Figure 42. — St. Clair Tunnel. View of front of shield showing method of excavation in firm strata. Incan- 

 descent electric illumination was used. 1889-90. MHT model — 1" scale. (Smithsonian photo 

 49260-D.) 



was finally completed in 1904, and is now in use as part 

 of the Hudson and Manhattan rapid-transit system, 

 never providing the sought-after rail link. A splendid 

 document of the Haskin portion of the work is S. D. V. 

 Burr's Tunneling Under the Hudson River published in 

 1885. It is based entirely upon firsthand material and 

 contains drawings of most of the work, including the 

 auxiliary apparatus. It is interesting to note that 

 electric illumination (arc, not incandescent, lights) and 

 telephones were used, unquestionably the first em- 

 ployment of either in tunnel work. 



THE ST. CLAIR TUNNEL 



The final model of the soft-ground series reflects, as 

 did the Hoosac Tunnel model for hard-rock tunneling, 

 final emergence into the modern period. Although 

 the St. (1, 111 I uimel was completed over 70 years ago, 

 it typifies in its method of construction, the basic 

 procedures of subaqueous work in the present day. 

 The Thames Tunnel of Brunei, and llaskin's efforts 

 beneath the Hudson, had clearly shown that by 

 themselves, both the shield and pneumatic systems of 



driving through fluid ground were defective in prac- 

 tice for tunnels of large area. Note that the earliest 

 successful works by each method had been of very 

 small area, so that the influence of adverse conditions 

 was greatly diminished. 



The first man to perceive and seize upon the bene- 

 fits to be gained by combining the two systems was, 

 most fittingly, Greathead. Although he had projected 

 the technique earlier, in driving the underground City 

 and South London Railway in 1886, he brought 

 together for the first time the three fundamental ele- 

 ments essential for the practical tunneling of soft, 

 water-bearing ground : compressed-air support of the 

 work during construction, the movable shield, and cast- 

 iron, permanent lining. The marriage was a happy 

 one indeed ; the limitations of ea< h system were almost 

 perfectly overcome by the qualities of the others. 



The conditions prevailing in 1882 at the Sarnia, 

 < )ntario, terminal of the Grand Trunk Railway, both 

 operational and physical, were almost precisely the 

 s. ■ as those which inspired the undertaking of the 



236 



Hi III UN 240: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



