Page:Walker (1888) The Severn Tunnel.djvu/256

Rh The cavity round the pipe was closed with concrete and brickwork in cement, and the place made perfectly sound and tight.

Where the fissure crossed the tunnel at right angles, two 15-inch cast-iron pipes were laid side by side under the invert, and were then covered with concrete and brickwork in cement, and an extra thickness of brickwork in cement was put into the tunnel invert.

The point where the water rose in the invert of the tunnel by the lifting of what I have called the last stone gave more serious trouble.

At last, at the suggestion of Sir John Hawkshaw, a wall was built round the hole, and inside it the water was allowed to rise. When it had risen about 4 feet, it remained stationary, as at that height the water escaped by other openings into the side-heading. When the water was stationary the whole of the cavity below the invert was filled up with Portland-cement concrete lowered down a wooden tube. After this had been allowed time to set, a hand-pump was set to work in the top of the hole, and it was found that the concrete had made a perfectly water-tight joint, and the hole was easily pumped dry. The concrete had been kept down to a level of 3 feet below the top of the invert, and on this the invert of the tunnel, 3 feet thick of brickwork in cement, was built, without any water to interfere with the work; and on April 18, 1885, at 8 a.m., the last length of the brickwork of the tunnel was keyed