Figure 24. — Thames Tunnel. Section through 

 riverbed and tunnel following one of the break- 

 throughs of the river. Inspection of the damage 

 with a diving bell. (Beamish, A Memoir of the 

 Life of Sir Marc Isambard Brunei.) 



900-foot river section was completed in only 14 weeks. 4 

 The entire work was completed almost without 

 incident in just under a year, a remarkable per- 

 formance for the world's second subaqueous tunnel. 

 I lie Tower Subway at first operated with cylindri- 

 cal cars that nearly filled the 7-foot bore; the cars 

 were drawn by cables powered by small steam 

 engines in the shafts. This mode of power had pre- 

 viously been used in passenger service only on the 

 Greenwich Street elevated railway in New York. 

 Later the cars were abandoned as unprofitable and 



the tunnel turned into a footway (fig. 32). This small 

 tunnel, the successful driving due entirely to Great- 

 head's skill, was the forerunner of the modern sub- 

 aqueous tunnel. In it, two of the three elements 

 essential to such work thereafter were first applied: 

 the one-piece movable shield of circular section, and 

 the segmental cast-iron lining. 



The documentation of this work is far thinner than 

 for the Thames Tunnel. The most accurate source of 

 technical information is a brief historical account in 

 Copperthwaite's classic Tunnel Shields and the Use of 

 Compressed Air in Subaqueous Works, published in 1906. 

 Copperthwaite, a successful tunnel engineer, laments 

 the fact that he was able to turn up no drawing or 

 original data on this first shield of Greathead's, but 

 he presents a sketch of it prepared in the Greathead 

 office in 1895, which is presumably a fair representa- 

 tion (fig. 33). The Tower Subway model was built 

 on the basis of this and several woodcuts of the work- 

 ing .irea that appeared contemporaneously in the 

 illustrated press. In this and the adjacent model of 

 Beach's Broadway Subway, the tunnel axis has been 

 placed on an angle to the viewer, projecting the bore 

 into the case so that the complete circle of the working 

 face is included for a more suggestive effect. This 

 was possible because of the short length of the work 

 included. 



Henry S. Drinker, also a tunnel engineer and author 

 of the most comprehensive work on tunneling ever 

 published, treats rock tunneling in exhaustive detail 

 up to 1878. His notice of what he terms "submarine 

 tunneling" is extremely brief. He does, however, 

 draw a most interesting comparison between the first 

 Thames Tunnel, built by Brunei, and the second, 

 built by Greathead 26 years later: 



1 Unlike tin- Brunei tunnel, this was driven from both ends 

 simultaneously, thi total overall progress thus being 3 feet per 

 shift rather than 18 inches. A top speed of 9 feet per day could 

 meed I- each shield under ideal conditions, 



FIRST THAMES TUNNEL 



Brickwork lining, 38 feet 

 wide by 22) • feet high. 

 120-ton cast-iron shield, ac- 

 commodating 36 miners. 



Workings filled by irruption 

 of riser five times. 



Eighteen years elapsed be- 

 tween start and finish of 

 work. 

 Cost: $3,000,000. 



second thames tunnll 

 (tower subway) 

 Cast-iron lining of 8 fee t 

 outside diameter. 

 -''.-ton. wrought-iron shield, 

 accommodating at most 3 

 men. 



"Water encountered at al- 

 most any time could have 

 been gathered in a stable 

 pail." 



Work completed in about 

 eleven months. 



Cost: $100,000. 



224 



HI II J TIN 24H: CONTRIBUTIONS FROM TUK Ml SI-.I'M OF HISTORY AND TECHNOLOGY 



