Page:Walker (1888) The Severn Tunnel.djvu/81

32 We then got an extra valve made to drop down inside the rising-main of the pump. It was attached to wooden pump-rods 6 inches square. When lowered nearly to the top of the original valve, it was held down in position by the rods, and the pump started on the 31st. We found that it did fair duty, but after working four days it was evident that the shield would not hold back the water sufficiently to allow the pumps we then had to deal with it, and the attempt to pump out the shaft was abandoned till the new 75-inch engine with the 38-inch bucket-pump was ready for work.

In the meantime Sir John Hawkshaw had decided in January to lower the gradient of the tunnel at the ‘Shoots’ 15 feet, and to keep the gradient eastwards towards Bristol parallel to the old gradient at a depth of 15 feet below it, by this means preserving the gradient of 1 in 100 against the load. From the ‘Shoots’ westward the gradient was altered to 1 in 90, so that the lowering at the Old Pit at Sudbrook was 12 feet 7 inches; at the Marsh Pit, 7 feet 9 inches; and at the Hill Pit, 4 feet 9 inches; and the gradient ran out into the old levels in the open cutting on the Monmouthshire side.

Having decided to lower the gradient, and feeling thus greater security under the river, Sir John decided to allow me to commence the work at other points.

A shaft, 18 feet in diameter, was commenced at Sudbrook, on the centre line, directly opposite the