Engineering Wonders of the World
Volume I

188 ENGINEERING WONDERS OF THE WORLD. MEN AT WORK IN THE THIRTY-SIX CELLS OF THE SHIELD. with his tool held above his head. The increased movement of the frames strained them severely while they were being brought upright after the foot had been pushed forward, as the greater their inclination from the vertical the greater thrust did they exert against the head and foot when forced into a perpendicular position. On September 8, 1826, diluted silt found its way through the shield in such quantities as to cause serious alarm. Its appearance was followed by an inrush of water, which fell into the tunnel in a regular cascade, and the shield was an unnecessary expense ; but those actually engaged below ground realized more plainly every day that, but for the pro- tection afforded by the head and poling boards, they could not possibly have excluded the treacherous water-logged gravel and silt. Isambard, Brunel’s son, had from the first taken a prominent part in the conduct of oper- ations, and had begun to show the genius sub- sequently proved by the Royal Albert Bridge, the Great East- ern steamship, the Box Tunnel, and many other great engin- His energy and resource con- Brunel the Younger. eering works, tributed materially to the progress of the work. The promoters of the tunnel, in their eager- ness to hurry matters, presently decided to put the masons upon piecework. As a result the miners were continually being pressed, and, in order to enable them to keep ahead of the bricklayers, the amplitude of an “ advance ” of the shield was gradually increased, contrary to the desires of Brunel, who realized fully the risks entailed. The miner had eventually to excavate 18 inches ahead of his poling boards—a very difficult task in the case of the upper part of the face covered by his cell, which he must attack A Mistaken Policy. taxed the pumping plant to the utmost. Now was felt the need for a much larger drain than that specified by the directors, to carry away the water under instead of through the tunnel. During the year the various parts of the shield had had to be renewed almost through- out. The replacement operations necessarily caused much delay. Yet, in spite of this and of the indisposition of one engineer after another, the work went steadily forward, and at the end of February 1827 visitors were allowed to visit the works, on payment of a shilling, and see for themselves what progress had been made. Their presence was not appreciated by the miners or engineers, as the ground became worse and worse, and the possibility of an irruption of the river more threatening. When stones, brickbats, and other objects began to come down into the frames, Brunel thought it time to examine the bed of the river by means of a diving-bell. Inspection proved the exist- ence of a hollow in the bed immediately over the shield. The workers at the face actually passed a pipe up into the bell and conversed with its occu- pants ! This fact gave little comfort to Brunel, River Bed inspected.