Abstract
IN the course of developing underground cable networks, the engineer has sometimes to negotiate waterways and harbours. For large waterways three methods are used. The first is to make a special cable tunnel. But the expense of construction is heavy, and is only justified when a large block of main cables has to be taken across. Examples of this type are the crossings under the Thames at Barking, Deptford and Battersea and underneath the Tyne at Newcastle. The second method is to dredge a trench in the river bed in which the cables are laid directly, and the third method is to lay them in the bed of the waterway without recourse to dredging. The second method is, when practicable, preferable to the third method, especially in navigable waterways, where the ships' anchors damage them. In certain cases, owing to the width of the waterway or because the nature of its bed renders dredging impracticable, the third method is employed. In the Engineering Supplement to the Siemens Magazine of March, it is pointed out that when this is done in running or tidal waters, a new problem arises. No matter how carefully the cable is laid, it may at any time, due to the shifting of the bottom, be left suspended between two points. In this condition, it is subject to high-frequency vibrations set up by the current. These vibrations are very harmful to the lead as they rapidly produce inter-crystalline fracture and failure due to ingress of water. Messrs. Siemens have successfully combated this trouble by a special type of cable. A rubber hose protection is applied between the lead sheathing and the armouring. This damps out harmful frequency vibrations before they reach the lead.
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Underwater Power and Telephone Cables. Nature 139, 621 (1937). https://doi.org/10.1038/139621c0
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DOI: https://doi.org/10.1038/139621c0