Page:Walker (1888) The Severn Tunnel.djvu/75

28 The shields were of oak, made to fit as nearly as possible to the interior of the shaft. One shield, when put together, was lowered to cover the entrance to the western heading; then the second in like manner lowered to cover the entrance to the eastern heading; and when lowered to their proper position, heavy struts, also of oak, were to be fixed between them and wedged up tight.

In addition to this the faces of the shields, where they were to come in contact with the brickwork, were padded with soft material soaked in tar.

The only difficulty about the operation was that the shields must be lowered by signals received from divers, who must be down the shaft at the level of the headings, and that the struts must be fixed and wedged up also by divers at the same level.

The depth of water from the shield to the surface being about 140 feet, the pressure upon the divers was so great that very few men were able to bear it at all, and no man could do work requiring great physical exertion under that pressure. In order to reduce the pressure to some extent Sir John Hawkshaw consented to my starting the pumps and lowering the water in the shaft 50 feet. The three pumps were accordingly started on the 6th January, and the lowering of the shields commenced immediately afterwards.

On the 10th January, No. 2 26-inch pump broke down; the top valve, not being properly secured and