuration.

6. A trenching device according to claim 5, wherein the second parameter is a rate at which material is cut or fluidised by ejecting fluid from the one or more secondary jetting outlet, e.g., the volume of material cut or fluidised by ejecting fluid from the one or more secondary jetting outlet per unit of time.

7. A trenching device according to any preceding claim, wherein the one or more fluid pressurising means comprises a first fluid pressurising means and a second fluid pressurising means, and wherein: the first fluid flow path extends between the first fluid pressurising means and the one or more primary jetting outlets; and the second fluid flow path extends between the second fluid pressurising means and the one or more secondary jetting outlet.

8. A trenching device according to claim 7, wherein the second fluid flow path extends between the first fluid pressurising means and the second fluid pressurising means, such that, when the trenching device is operated in the secondary jetting configuration, fluid flows from the first fluid pressurising means to the second fluid pressurising means along the second fluid flow path and, then flows from the second fluid pressurising means to the one or more secondary jetting outlet, along the second fluid flow path.

9. A trenching device according to claim 8, wherein the first fluid pressurising means is a first pump, and the second fluid pressurising means is a second pump or is a fluid intensifier.

10. A trenching device according to any preceding claim, comprising at least one valve located in the second fluid flow path wherein, when the trenching device is operated in the primaryjetting configuration, the at least one valve prevents fluid flow along the second fluid flow path.

11. A trenching device according to any preceding claim, comprising at least one valve located in the first fluid flow path and wherein, when the trenching device is operated in the secondary jetting configuration, the at least one valve prevents fluid flow along the first fluid flow path.

12. A trenching device according to any preceding claim, wherein the trench forming jetting tool extends from the main body at a first position on the main body, and the jetting arm is connected to the main body at a second position which is separate to the first position.

13. A trenching device according to claim 12, wherein the second position is at a front of the trenching device, when in use.

14. A trenching device according to any preceding claim, wherein the jetting arm is movable between a stowed configuration and an operational configuration, wherein, for operation in the secondary jetting configuration the jetting arm is in the operational configuration.

15. A trenching device according to any preceding claim, wherein the jetting arm is an articulating arm.

16. A trenching device according to any preceding claim, wherein the jetting arm comprises a plurality of arm sections connected together by rotatable joints, wherein an end of one of the arm sections is mounted to the main body and wherein the jetting arm comprises an actuator associated with each rotatable joint, each actuator being configured to be actuated to rotate at least one of the arm sections attached to the respective rotatable joint about the respective rotatable joint.

17. A trenching device according to claim 16, wherein the jetting arm is movable between a stowed configuration and an operational configuration, wherein in the stowed configuration the arm sections are substantially parallel with one another in a stacked arrangement.

18. A trenching device according to either of claim 16 or claim 17, wherein at least one of the one or more secondary jetting outlet is mounted to the arm section which is furthest from the arm section which is mounted to the main body.

19. A trenching device according to any preceding claim, wherein the jetting arm is rotatably mounted to the main body, and wherein the trenching device comprises an actuator connected between the jetting arm and the main body, the actuator being configured to be actuated to move the jetting arm relative to the main body.

20. A trenching device according to any preceding claim, wherein the first pressure is between 4 and 16 bar, and the second pressure is between 12 and 120 bar.21 . A method of forming an underwater or subsea trench, the method comprising: providing a trenching device on a floor in which the trench is to be formed; operating the trenching device in a primary jetting configuration in which material is cut or fluidised adjacent to a trench-forming jetting tool which extends from a main body of the trenching device and into the floor to form the trench, wherein cutting or fluidising material adjacent the trench-forming jetting tool is by ejecting fluid, at a first pressure, from one or more primary jetting outlets arranged along a length of the trench-forming jetting tool; operating the trenching device in a secondary jetting configuration wherein material is cut or fluidised adjacent to one or more secondary jetting outlet of a jetting arm of the trenching device, an end of the jetting arm being connected to the main body of the trenching device, wherein cutting or fluidising material adjacent the one or more secondary jetting outlet is by ejecting fluid, at a second pressure which is greater than the first pressure, from the one or more secondary jetting outlet.

22. A method according to claim 21 , comprising: when operating in the primary jetting configuration, determining a parameter which is indicative of the rate at which the trench is being formed by the trench-forming jetting tool; determining if the parameter is below a rate threshold; if the parameter is at or above the rate threshold, continuing to operate the trenching device in the primary jetting configuration; andif the parameter is below the rate threshold, operating the trenching device in the secondary jetting configuration.

23. A method according to claim 22, wherein the parameter is a rate at which the trench is formed, e.g., the length of trench formed per unit of time.

24. A method according to any of claim 22 to claim 23, comprising: when operating in the secondary jetting configuration, determining a second parameter which is indicative of the rate at material is cut or fluidised by the one or more secondary jetting outlet; determining if the second parameter is above a second rate threshold; if the parameter is below the second rate threshold, continuing to operate the trenching device in the secondary jetting configuration; and if the parameter is at or above the second rate threshold, operating the trenching device in the primary jetting configuration.

25. A method according to claim 24, wherein the second parameter is a rate at which material is cut or fluidised by ejecting fluid from the one or more secondary jetting outlet, e.g., the volume of material cut or fluidised by ejecting fluid from the one or more secondary jetting outlet per unit of time.

26. A method according to any of claim 18 to claim 22, wherein the trenching device is operated in the secondary jetting configuration independently of the primary jetting configuration.

27. A method according to any of claim 21 to claim 26, wherein ejecting fluid from the one or more primary jetting outlets is by moving fluid, using a first fluid pressurising means, along a first fluid flow path extending between the first fluid pressurising means and the primary jetting outlets, and wherein ejecting fluid from the one or more secondary jetting outlet is by moving fluid, using a second fluid pressurising means, along a second fluid flow path extending between the second fluid pressurising means and the one or more secondary jetting outlet.

28. A method according to claim 27, wherein the second fluid flow path extends between the first fluid pressurising means and the second fluid pressurising means and wherein ejecting fluid from the secondary jetting outlet is by moving fluid from the first fluid pressurisingmeans along the second fluid flow path to the second fluid pressurising means, and then moving fluid along the second fluid flow path from the second fluid pressurising means to the one or more secondary jetting outlet.

29. A method according to any of claim 21 to claim 28, wherein, when ejecting fluid from the one or more primary jetting outlets, fluid is prevented from flowing along a second fluid flow path to the one or more secondary jetting outlet by closing at least one valve located in the second fluid flow path.

30. A method according to any of claim 21 to claim 29, wherein, when ejecting fluid from the one or more secondary jetting outlet, fluid is prevented from flowing along a first fluid flow path to the one or more primary jetting outlets by closing at least one valve located in the first fluid flow path.31 . A method according to any of claim 21 to claim 30, wherein, when the trenching device is operated in the secondary jetting configuration, the method comprises moving the one or more secondary jetting outlet relative to the main body of the trenching device, to position the one or more secondary jetting outlet adjacent to material to be cut or fluidised.

32. A method according to any of claim 21 to claim 31 , wherein, when the trenching device switches from operating in the primary jetting configuration to the secondary jetting configuration, the jetting arm is moved from a stowed configuration to an operational configuration, in which the one or more secondary jetting outlet is positioned adjacent to material to be cut or fluidised.

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