GB2104130A

GB2104130A - Laying cables under water

Info

Publication number: GB2104130A
Application number: GB08222267A
Authority: GB
Inventors: Norman Howard Waterhouse
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1981-08-03
Filing date: 1982-08-02
Publication date: 1983-03-02

Abstract

A method of cutting a trench in the sea bed comprises using a trench cutting device having high pressure water jets to cut the outline of the side and base of the trench, and low pressure water jets to lift the body of cut material out of the trench.

Description

SPECIFICATION Laying cables under water This invention relates to a method of, and apparatus for, laying cables, pipes or other elongate flexible members (hereinafter for convenience referred to as "cables") under water.

In the complete specification of our UK Patent No. 1466570 (our earlier patent) we have described and claimed a method of laying a cable below the bed of a body of water comprising forming a trench in the bed and laying in it a line (for example a steel hawser) having a greater strength and/or a lower cost than the cable; and then a separate second operation laying the cable from a cable-laying vessel in substantially the same trench by a submerged device caused to follow the path of the line.

As described in our earlier patent, the submerged device (such as a "plough") may be towed by the cable-laying vessel through a recovered length of the line layed in the first operation or otherwise, or it may have internal traction means.

In the specification of our published UK Patent Application No. 201 911 3A (our earlier patent application), we have described and claimed a method of laying one or more cables under water in substantially the same trench as a line already laid below the bed of the body of water comprising advancing a submerged cablepositioning device along the path of the line in a laying direction by traction means on said device pulling on the line ahead, and feeding the cable from a cable-laying vessel to said device in such a manner that any auxiliary lines extending between the vessel and the device are, relative to the laying direction, above and behind the flexible member.

We have also described and claimed in our earlier patent application apparatus for laying a cable under water in substantially the same trench as a line laid below the sea bed comprising a submersible trench clearing and cablepositioning device having traction means to pull on the line ahead to advance said device along the path of the line.

Cutting the initial trench to lay the line, or reexcavating the trench to lay the cable or cables, in granular material is usually effected by using a trench cutting device having low pressure water jets which supply a stream of water moving in a forward and upward direction at a speed in excess of the settling velocity of the granular particles.

This method, however, cannot be used when the material is cohesive.

According to the present invention, a method of cutting a trench in the sea bed comprises using a trench cutting device having high pressure water jets to cut the outline of the side and base of the trench, and low pressure water jets to lift the body of cut material out of the trench.

When a large or deep trench is required additional high pressure water jets may also be used to cut the body into smaller pieces to assist its removal.

This method can be used to cut the initial trench, or to re-excavate a previously cut trench and is suitable for use in cutting through granular or cohesive material.

This invention also includes apparatus for carrying out the method as hereinbefore described.

This invention is applicable to any of the apparatuses described in our earlier patent and our earlier patent application.

Preferably the device also comprises a separate hollow flexible guide as described and claimed in our European Patent Application No.

.................. filed the same day as this application, and claiming priorty from our UK Patent Application No. 8123677 filed 3 August, 1981.

The device preferably also comprises cutting and lifting means as described and claimed in our UK Patent Application No .................. filed the same day as this application, and claiming priority from our UK Patent Application No.

8123678 filed 3 August, 1981.

The device preferably also includes a plenum chamber surrounding each jet nozzle so that abrasive material (e.g. pea shingle or granite chippings) can be fed into the chamber, entrained in each jet, and then projected at the faying face at high velocity such that the faying face is broken up. This arrangement has particular use in excavating or re-excavating a trench in cohesive or hard material. By utilising concentric nozzles the abrasive material can be introduced into the centre of the jet stream, thereby avoiding abrasion of the bore of each nozzle.

Where the apparatus is used to re-excavate a trench, preferably the device also includes trench filling means comprising a suction system for collecting a proportion of material removed from the trench, a grading system to grade the collected material into various sizes, and a discharge system for initially covering the cable or cables in the trench with material of a suitable size to provide backfill to protect the cable or cables. The grading system preferably comprises a number of screens.

Claims

1. A method of cutting a trench in the sea bed comprises using a trench cutting device having high pressure water jets to cut the outline of the, side and base of the trench, and low pressure water jets to lift the body of cut material out of the trench.

2. A method as claimed in Claim 1, in which additional high pressure water jets are used to cut the body of cut material into smaller pieces to assist its removal.

3. Apparatus for carrying out the method as claimed in Claim 1 or Claim 2, comprising a trench cutting device having high pressure water jets to cut the outline of the side and base of the trench, and low pressure jets to lift the body of the cut material out of the trench.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Laying cables under water This invention relates to a method of, and apparatus for, laying cables, pipes or other elongate flexible members (hereinafter for convenience referred to as "cables") under water. In the complete specification of our UK Patent No. 1466570 (our earlier patent) we have described and claimed a method of laying a cable below the bed of a body of water comprising forming a trench in the bed and laying in it a line (for example a steel hawser) having a greater strength and/or a lower cost than the cable; and then a separate second operation laying the cable from a cable-laying vessel in substantially the same trench by a submerged device caused to follow the path of the line. As described in our earlier patent, the submerged device (such as a "plough") may be towed by the cable-laying vessel through a recovered length of the line layed in the first operation or otherwise, or it may have internal traction means. In the specification of our published UK Patent Application No. 201 911 3A (our earlier patent application), we have described and claimed a method of laying one or more cables under water in substantially the same trench as a line already laid below the bed of the body of water comprising advancing a submerged cablepositioning device along the path of the line in a laying direction by traction means on said device pulling on the line ahead, and feeding the cable from a cable-laying vessel to said device in such a manner that any auxiliary lines extending between the vessel and the device are, relative to the laying direction, above and behind the flexible member. We have also described and claimed in our earlier patent application apparatus for laying a cable under water in substantially the same trench as a line laid below the sea bed comprising a submersible trench clearing and cablepositioning device having traction means to pull on the line ahead to advance said device along the path of the line. Cutting the initial trench to lay the line, or reexcavating the trench to lay the cable or cables, in granular material is usually effected by using a trench cutting device having low pressure water jets which supply a stream of water moving in a forward and upward direction at a speed in excess of the settling velocity of the granular particles. This method, however, cannot be used when the material is cohesive. According to the present invention, a method of cutting a trench in the sea bed comprises using a trench cutting device having high pressure water jets to cut the outline of the side and base of the trench, and low pressure water jets to lift the body of cut material out of the trench. When a large or deep trench is required additional high pressure water jets may also be used to cut the body into smaller pieces to assist its removal. This method can be used to cut the initial trench, or to re-excavate a previously cut trench and is suitable for use in cutting through granular or cohesive material. This invention also includes apparatus for carrying out the method as hereinbefore described. This invention is applicable to any of the apparatuses described in our earlier patent and our earlier patent application. Preferably the device also comprises a separate hollow flexible guide as described and claimed in our European Patent Application No. .................. filed the same day as this application, and claiming priorty from our UK Patent Application No. 8123677 filed 3 August, 1981. The device preferably also comprises cutting and lifting means as described and claimed in our UK Patent Application No .................. filed the same day as this application, and claiming priority from our UK Patent Application No. 8123678 filed 3 August, 1981. The device preferably also includes a plenum chamber surrounding each jet nozzle so that abrasive material (e.g. pea shingle or granite chippings) can be fed into the chamber, entrained in each jet, and then projected at the faying face at high velocity such that the faying face is broken up. This arrangement has particular use in excavating or re-excavating a trench in cohesive or hard material. By utilising concentric nozzles the abrasive material can be introduced into the centre of the jet stream, thereby avoiding abrasion of the bore of each nozzle. Where the apparatus is used to re-excavate a trench, preferably the device also includes trench filling means comprising a suction system for collecting a proportion of material removed from the trench, a grading system to grade the collected material into various sizes, and a discharge system for initially covering the cable or cables in the trench with material of a suitable size to provide backfill to protect the cable or cables. The grading system preferably comprises a number of screens. Claims

4. Apparatus as claimed in Claim 3, in which the device also comprises a plenum chamber surrounding each jet nozzle so that abrasive material can be fed into the chamber, entrained in each jet, and then projected at the faying face at high velocity.

5. Apparatus as claimed in Claim 3 or Claim 4, in which the device also comprises trench filling means comprising a suction system for collecting a proportion of material removed from the trench, a grading system to grade the collected material into various sizes, and a discharge system for initially covering the cable or cables in the trench with material of a suitable size to provide backfill to protect the cable or cables.

6. Apparatus as claimed in Claim 5, in which the grading system comprises a number of screens.