EP0010915B1

EP0010915B1 - Trenching plough

Info

Publication number: EP0010915B1
Application number: EP79302297A
Authority: EP
Inventors: Alan Richard Reece
Original assignee: BP PLC
Current assignee: BP PLC
Priority date: 1978-10-26
Filing date: 1979-10-22
Publication date: 1982-10-27
Also published as: MX149074A; EP0010915A1; NO150322C; NO793429L; AU5208579A; DE2963948D1; NO150322B; AU534656B2; CA1123215A

Description

This invention relates to a trenching plough which is suitable for towing underwater to form a trench for a previously laid underwater cable or pipeline.
There have been previous proposals relating to ploughs for use on land, for example GB-A-1,349,515 describes a plough towed by a vehicle wherein the plough follows a path either directly behind, or parallel to, the towing vehicle. The line of travel of the plough is determined by that of the towing vehicle and a ram which adjusts the angle of a hinge connecting a towing beam of the vehicle to the plough.
Trenching ploughs have also been previously described for burying pipelines on the sea bed. Usually the plough is towed by means of a cable connected to a surface vessel. For example GB-A-1,384,078 describes a trenching plough which comprises a framework that straddles the pipeline to be buried and is pulled by means of a cable from a surface vessel. Even with careful control of the direction of the vessel, the line of the towing force may sometimes deviate significantly from the axis of the pipeline with the result that a potentially damaging lateral force is exerted on the pipeline.
It is an object of the present invention to reduce this problem by providing a plough in which the lateral component of the towing force (when the towing force is inclined to the axis of the pipeline or cable) acting on the pipeline or cable is reduced.
This is achieved by the combination of (i) having means for engaging the cable or pipeline located forward with respect to a landside and (ii) the hitch point through which the towing member e.g. cable is connected to the plough located so that the line of the towing force (projected if necessary) passes through a point over the landside. The towing member is connected to the plough at the hitch point allowing pivotal movement whereby the direction of travel of the plough is within limits independent of the direction of travel of the towing vehicle.
Thus according to the present invention a trenching plough (1) which is suitable for towing underwater to form a trench for a previously laid underwater cable or pipeline (8) comprises: a body (4) having attached thereto a soil cutting member (6), which soil cutting member in use forms a soil surface in the direction of travel of the plough (1), a landside (5) which engages the soil surface, a towing member (2) connected to a hitch point (3) in a manner that allows the direction of travel of the plough (1) to be inclined to the line of the towing force, the hitch point (3) being located so that in use the line of the towing force passed through a point above the landside (5) characterised in that the plough (1) is provided with steering means comprising an apparatus (9) for engaging the previously laid pipeline (8) or cable, and the towing member (2) is pivotally connected to the hitch point (3) whereby the direction of travel of the plough is, within limits, independent of the direction of travel of the towing vehicle, the steering means (9) being spaced apart from, and forward with respect to the landside (5), so that when the direction of travel of the plough is inclined to the line of the towing force the sideways forces on the pipeline (8) or cable are reduced.
Preferably the trenching plough (1) is further characterised in that the apparatus (9) for engaging the previously laid cable or pipeline is located at the front of the plough (1).
In one embodiment of the invention as shown by way of example in Fig. 6 the hitch point (46) can be located so that in use the projected line of the towing force (56) passes through the point (50) over the landside (45).
In most cases the point in the region of the landside will be located at a position along the length of the implement where the landside extends and rearward of the soil cutting member.
The hitch point can be movable on a laterally extending arm, the arm being so disposed so that the point moves on the circumference of a circle whose centre is at the point in the region of the landside.
The point in the region of the landside through which the line of the towing force passes can be located so that the components of the towing force and the soil cutting force in the direction of travel create no significant couple in the horizontal plane through that point.
The plough can be used for making a trench for a pipeline at an underwater site and can have in the region of the front thereof a carriage adapted to run on the pipeline so that at least a portion of the weight of the plough is supported by the pipeline.
The plough can further have located forward with respect to the carriage, a support member capable of contacting the ground to reduce the risk of overloading an unsupported section of pipeline.
The support member can be movable between a ground contacting position and a raised position free of the ground and means can be provided for moving the support member from one position to the other.
References to "above", "forward", "sideways" and "rear" refer to the implement in its disposition for normal use.
The term pipeline is intended to include flowlines. Although the trenching device according to the invention is intended primarily for use underwater it can nevertheless be used on land.
Reference to the line of towing force means the line of the towing force projected in the horizontal plane through the hitch point.
The trenching plough according to the present invention may be employed to make a trench parallel and close to a pipeline or cable which can be moved sideways into the trench at a later time. Alternatively, the plough can be employed to make the trench and place the pipeline or cable therein in one operation.
The plough is particularly suitable for use where the pipeline or cable has been previously installed on the sea bed although it is possible to use the plough to bury a pipeline or cable as it is laid down from a surface vessel.
The invention is illustrated by reference to the accompanying drawings in which:

Figure 1 is a side elevation of a soil moving implement in the form of a trenching plough showing the location of the hitch point, and
Figure 2 is a plan view of the trenching plough shown in Figure 1.
Figure 3 is a side elevation of the alternative embodiment of the trenching plough in which steering is effected by means of a sensor which follows the pipeline and controls a servo mechanism and hydraulic ram.
Figure 4 is a plan view of the embodiment in Figure 3.
Figure 5 is a side elevation of a further embodiment of the trenching plough in which the hitch point is located on a laterally extending arm, and
Figure 6 is a plan view of the trenching plough shown in Figure 5.

Referring to Figures 1 and 2 the trenching plough indicated generally by numeral 1 comprises a body in the form of beam 4 attached to the rear of which is a blade indicated generally by numeral 7, the leading face 6 of which is the soil cutting member and the sides 5 of which provide the landside. Located above the sides 5 is a hitch point in the form of a towing eye 3 to which a towing cable 2 is connected. The forward part of the beam 4 is attached to a laterally extending cross member 13 one end of which is attached to and supported by skid 10 on the sea bed 11. The trenching plough has a steering means in the form of guide wheels 9 which straddle pipeline 8 and are attached to the other end of cross member 13 remote from skid 10. By means of the guide wheels 9 the trenching plough follows the pipeline 8 thus requiring no additional steering. The effect of the hitch point 3 located over the landside 5 is that the sideways component of the towing force is resisted with the result that the steering effect of the towing force is significantly reduced. In the disposition shown in Figures 1 and 2 the plough cuts a trench parallel to the pipeline 8 which has been previously installed in its trench. At the rear of the plough is a scraper 12 to displace spoil to cover the pipeline.
Referring to Figures 3 and 4 the trenching plough indicated by reference numeral 21 is generally of similar construction to that shown in Figures 1 and 2 with the exception of the steering means. The plough comprises a body in the form of a beam 24 attached to the rear of which is a blade indicated generally by numeral 27 the leading face 26 of which is the soil cutting member and the sides 25 of which provide the landside. Located above the sides 25 is a hitch point in the form of towing eye 23 to which a towing cable 22 is attached. The forward part of the beam 24 is attached to a laterally extending cross member 28 the ends of which are attached to, and supported by, skids 30 and 31 on the sea bed. The plough has steering means in the form of sensor 32 which scans the pipeline 29 and controls a servo mechanism (not shown) which operates a hydraulic ram 33 which moves the skids 30 and 31 which have soil engaging blades (only one of which 34 is shown). By means of this arrangement the trenching plough is able to follow the pipeline 29 which may in places be buried as shown in Figure 3 and produce a trench parallel to the axis of the pipeline. Attached to the rear of the body 24 are a pair of scraper arms 35 to move the spoil.
Referring to Figures 5 and 6 the trenching plough indicated generally by numeral 41 comprises a body in the form of beam 44 attached to the rear of which is a blade indicated generally by numeral 47, the leading face of which is the soil cutting edge and the sides 45 of which provide the landside. In these respects the trenching plough is similar to the two embodiments previously described. The forward part of the beam 44 is attached to a laterally extending arm 43 the end of which is supported by skid 55. On the arm 43 is mounted a hitch point in the form of towing eye 46 which is movable on the arm 43 by means of roller 48. The arm 43 has a curved face 49 on which the roller 48 moves so that the hitch point 46 moves on the circumference of a circle whose centre is at point 50 which is over the landside 45. The effect of this is that the projected line of action of the towing force passes through point 50 with the result that the sideways component of the towing force is resisted by the landside 45.
The trenching plough has a steering means in the form of a pair of guide wheels 52 straddling the pipeline 54 the latter resting on a roller between the guide wheels 52. At the rear of the body is a pair of scrapers 60 for displacing soil sideways.
In use the trenching plough is towed by means of a line 56 attached to hitch point 46. The trenching plough passes along and under the pipeline 54. A trench is made into which the pipeline settles.
In the three embodiments shown the point through which the towing force passes, i.e. points 3, 23 and 50 are vertically above the effective centre of the landside in each case.
The present invention provides improved control of the trenching or other soil moving operation when the line of action of the towing force is up to 45° from the line of travel of the implement and particularly in the range up to 30°. Further the line of the towing force (when projected in the horizontal plane through the hitch point) passes through, or close to, a point on the vertical axis passing through the point of intersection of the lines of action of the soil forces on the cutting member and landside. Thus, any sideways force applied by the towing means is resisted by the landside to reduce the resultant couple in the horizontal plane. It is thus possible to steer the implement with a smaller steering force, with reduced risk of damage to the pipeline.
The embodiment in Figures 5 and 6 is particularly suitable for towing by an underwater tractor or other similar vehicle which cannot conveniently straddle the pipeline with the result that the towing force is always at an angle to the axis of the pipeline.

Claims

1. A trenching plough (1) which is suitable for towing underwater to form a trench for a previously laid underwater cable or pipeline (8) which trenching plough comprises: a body (4) having attached thereto a soil cutting member (6), which soil cutting member in use forms a soil surface in the direction of travel of the plough (1), a landside (5) which engages the soil surface, a towing member (2) connected to a hitch point (3) in a manner that allows the direction of travel of the plough (1) to be inclined to the line of the towing force, the hitch point (3) being located so that in use the line of the towing force passed through a point above the landside (5) characterised in that the plough (1) is provided with steering means comprising an apparatus (9) for engaging the previously laid pipeline (8) or cable, and the towing member (2) is pivotally connected to the hitch point (3) whereby the direction of travel of the plough is, within limits, independent of the direction of travel of the towing vehicle, the steering means (9) being spaced apart from, and forward with respect to the landside (5), so that when the direction of travel of the plough is inclined to the line of the towing force the sideways forces on the pipeline (8) or cable are reduced.

2. A trenching plough as claimed in claim 1 characterised in that the apparatus (9) is located at the front of the plough (1 ).

3. A trenching plough is claimed in claim 1 characterised in that the hitch point (46) is located so that in use the projected line of the towing force passes through a point (50) over the landside (45).

4. A trenching plough as claimed in claim 3 characterised in that the hitch point (46) is movable on a laterally extending arm (43) the arm (43) being disposed so that the hitch point (46) moves on the circumference of a circle whose centre is at the point (50) over the landside (45).