EP2840187A1

EP2840187A1 - Method and apparatus for forming a trench in a sea floor

Info

Publication number: EP2840187A1
Application number: EP13181359.4A
Authority: EP
Inventors: Roger Paul White; Simon Vivian Ranulf Bateson; John Graeme Walker
Original assignee: Soil Machine Dynamics Ltd
Current assignee: Soil Machine Dynamics Ltd
Priority date: 2013-08-22
Filing date: 2013-08-22
Publication date: 2015-02-25

Abstract

A universal plough (2) apparatus for forming a trench in a sea floor is disclosed. The plough comprises a body (4) and a share (20) supported by the body for cutting a trench in the sea floor by means of towing of the plough. The share is adapted to cut a first trench portion having first side walls inclined relative to each other, and a share extension boot (38) is adapted to cut a second trench portion having generally parallel side walls in the first trench portion subsequently to cutting of the first trench portion.

Description

The present invention relates to a method and apparatus for forming a trench in a sea floor, and relates particularly, but not exclusively, to a method and apparatus for installing a cable in a trench in a sea floor.
It is known to install a cable in a trench in a sea floor by using a boulder clearing apparatus to clear debris such as boulders from the region where the trench is to be formed, and then to tow a trenching plough by a ship to form a trench having sidewalls inclined relative to each other. After the cable is laid in the trench, a backfill apparatus is used to push spoil displaced by formation of the trench into the trench to bury the cable.
This known arrangement suffers from the disadvantage that several separate apparatus are required which significantly increases costs, and in order to bury a cable to a depth of 2.5 metres, the known cable plough operates at a pulling force of 350 Tonnes and has a weight of 160 Tonnes.
Preferred embodiments of the present invention seek to overcome one or more of the above disadvantages of the prior art.
According to an aspect of the present invention, there is provided an apparatus for forming a trench in a sea floor, the apparatus comprising:-

a body; and
soil cutting means supported by the body and adapted to cut a trench in the sea floor by means of towing of the apparatus, wherein the soil cutting means comprises at least one first cutting part, adapted to cut a first trench portion in the sea floor, the first trench portion having first side walls inclined relative to each other at a first angle, and at least one second cutting part, adapted to cut a second trench portion in said first trench portion, subsequently to cutting of said first trench portion, wherein said second trench portion has second side walls inclined at a second angle, smaller than said first angle, relative to each other.

By providing at least one first cutting part, for cutting a first trench portion and at least one second cutting part for cutting a second trench portion in said first trench portion, subsequently to cutting of said first trench portion, this provides the advantage of enabling the cable to be buried to the required depth using a smaller pull force. For example, it has been found that a cable can be buried to a depth of 2.5 metres by means of an apparatus weighing 70 Tonnes and having a pull force of 150 tonnes, compared with a prior art cable plough having a weight of 160 Tonnes and operating at a pull force of 350 Tonnes.
The second side walls may be substantially parallel to each other.
At least one said second cutting part may be adapted to be mounted to at least one respective said first cutting part subsequently to cutting of said first trench portion.
This provides the advantage of enabling the apparatus to be easily converted from its first pass mode, in which the first trench portion is cut, to its second pass mode, in which the second trench portion is cut.
According to another aspect of the present invention, there is provided an apparatus for forming a trench in a sea floor, the apparatus comprising:-

a body;
soil cutting means supported by the body and adapted to cut a trench in the sea floor by means of towing of the apparatus in a cutting position of said soil cutting means and to be disengaged from the sea floor in a raised position of said soil cutting means;
first ground engaging means for supporting said body and located forwards of said soil cutting means in a direction of travel of the apparatus; and
first debris displacing means adapted to be located forwards of said first ground engaging means in the direction of travel of the apparatus and adapted to displace debris from a path of said soil cutting means.

By providing first debris displacing means adapted to be located forwards of the first ground engaging means in the direction of travel of the apparatus for displacing debris from a path of the soil cutting means, this provides the advantage of avoiding the need for a separate boulder clearing apparatus, as a result of which fewer pieces of apparatus are required, thereby reducing costs.
The first debris displacing means may be removably mounted to the apparatus.
The apparatus may further comprise second debris displacing means arranged rearwards of said soil cutting means in the direction of travel of the apparatus for displacing debris away from said apparatus.
The second debris displacing means may comprise at least one detachable extension for increasing the range of said second debris displacing means.
This provides the advantage of enabling conventional mouldboards, which may be used to displace spoil generated by formation of the trench in another mode of the apparatus, to form part of the second debris displacing means. This enables easy and rapid conversion of the apparatus from a debris clearing mode to a trench cutting mode, while minimising the number of components required.
The apparatus may further comprise second ground engaging means located rearwards of said second debris displacing means in a direction of travel of the apparatus.
The second debris displacing means may be adapted to displace debris away from a path of said second ground engaging means.
This provides the advantage of enabling the second ground engaging means to engage relatively stable ground after passage of said second debris displacing means.
The first debris displacing means may be adapted to displace debris when said soil cutting means is in a raised position thereof.
According to a further aspect of the present invention, there is provided an apparatus for forming and/or filling a trench in a sea floor, the apparatus comprising:-

a body;
soil cutting means adapted to be removably mounted to the apparatus and supported by the body, and adapted to cut a trench in the sea floor by means of towing of the apparatus in a first configuration thereof; and
soil displacing means adapted to be removably mounted to the apparatus and adapted to displace soil into the trench in a second configuration of the apparatus.

By providing removable soil cutting means for cutting a trench in a first configuration, and removable soil displacing means for displacing soil into the trench in a second configuration, this provides the advantage of enabling easy and rapid conversion of the apparatus from a trench cutting mode to a backfill mode, requiring fewer components and thereby reducing cost.
The soil displacing means may comprise at least one detachable extension for increasing the range of said soil debris displacing means.
This provides the advantage of enabling detachable extensions to be used in boulder clearing and backfill modes of an apparatus, thereby minimising the number of components required.
The body may comprise a first body member having attachment means for deploying said apparatus and/or control means for enabling control of operation of said apparatus, and a second body member removably attached to said first body member.
This provides the advantage of enabling permanently required features such as lift points, hydraulic power units and electronics to be located on the first body member, and features only required in certain modes of operation to be located on the second body portion, thereby minimising the number of components required and reducing costs.
The apparatus may further comprise at least one attachment member for applying a towing force to the apparatus at a plurality of locations on said attachment member, wherein said attachment member is adapted to be pivoted relative to the body.
This provides the advantage of enabling the effect of inclines in the sea floor to be corrected by steering of the apparatus.
According to a further aspect of the present invention, there is provided a method for forming a trench in a sea floor, the method comprising towing an apparatus as defined above such that said first cutting part cuts said first trench portion in the sea floor, and towing the apparatus subsequently to cutting of said first trench portion such that said second cutting part cuts said second trench portion.
The method may further comprise towing an apparatus as defined above to displace debris from a path of said soil cutting means prior to cutting of said first trench portion.
The method may further comprise towing an apparatus as defined above subsequently to formation of said trench to displace debris into said trench to cover an elongate object located in the trench.
The method may further comprise locating an elongate object in the trench.
A preferred embodiment of the invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings in which:-

Figure 1 is a plan view of a universal plough embodying the present invention in a boulder clearing mode thereof;
Figure 2 is a side view of the plough of Figure 1;
Figure 3 is a plan view of the plough of Figures 1 and 2 in a first pass trenching mode thereof;
Figure 4 is a side view of the plough of Figure 3;
Figure 5 is a plan view of the plough of Figures 3 and 4 in a second pass trenching mode thereof;
Figure 6 is a side view of the plough of Figure 5;
Figure 7 is a plan view of the plough of Figures 1 to 6 in a back fill mode thereof; and
Figure 8 is a side view of the plough of Figure 7.

Referring to Figures 1 and 2, a universal plough 2 for clearing debris such as boulders from a region of the sea bed where a trench is to be formed, forming the trench in the sea bed for receiving a cable (not shown) and filling the trench subsequently to insertion of the cable into the trench is shown. The plough 2 has a body 4 comprising a first body member 6 supporting a hydraulics unit 8 and an electronics pod 10 for controlling the hydraulics unit 8, and a second body member 12 removably mounted to the first body member 6. A single point lift attachment 14 is provided on the first body member 6.
First ground engaging means in the form of a pair of adjustable front skids 16 is mounted to the first body member 6 by means of hydraulic rams 18. The hydraulic rams 18 enable the height of the front skids 16 to be adjusted relative to the body 4, which in turn enables the height of soil cutting means in the form of a plough share 20 for cutting a trench in the sea floor to be adjusted relative to the sea floor. The share 20 is mounted to the second body member 12, as well as fixed mouldboards 22, the purpose of which will be described in greater detail below.
First debris displacing means in the form of a pair of boulder clearing blades 24 for displacing debris away from a path of the share 20 is removably mounted forwards of the adjustable front skids 16. A towing cable 26 is mounted to the ends of a pivotable bar 28 which is pivotably mounted to the first body member 6 and is pivotable relative to the first body member 6 by means of respective hydraulic rams (not shown) to enable steering of the plough 2. This enables the plough 2 to counteract the effect of inclines in the sea bed.
Second debris displacing means in the form of a pair of adjustable inner mouldboards 30 having detachable outer mouldboards 32 is pivotably mounted to the second body member 12. Second ground engaging means in the form of a pair of rear stabilisers 34 is mounted to the second body member 12 behind the inner mouldboards 30.
In a boulder clearing mode of the plough 2, prior to formation of a trench, the share 20 is raised clear of the sea bed by adjustment of the adjustable front skids 16 by hydraulic rams 8, and the plough 2 is towed by a vessel to the left as shown in Figures 1 and 2. The boulder clearing blades 24 clear a path for the front skids 16 and share 20, and the adjustable inner mouldboards 30 with detachable outer mouldboards 32 clear a path for the rear stabilisers 34.
Referring to Figures 3 and 4, in order to convert the plough 2 to its first pass trenching mode for forming a first trench portion of a trench in the sea bed, the front boulder clearing blades 24 and rear detachable outer mouldboards 32 are removed, and the adjustable inner mouldboards are pivoted outwards relative to the second body member 12 by means of respective hydraulic cylinders 36. The share 20 brought into its cutting position relative to the sea bed by raising the adjustable front skids 16, as shown in Figure 4. The plough 2 is then towed by the vessel such that the share 20 forms a shallow, truncated V-shaped trench, i.e. a generally flat bottomed trench of depth 1.2 m having inclined side walls. The fixed mouldboards 22 and adjustable inner mouldboards 30 displace spoil generated in forming the trench outwardly sideways of the trench to form spoil heaps on each side of the trench outwards of rear stabilisers 34. If inclines in the sea bed are encountered, the effect of such inclines can be corrected by adjusting the orientation of the pivotable member 28 relative to the first body member 6 by means of hydraulic rams.
Referring now to Figures 5 and 6, the plough 2 is converted to its second pass trenching mode by mounting a removable share extension boot 38 to the lower part of the share 20. The vessel tows the plough to cause the share extension boot 38 to cut a second trench portion having generally parallel side walls at the bottom of the first trench portion. The total depth of the bottom of the second trench portion below the sea bed is typically 2.2 m to 3.2 m. Spoil generated in formation of the second trench portion is partially displaced from the trench by means of the fixed mouldboards 22 and adjustable inner mouldboards 30, but some spoil will remain in the trench and can be subsequently displaced by means of a jetting apparatus (not shown) which will be familiar to persons skilled in the art. Subsequently to removal of the remaining spoil at the bottom of the second trench portion by means of the jetting apparatus, the cable (not shown) is laid into the second trench portion.
Referring now to Figures 7 and 8, in order to convert the plough 2 to its backfill mode, the second body member 12 is detached from the first body member 6 and replaced by a third body member 40. Soil displacing means in the form of a pair of mouldboards 42 is pivotably mounted to the third body member 40, and detachable outer mouldboards 44 are mounted to the mouldboards 42. Mouldboard retaining chains 46 limit the extent to which the mouldboards 42 can pivot outwards of the body 4. A pair of adjustable rear skids 48 are mounted to the third body member 40 and the height of the skids 48 can be adjusted by means of hydraulic rams 50. The plough 2 is then towed by the vessel such that the mouldboards 42, 44 direct spoil generated during formation of the trench back into the trench to cover the cable located in the second trench portion. The adjustable rear skids 48 are located rearwardly of the mouldboards 42, 44, so that the plough 2 is supported on a relatively flat surface after spoil heaps have been displaced by the mouldboards 42, 44.
It will be appreciated by persons skilled in the art that the above embodiment has been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.

Claims

An apparatus for forming a trench in a sea floor, the apparatus comprising:-
a body; and

soil cutting means supported by the body and adapted to cut a trench in the sea floor by means of towing of the apparatus, wherein the soil cutting means comprises at least one first cutting part, adapted to cut a first trench portion in the sea floor, the first trench portion having first side walls inclined relative to each other at a first angle, and at least one second cutting part, adapted to cut a second trench portion in said first trench portion, subsequently to cutting of said first trench portion, wherein said second trench portion has second side walls inclined at a second angle, smaller than said first angle, relative to each other.
An apparatus according to claim 1, wherein the second side walls are substantially parallel to each other.
An apparatus according to claim 1 or 2, wherein at least one said second cutting part is adapted to be mounted to at least one respective said first cutting part subsequently to cutting of said first trench portion.
An apparatus for forming a trench in a sea floor, the apparatus comprising:-
a body;

soil cutting means supported by the body and adapted to cut a trench in the sea floor by means of towing of the apparatus in a cutting position of said soil cutting means and to be disengaged from the sea floor in a raised position of said soil cutting means;

first ground engaging means for supporting said body and located forwards of said soil cutting means in a direction of travel of the apparatus; and

first debris displacing means adapted to be located forwards of said first ground engaging means in the direction of travel of the apparatus and adapted to displace debris from a path of said soil cutting means.
An apparatus according to claim 4, wherein the first debris displacing means is removably mounted to the apparatus.
An apparatus according to claim 4 or 5, further comprising second debris displacing means arranged rearwards of said soil cutting means in the direction of travel of the apparatus for displacing debris away from said apparatus.
An apparatus according to claim 6, wherein the second debris displacing means comprises at least one detachable extension for increasing the range of said second debris displacing means.
An apparatus according to claim 6 or 7, further comprising second ground engaging means located rearwards of said second debris displacing means in a direction of travel of the apparatus.
An apparatus according to claim 8, wherein the second debris displacing means is adapted to displace debris away from a path of said second ground engaging means.
An apparatus according to any one of claims 4 to 9, wherein the first debris displacing means is adapted to displace debris when said soil cutting means is in a raised position thereof.
An apparatus for forming and/or filling a trench in a sea floor, the apparatus comprising:-
a body;

soil cutting means adapted to be removably mounted to the apparatus and supported by the body, and adapted to cut a trench in the sea floor by means of towing of the apparatus in a first configuration thereof; and

soil displacing means adapted to be removably mounted to the apparatus and adapted to displace soil into the trench in a second configuration of the apparatus.
An apparatus according to claim 11, wherein the soil displacing means comprises at least one detachable extension for increasing the range of said soil debris displacing means.
An apparatus according to any one of the preceding claims, wherein the body comprises a first body member having attachment means for deploying said apparatus and/or control means for enabling control of operation of said apparatus, and a second body member removably attached to said first body member.
An apparatus according to any one of the preceding claims, further comprising at least one attachment member for applying a towing force to the apparatus at a plurality of locations on said attachment member, wherein said attachment member is adapted to be pivoted relative to the body.
A method for forming a trench in a sea floor, the method comprising towing an apparatus according to any one of claims 1 to 3 such that said first cutting part cuts said first trench portion in the sea floor, and towing the apparatus subsequently to cutting of said first trench portion such that said second cutting part cuts said second trench portion.
A method according to claim 15, further comprising towing an apparatus according to any one of claims 4 to 10 to displace debris from a path of said soil cutting means prior to cutting of said first trench portion.
A method according to claim 15 or 16, further comprising towing an apparatus according to any one of claims 11 to 14 subsequently to formation of said trench to displace debris into said trench to cover an elongate object located in the trench.