The present invention relates to a backfill device for a trencher and a method of backfilling. In embodiments the invention relates to a device for backfilling a subsea trench although the invention is applicable more broadly to trenches whether subsea or not.

There are many known trenching machines for digging trenches in land or on the seabed by use of a prime mover such as a crawler tractor, or a conventional tractor pulling a trailer, in which a cutting device is positioned in the trench on a boom. The main examples are a cutting rotor rotating about an axis transverse to the trench, known as a ripper cutter, or one or more cutting rotors rotating about an axis aligned along the length of the boom, generally known as a milling cutter, or a cutting device having an elongate endless support means carrying a plurality of cutting elements and trained along upper and lower runs on the boom, known as a chain cutter. Where a cutting rotor is used this is mounted on the distal end of a boom projecting forwardly and downwardly from the prime mover, relative to the direction of digging of the trench. Where a chain cutter is used, this is normally mounted on a boom extending downwardly and rearwardly from the prime mover relative to the direction of cutting of the trench.

Examples of such trenching machines are found in, for example, CH-A-239498, WO-A-95/13433, WO-A-03/044286, US-A-6,467,201, EP-A-080,802, CN-A-2010 50077, CN-A-2517789, GB-A-786,829, WO-A-2007/035,400, JP-H04169696, US-A-5,540,006, GB-A-972,208, GB-A-848,277, GB-A-735,116, US-A-6,470,607, GB-A-1,118,907, GB-A- 2,088,930, GB-A-155,766, GB-A-2,551,419 and WO-A-2012/123,622.

Depending on the eventual purpose of the trench, it can sometimes be desired to fill the trench or “backfill” the trench after it has been formed. For example, in the case of a trench that has been formed for housing a cable or pipe for the transfer of some utility, it is typically desirable to backfill the trench after the cable or pipe have been placed within it. Although improvements in such devices are desired generally, a particular need exists for a backfill attachment for a trencher that can be arranged with or fitted to a subsea trencher or another vehicle. Typically, one known way of backfilling a trench is with the use of a cutting boom or chain laid on its side arranged to pull the spoil inwards towards the trench, thereby filling it. However, a problem with such arrangements is that the chain is subject to high wear since it is necessary to keep the chain tight so as to avoid the chain inadvertently coming out of its guide. The chain will typically be arranged in a slot or gulley in a cutting boom.

There are known devices that are provided for the backfilling of trenches. For example, WO-A-2020/148,514 discloses a plough that is used to backfill a trench.

US-A-3,807,067 discloses a continuously longitudinally moveable mainframe that is positionable at a longitudinally extending ditch having a continuously longitudinally extending mound of filler earth stacked transversely adjacent the ditch. The mainframe mounts three spaced rotatable augers extending horizontally and transversely of the ditch and vertically actuated tamper following each auger engaged with filler earth in the ditch, or followed by a rotatable sweeper brush. During movement of the mainframe, the augers are appropriately engaged with the mount of filler earth, moving the earth into the ditch while the tampers compact the filler earth within the ditch and the brush sweeps excess filler earth to the ditch.

Further examples of backfilling machines are described in US-A-5,479,728, USA-6266900 which discloses a trenching device including a backfill mechanism which is in the form of a wiper.

WO-A-2007/126,890 discloses a combined trencher and backfill device that includes an auger. The arrangement comprises an auger assembly and a digging chain rotatably connected to a trenching boom. The auger is arranged to rotate faster than if it were driven simply by the digging chain of the device, allowing the auger to have a smaller diameter than might typically be expected. GB2405882 discloses a trench filling machine including two augers. US3807067 discloses a device comprising spiral augers coupled to a machine. DE3631543 discloses a machine including front and rear augers.

According to a first aspect of the present invention, there is provided a trenching and backfill device, comprising: a trenching machine arranged to cut a trench in the ground; a first auger and a second auger arranged coupled or couplable to the trenching machine and driven so as to drive earth from the dug trench back into the trench to thereby backfill the trench. As used herein “earth” and “ground” may refer to soil or material that is removed in the formation of a trench on land or subsea.

Preferably, the first and second augers are arranged at acute angles relative to the longitudinal direction of the trench. Preferably the angle is variable by use of control or dive means (not shown herein).

Preferably, the first and second augers are arranged overlapped such that in use the entire width of the trench is covered by one or both of the augers. In other words, in a direction transverse to the longitudinal axis of the trench, the augers cover it completely. This ensures a reliable and complete fill of the trench in operation.

Preferably, the augers have a housing having an open front and underside to expose the thread of the augers to the earth formation.

Preferably, the augers are rotated in such a manner so as to cause the thread of the augers to undercut the earth being moved. This is a particularly advantageous arrangement. Due to the direction of rotation of the threads the teeth (when present) on the threads of the augers cut up into the formation or the earth or seabed with which they are engaged. This means that there is natural bias in operation that forces the augers downwards and reduces the risk of them lifting above the surface which can lead to a failure to engage with the desired material.

Preferably, the backfill device comprises a frame coupled to a prime mover. This enables the backfill device to be decoupled and connected to a different prime mover if desired. In one example the prime mover might be part of a trenching machine or it might be a tractor or some other vehicle used to convey the backfill device. The backfill device itself may have an engine or drive to provide translational movement (as well as a drive or motor to drive rotation of the augers).

Preferably, the device comprises a drive to control the vertical angle of attack of the or each auger. Preferably, the drive is a hydraulic drive. Importantly, a drive such as a hydraulic arm or connector may be provided coupled to one or both of the augers to drive down the distal end of the auger with respect to the front end (the end closest to the frame). This, in effect, will alter the vertical angle of attack of the auger and can be used to force the auger to engage with more material and to thereby transfer more material to a trench per rotation of the axle or thread.

Preferably, a first of the augers is arranged to fill the trench and a second is arranged to move earth on top of the filled trench. The augers are in one example positioned such that as they move forward along the line of the longitudinal axis of the trench one is in front of the other. In this example a first of the augers (the front most auger) will serve to fill the trench and the second will serve to force material on top of the filled trench.

Preferably, the device comprises a cutting boom to dig a trench for filling by the first and second augers.

Preferably, the cutting boom is a rotating chain cutting boom.

Preferably, the augers are provided with hydraulic motors to drive rotation thereof.

Preferably, the device comprises one or more shock absorbers provided coupled to the augers. The shock absorbers provide the ability to absorb the effect of any unexpected obstacles that the device encounters on the seabed or earth as it operates. Preferably an independent shock absorber is provided on each of the augers so as to enable each of the augers independently to respond to obstacles or sudden changes it encounters. Preferably, each of the augers comprises a central axle and a thread formed thereon and in which at least sone of the first and second augers comprises a second thread out of phase and smaller in amplitude than the first thread.

Preferably, the second thread is out of phase to the extent that it is positioned at any point along the axis halfway between the adjacent fins of the first thread.

According to a second aspect of the present invention, there is provided a backfilling attachment, comprising: a frame for connection to a machine such as a trenching machine arranged to cut a trench in the ground; the backfilling attachment comprising: a first auger and a second auger arranged coupled to the trenching machine and driven so as to drive earth from the dug trench back into the trench to thereby backfill the trench. In one example the backfilling machine can be coupled to a trenching apparatus. In other examples it may be used for backfilling a trench that was formed with a separate trenching machine and so, for example could simply be connected to a prime mover without any trenching capacity.

According to a third aspect of the present invention, there is provided a method of backfilling a trench, the method comprising: providing a first auger and a second auger arranged coupled or couplable to a trenching machine and driving the augers so as to drive earth from a dug trench back into the trench to thereby backfill the trench.

Preferably, the method comprises arranging the first and second augers at acute angles relative to the longitudinal direction of the trench.

Preferably, the method comprises arranging the first and second augers to be overlapped such that in use the entire width of the trench is covered by one or both of the augers.

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which:

Figure 1 is a view of a backfill device seen from below; Figure 2 is a perspective view of a backfill device connected to a trenching device;

Figure 3 is a view from behind of the assembly of Figure 2;

Figure 3A is a schematic representation of a trench and backfill auger device;

Figures 4A and 4B are views of the backfill device of Figure 1 looking rearwards, showing alternative types of shock absorber;

Figure 5 is a schematic view of a second example of a backfill device connected to the prime mover of a trenching apparatus;

Figure 6A is a perspective view from above of the system of Figure 5;

Figures 6B to 6E are side views of the system of Figure 6A with cylinders in different states of operation; and.

Figure 7 is a view from below of the augers of the backfill assembly of Figures 5 and 6.

There is provided herewith a trenching and backfill device including, in embodiments, a trenching machine arranged to cut a trench in the ground and a backfill device coupled to the trenching machine. The backfill device includes a first and second auger arranged coupled to a trenching machine. In use, the first and second augers are driven as the trenching machine moves forward digging a trench. Thus, in operation, the trench is dug and subsequently filled in by the backfill device. Typically, between the two processes of digging and backfilling, some cable, pipe or conduit will be laid in the bottom of the trench. This can be done by apparatus connected to the same prime mover of the trenching and backfill device or alternatively independently thereof.

The trenching and backfill device described herein is suitable for applications both on land and subsea. Typically, in subsea trenching the spoil which comes out from the trench as it is excavated is dispersed over a large area, due to currents pushing it away from the trench to one or both sides of the trench. Depending on the depth and dimensions of the trench, it is typical that a layer of spoil is positioned anything from two to ten inches (5 to 25 centimetres) deep on either side of the trench and can extend up to six or seven metres to either side of the trench. The present device comprises a first and second auger arranged to be driven and in doing so to force the material that has been spread on either side of the trench back to within the trench.

Referring to Figure 1, the assembly 2 comprises a first auger 4 and a second auger 6. The augers are each provided with a central axle 8 coupled to a drive device 10 such as a hydraulic drive motor. In use, the hydraulic drive motors 10 are themselves connected to hydraulic lines (not shown in Figure 1) which are arranged to provide a hydraulic drive fluid to the motors 10 to cause rotation of the axles 8. In this example viewed form above the augers form the shape of a staggered chevron (also seen clearly in Figure 3A).

Given that the translational position of the augers 8 within the staggered chevron does not change as the device moves generally along the longitudinal axis of a trench, the engagement of the threads 12 drives material on either side of the trench towards the centre of the trench and thereby fills the trench.

In the examples shown, a second thread 14 is provided on each of the augers but this is an optional element and will be described in greater detail below.

The threads 12 of the augers include cutting elements 16 which, when driven by rotation of the augers can cut or otherwise engage with the surface upon which they are positioned. The surface can be both the seabed when used in a subsea location or simply the surface of the earth when used on land.

A frame 18 is provided which, in use, is typically fixedly connected to the prime mover of a trenching device. Thus, the trenching device, as it moves forward in a generally longitudinal direction cuts a trench which will then be filled by the operation of the augers 4 and 6. The frame includes various articulated members including support members 25 to which the first and second augers may be mounted or coupled. Looking at Figure 2, the prime mover 20 comprises caterpillar treads 22 and a cutting boom (not shown) arranged such that in use, as the device moves forwards (in the direction X as seen in figure 2) the spoil or earth arranged on either side of the trench will be driven in towards the trench. The trench is thus filled such that a single movement of the prime mover 20 serves to both dig the trench and to fill it in afterwards.

A frame 18 is provided which serves to couple the backfill device 2 to the chasse or housing 26 of the prime mover.

Each of the augers is provided with a housing 28 which is generally curved on its inner surface so as to provide a cover for the augers as they rotate. As seen in Figure 2, the housings 28 have a back wall 30 with an underlip 32 which forms a flat surface engaged with the earth or seabed 34 as it operates. This is typically roughly at the level of the seabed or earth before the trench was built such that the material forming the layer within which the augers are shown operating is formed of excavated material from the trench.

An opening 36 is provided in the back wall 30 of the housing which provides a route or passage through which, e.g. earth, soil or sand can be deposited within the trench 24.

Importantly for this preferred embodiment, the direction of rotation of the augers is clockwise as viewed from the distal end 37. This means that the cutting elements 16 are effectively forced to move in an upwards direction upon engagement with the earth or other formation. This provides a beneficial bias to the augers which will ensure that they remain in contact with the earth.

In the example of Figure 2 the backfill device is pulled behind a prime mover as it moves along a trench being backfilled. In another example the backfill device could instead be pushed from behind. In this case the housing of the augers would be shaped appropriately to expose the threads of the augers to the material that is being driven into the trench being filled. In another example a backfill device could be provided both at the front and rear of a prime mover so that one is pushed and one is pulled. Both or just one (or neither) could be engaged with the soil or earth at any point in time. This can be achieved for example by operation of cylinders (51 and 53 if provided) described below with reference to Figures 5 and 6A to 6E.

Figure 3 shows a view from behind of the trenching and backfill device. The trench 24 is clearly visible as are the first and second augers 4 and 6. As can be seen, the augers 4 and 6 are positioned with respect to the earth or spoil such that they are able to retrieve some of the material from the trench that might have dispersed and drive it towards the trench. In the example shown, the first auger 4 will be arranged to substantially fill the trench, whereas the second auger 6, which, in the direction of movement of the device, comes after the first auger 4, is arranged to put the spoil on top of the filled trench.

The angular configuration of the augers is such that they define an acute angle with respect to the longitudinal direction of the trench 24. Referring to Figure 3a, the angle 0 can be seen which represents the angle of the first and second augers 4 and 6, with respect to the longitudinal direction X of the trench 24. Preferably the angle is the same for both augers although in one embodiment the angles are not the same such that one auger is less angled with respect to the longitudinal axis of the trench than the other. Preferably each angle (whether the same or different for each auger) is between 20 and 70 degrees and more preferably between 30 and 60 degrees. Most preferably the angles for both augers are the same and are 45 degrees.

As can be seen, the dimensions of the augers are such that the entire width of the trench is covered by one or both of the augers. Typically, each auger may be between 2 and 5 metres long and preferably between 3 and 4 metres long.

The angular arrangement of the augers is beneficial since it ensures that the end bearing arrangement typically provided at the distal end (opposite from the drive end) of the augers are arranged such that the bearings run free of solid material in the area at the sides of the trench. As seen in Figure 3 the augers cut into the seabed or earth so as to define a side wall 39 that defines the limit of the material that has been driven towards the trench 24. The fact that the end faces of each of the augers and auger housings shown generally as 41 are perpendicular to the longitudinal axis of the augers means that they do not contact the side walls 39 directly. A space 38 is defined between them which means that the bearings of the augers are not in typically, or in normal operation, in contact with the earth or seabed material.

Figure 4A is a view from above of the backfill device in operation. As can be seen, the first auger 4 is driven via motor so as to drive material generally in the direction Y to fill the trench.

In the example shown in Figure 4A, a hydraulic shock absorbing mechanism 40 is provided which includes a cross beam 40 and a shock absorber 44. The shock absorber 44, which typically might simply be a spring, functions to absorb shocks that either of the augers may experience due, for example, to encountering a larger rock or item on the ground or seabed. The shock absorber is configured to be stiff but nonetheless to provide some absorption when required.

Figure 4B shows a second example of shock absorber arranged within the backfill device. In this example the shock absorber is formed of a single arm 42 including a shock absorbing 44. Again, any suitable for of shock absorber cold be used, such as a spring. The shock absorbers of both Figures 4A and 4B are advantageous in the situation in which, say, a large obstacle is buried in the surface and a small portion protruding. The shock absorber enables the auger on only one side to lift over the protruding obstacle.

Referring now to Figures 5 and 6A, a second embodiment of the trenching and backfill device is provided. Like components will not be described in detail since it is clear following the description of Figures 1 to 4, what their function is. However, the example of Figure 5 includes clearing teeth 48 which are arranged pointing forwards with respect to the leading surface 50 of the housing of the auger. The teeth 48 are connected to arms 52 which themselves are coupled to the auger housing. The teeth, in combination with the housing and augers themselves, are arranged to lift boulders or rocks or anything else they encounter which might cause an obstruction to the trenching and backfill device as it operates.

As can be seen two pairs 51 and 53 of hydraulic drives are provided. A first pair

51 are provided as tilt cylinders. These are operable to drive or tilt the augers 4 and 6 upwards and downwards with respect to the surface 46 of the seabed or earth upon which the operation is being conducted. The vertical angle of attack of the augers is thus varied by operation of the tilt cylinders 51. This enables the outside of the auger to be lowered deeper than the inside, i.e. closer to the trench so that more of the material that has been spread to the sides of the trench can be utilised to fill the trench. This is particularly advantageous in a subsea application in which the spread of earth or material from the trench may be significant..

The second pair of hydraulic drives 53 are referred to as lift cylinder as these are operable to lift the entire assembly of the augers and frame to which they are connected up, say 4 or 5 feet (roughly 1.2-1 ,5m), so that the augers are free of the earth or seabed. The prime mover or tractor to which the backfill device is coupled can then move to another trench for continued operation or possibly simply move away, say, for servicing. In the examples shown the tilt and lift cylinders 51 and 53 are included as pairs since this provides a balanced and effective operation. However, in some embodiments each pair may be replaced by a single cylinder or other such lift, or control or drive mechanism.

Figures 6B to 6E are side views of the system of Figure 6A with cylinders in different states of operation. Looking first at Figures 6B and 6C, a side view of the backfill device is shown with the lift cylinders contracted (Figure 6B) and extended (Figure 6C). The effect of extending the cylinders 53 is to lift the entire assembly whilst substantially maintaining the augers (only frame members 25 schematically shown) in a horizontal configuration, or at the very least maintaining the angular position with respect to ground and/or the prime mover or support frame.

Looking now at Figures 6D and 6E, a side view of the backfill device is shown with the tilt cylinders contracted (Figure 6E) and extended (Figure 6D). The effect of extending the cylinders 51 is to lift downwards the augers (only frame members 25 schematically shown). This will cause the distal ends of the augers to be deeper than the rest and therefore cause the augers to engage with more material on each rotation of the axes than they otherwise would. Furthermore, it is possible that a backfill device is provided in which only tilt or only lift cylinders or mechanisms are included.

Referring to Figure 7, what can be seen is importantly, that there are two threads provided on each of the augers. Referring to the first auger 4, a first thread 54 has a large amplitude whereas a second thread 56 has a smaller amplitude. Typically, the relative amplitude of the large 54 and small 56 threads might be 3:1 or 2:1. The pitch 58 is the same, which means that the first and second threads are able to run along the length of the axle 8 without interference. Importantly, the function of the second thread 56 is to drive rocks or stones which might be smaller than the pitch 58 of the larger thread 54 and stop them getting stuck in the housing of the auger. Specifically, the second thread 56 is arranged to drive out stones to stop them being trapped between the axle 8 and the housing 28 of the auger.

If a greater degree of protection is desired, more than one second thread 56 can be provided within the pitch 58 of the first thread 54.

A method is also provided of trenching and backfilling a trench. Preferably, in a subsea environment, a device is provided as described above including a cutter such as a chain cutting boom together with a backfill device such as that shown in any of Figures 1 to 7. The method comprises driving the cutting boom to cut a trench and subsequently driving the augers of the backfill device so as to fill the trench after something has been placed within it, such as a cable or conduit.

Embodiments of the present invention have been described with particular reference to the examples illustrated. However, it will be appreciated that variations and modifications may be made to the examples described within the scope of the present invention.