frame of longitudinal pressure. It could then be 

 screwed forward by the amount of advance, the 

 screws bearing to the rear on the completed masonry. 

 Thus, step by step the tunnel progressed slowly, the 

 greatest weekly advance being 14 feet. 



In the left-hand portion of the model is the shaft 

 sunk to begin operations; here also is shown the bucket 

 hoist for removing the spoil. The V-type steam engine 

 powering the hoist was designed by Brunei. At the 

 right of the main model is an enlarged detail of the 

 shield, actually an improved version built in 1835. 



The work continued despite setbacks of every sort. 

 The financial ones need no recounting here. Techni- 

 cally, although the shield principle proved workable, 

 the support afforded was not infallible. Four or five 

 times the river broke through the thin cover of silt 

 and flooded the workings, despite the utmost caution 

 in excavating. When this occurred, masses of clay, 

 sandbags, and mats were clumped over the opening 

 in the riverbed to seal it, and the tunnel pumped out. 

 I. K. Brunei acted as superintendent and nearly lost 

 his life on a number of occasions. After several sus- 

 pensions of work resulting from withdrawal or 

 exhaustion of support, one lasting seven years, the 

 work was completed in 1843. 



Despite the fact that Brunei had, for the first time, 

 demonstrated a practical method for tunneling in firm 

 and water-bearing ground, the enormous cost of the 

 work and the almost overwhelming problems encoun- 

 tered had a discouraging effect rather than otherwise. 

 Not for another quarter of a century was a similar 

 project undertaken. 



The Thames Tunnel was used for foot and light 

 highway traffic until about 1870 when it was in- 

 corporated into the London Underground railway 

 system, which it continues to serve today. The 

 roofed-over top sections of the two shafts may still be 

 seen from the river. 



A number of contemporary popular accounts of the 

 tunnel exist, but one of the most thorough and 

 interesting expositions on a single tunnel work of any 

 period is Henry Law's .-1 Memoir of the Thames Tunnel, 

 published in 1845-1846 by John Weale. Law. an 

 eminent civil engineer, covers the work in incredible 

 detail from its inception until the major suspension 

 in late 1828 when slightly more than half completed. 

 The most valuable aspect of his record is a series of 

 plates of engineering drawings of the shield and its 

 components, which, so far as is known, exist now here 

 else. These formed the basis of the enkuuecl sec lion 



Figure 17. — Soft-ground tunneling. The sup- 

 port of walls and roof of mine shaft by simple 

 timbering; 16th century. MHT model — 3/ t " scale. 

 (Smithsonian photo 49260-/.) 



of the shield, shown to the right of the model of the 

 tunnel itself. A vertical section through the shield 

 is reproduced here from Law for comparison with 

 the model (figs. 21 and 23). 



THE TOWER SUBWAY 



Various inventors attempted to improve upon the 

 Brunei shield, aware of the fundamental soundness 

 of the shield principle. Almost all bypassed the 

 rectangular sectional construction used in the Thames 

 Tunnel, and took as a starting point a sectional 

 shield of circular cross section, advanced by Brunei 

 in hisoriginal patent of 1818. James Henry Greathead 

 (1844-1896), rightfully celled the father of modern 



218 



BULLETIN 240: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



