Engineering Wonders of the World
Volume I

THE THAMES TUNNEL. 191 of March 1836. To the credit of all concerned, the substitution had been made without the occurrence of any disaster more serious than a single case of pinched fingers. The work to be done by the new shield caused occasional explosions in the shield, much to the dismay of the men. But the end was now in sight, and all concerned were deter- mined that nothing should baulk them of the final victory. LONGITUDINAL SECTION OF TUNNEL SHOWING PART FINISHED PREVIOUS TO THE TEMPORARY ABANDONMENT IN AUGUST 1828. Further Inroads by Water. equalled almost exactly that already accom- plished by the old, as the heading wall had been built midway between the sites of the two shafts. A very high tide tested the shield severely on June 21, and proved it to be splendidly de- signed and manufactured. Water caused con- tinual trouble, and broke in three times in the course of twenty weeks, the last invasion oc- curring on March 1, 1838. The old plan of plugging the river-bed with clay was repeated, each time with success. At last the ground became so bad that Brunel forbade the re- moval of poling boards, and gave instructions that they should be forced forward through the silt. The miner had then to dig down behind each board in turn when the advance of that above it had opened a way for his tools. A novel and very unpleasant difficulty now presented itself in the form of sulphuretted hydrogen, smelling like rotten eggs. This poisonous gas caused so much illness among the men that the duration of a “ shift ” had to be greatly curtailed, and the means of ventilation greatly improved. To add to the general discomfort, an inflammable gas entered the workings, and Trouble given by Poisonous Gas. A Curious Subsidence of Ground. any trouble in By April 1840 the shield had passed low- water mark on the north shore, and was within ninety feet of the site of the northern shaft, when an extraordinary subsi- dence of ground took place, leaving a pit in the foreshore 30 feet in diameter and 13 feet deep. The occurrence was not connected, however, with the tunnel, though at the time it created great excitement among the spectators. Brunel had the cavity filled with clay bags, and then turned his attention to the building and the sinking of the second shaft. The latter opera- tion required the greatest care, owing to the proximity of buildings, for damage to which the company was responsible. Taught by ex- perience, Brunel gave this caisson a slightly conical form, to diminish friction, and sank it to full depth—70 feet—without underpinning. In August 1840, when the shield was but sixty feet from the shaft, a driftway was driven right through from the tunnel, and for the first time men passed under the Thames from bank to bank. In honour of the occasion Brunel was knighted by his sovereign. Communica- tion estab- lished under the River. Brunel knighted.