GB2134567A

GB2134567A - Trenching plough

Info

Publication number: GB2134567A
Application number: GB08402585A
Authority: GB
Inventors: Alan Richard Reece
Original assignee: BP PLC
Current assignee: BP PLC
Priority date: 1983-02-05
Filing date: 1984-02-01
Publication date: 1984-08-15
Also published as: GB8402585D0; GB2134567B

Abstract

A trenching plough for cutting a trench for a pipeline or cable in the sea bed has a shield (2) trailing behind it to support the walls of the trench. This prevents the walls caving in before the pipeline or cable settles down in the bottom of the trench. The shield is preferably constructed from inflatable flexible tubes. <IMAGE>

Description

SPECIFICATION Trenching plough This invention relates to a towable trenching plough and more particularly to a trenching plough suitable for burying a pipeline or cable at an underwater site.

Pipelines and cables have previously been buried under the sea bed by means of trenching devices which are towed, usually by a surface vessel. Two type of trenching device have been used: one employs jets of water to make a trench into which the pipeline or cable settles, the other employs a share to cut the trench and is hereafter referred to as a trenching plough.

Trenching ploughs usually have some part which passes under the pipeline or cable and consequently the latter is often lifted a small distance from the sea bed before it is guided into the trench. The portion of the pipeline or cable thus lifted into a gently curving configuration clear of the sea bed is referred to as a span. Under certain conditions, the walls of the trench tend to collapse before the end of the span contacts the bottom of the trench, with the result that the burial may not always be to the required depth.

It is an object of the present invention to provide equipment to counteract this tendency.

Thus, according to the present invention there is provided a trenching plough for cutting a trench for a pipeline or cable in the sea bed having a shield trailing behind it to support the walls of the trench where the pipeline or cable spans.

The shield can be made of flexible material attached to the rear portion of the trenching plough to occupy the trench where the pipeline or cable spans.

The shield can be made of a plurality of tubes, conveniently inflatable by water and arranged to lie lengthwise in the trench.

In the deflated state the shield is preferably foldable and/or telescopic and can conveniently be extended by introducing water to effect inflation.

Preferably a number of tubes are provided, some of which are disposed above others and preferably some of the upper tubes are of relatively small diameter in relation to the lower tubes. The upper tubes may be spaced apart to provide space for the passage of the cable or pipeline. The general construction of the plough to which the shield is attached may be as described in our copending European Patent Application No. 0010915.

The invention is illustrated with reference to the accompanying drawings in which Figure 1 is a sectional view of a trench containing a shield attached to a trenching plough (not shown) and Figure 2 is a similar view of the trench with a shield of modified construction.

Referring to Figure 1 the shield indicated generally by numeral 2 is shown located in a trench 4 of generally trapezoidal shape. The shield 4 comprises six inflated rubber tubes 6 each about 30 m long. The tubes 6 are foldable when deflated and can be extended and inflated by pumping in water.

In Figure 2 the shield 3 comprises four tubes of the same type as in Figure 1 but includes four further, smaller tubes 8 whose diameter is about half the diameter of the larger tubes 7.

The pipeline 10 being trenched passes between the tubes 8 and over the tubes 7.

1. A trenching plough for cutting a trench for a pipeline or cable in the sea bed having a shield trailing behind it to support the walls of the trench where the pipeline or cable spans.

2. A trenching plough according to claim 1 wherein the shield is flexible.

3. A trenching plough according to claim 2 wherein the shield comprises a plurality of inflatable tubes.

4. A trenching plough according to claim 3 wherein the tubes are substantially parallel and in layers.

5. A trenching plough according to claim 4 wherein the tubes in the upper layer(s) are of smaller diameter than those in the lower layer(s).

6. A trenching plough according to any of claims 3-5 wherein the tubes are inflatable by water.

7. A trenching plough as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Trenching plough This invention relates to a towable trenching plough and more particularly to a trenching plough suitable for burying a pipeline or cable at an underwater site. Pipelines and cables have previously been buried under the sea bed by means of trenching devices which are towed, usually by a surface vessel. Two type of trenching device have been used: one employs jets of water to make a trench into which the pipeline or cable settles, the other employs a share to cut the trench and is hereafter referred to as a trenching plough. Trenching ploughs usually have some part which passes under the pipeline or cable and consequently the latter is often lifted a small distance from the sea bed before it is guided into the trench. The portion of the pipeline or cable thus lifted into a gently curving configuration clear of the sea bed is referred to as a span. Under certain conditions, the walls of the trench tend to collapse before the end of the span contacts the bottom of the trench, with the result that the burial may not always be to the required depth. It is an object of the present invention to provide equipment to counteract this tendency. Thus, according to the present invention there is provided a trenching plough for cutting a trench for a pipeline or cable in the sea bed having a shield trailing behind it to support the walls of the trench where the pipeline or cable spans. The shield can be made of flexible material attached to the rear portion of the trenching plough to occupy the trench where the pipeline or cable spans. The shield can be made of a plurality of tubes, conveniently inflatable by water and arranged to lie lengthwise in the trench. In the deflated state the shield is preferably foldable and/or telescopic and can conveniently be extended by introducing water to effect inflation. Preferably a number of tubes are provided, some of which are disposed above others and preferably some of the upper tubes are of relatively small diameter in relation to the lower tubes. The upper tubes may be spaced apart to provide space for the passage of the cable or pipeline. The general construction of the plough to which the shield is attached may be as described in our copending European Patent Application No. 0010915. The invention is illustrated with reference to the accompanying drawings in which Figure 1 is a sectional view of a trench containing a shield attached to a trenching plough (not shown) and Figure 2 is a similar view of the trench with a shield of modified construction. Referring to Figure 1 the shield indicated generally by numeral 2 is shown located in a trench 4 of generally trapezoidal shape. The shield 4 comprises six inflated rubber tubes 6 each about 30 m long. The tubes 6 are foldable when deflated and can be extended and inflated by pumping in water. In Figure 2 the shield 3 comprises four tubes of the same type as in Figure 1 but includes four further, smaller tubes 8 whose diameter is about half the diameter of the larger tubes 7. The pipeline 10 being trenched passes between the tubes 8 and over the tubes 7. CLAIMS

2. A trenching plough according to claim 1 wherein the shield is flexible.