English: Title: Bulletin - United States National Museum

Identifier: bulletinunitedst2401966unit Year: 1877 (1870s) Authors: United States National Museum; Smithsonian Institution; United States. Dept. of the Interior Subjects: Science Publisher: Washington : Smithsonian Institution Press, [etc. ]; for sale by the Supt. of Docs. , U. S. Govt Print. Off. Contributing Library: Smithsonian Libraries Digitizing Sponsor: Smithsonian Libraries

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Text Appearing After Image: Figure 43.—Rear view of St. Clair shield showing the erectoi arm placing .1 cast-iron lining segment. 1 he three motions ol 1 In- arm—axial, radial, and rotational, were manually powered. (Smithsonian photo 49260-C.) Hudson River Tunnel. The heavy traffic .it this vit.il U.S. Canada rail interchange was ferried incon- veniently across the wide St. Clair River, and the bank and river conditions precluded construction of a bridge. A tunnel was projected by the railway in that year, the time when Haskin's tribulations were at their height. Perhaps because of this lack of prece- dent for a work of such size, nothing was done immediately. In 1884 the railway organized a tunnel . ompany; in 1886 test borings were made in the river- bed and small exploratory drifts were started across from both banks by normal methods of mine tim- bering. I he natural gas, quicksand, -i\^\ water encountered soon stopped the work. It was at this time that the railway's president visited Greathead's Citj and South London workings. The obvious answer to the St. Clair problem la) in the successful conduct of this subway. Joseph Hobson, chiel engineer oi the Grand Trunk and of the tunnel project, in designing a shield, is said to have searched for drawings of the shields used in the Broadway and Tower Sulmavs oi 1868-9, but unable to locate any, he relied to a limited extent on th<- small drawings of those in Drinker's volume. There is no explanation as to why he did not have drawings of the City and South London shield at that moment in use. unless one considers the rather un- likely possibility that (ireathead maintained its design in secrecj. The Hobson shield followed Greathead's as closely as any other, in having a diaphragm with closable doors, but a modification of Beach's sharpened horizontal shelves was also used. However, these functioned more as working platforms than supports for the eai th. I he tna< hine was 21 % feet in diameter, an unprecedented size and almost twice that of Greathead's current one. It was driven by 24 hydraulic rams. Throughout the entire preliminary I Onsideration of the project there was a marked sense of caution that amounted to what seems an almost total lack of confidence in success. Commencement of the work from vertical shafts was planned so that if the tunnel itself failed, no expenditure would have been made for approach work. In April 1888, the PAPER 41: TUNNEL ENCJINEERINt; —A MUSEUM TREATMENT 237

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