102 



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vators like, for example, the endless chain bucket excavator 

 used on the Central London Ry., and illustrated in Fig. 12. 

 The method also furnishes an excellent opportunity for electric 

 hauling and lighting during construction. 



The English method of tunneling has been used in building 

 the Hoosac, Musconetcong, Allegheny, Baltimore and Potomac, 

 and other tunnels in America. The names of the European 

 tunnels built by this method are too numerous to mention here. 



AUSTRIAN METHOD. 



The Austrian full-section method of tunneling through soft 

 ground was first used in constructing the Oberau tunnel on the 

 Leipsic and Dresden R.R., in Austria in 1837. It consists in 

 excavating the full section and building up the lining masonry 

 from the foundations as in the English, but with the important 

 exception that the invert is built last instead of first in all cases 

 except where the presence of very loose soil requires its con- 

 struction first. A still more important difference in the two 

 methods is that the excavation is carried out in smaller sections 

 and is continuous in the Austrian method instead of alternating 

 with the mason work as it does in the English method. 



PIGS. 86 and 87. Diagrams Showing Sequence of Excavation in Austrian Method 



of Tunneling. 



Excavation. The excavation in the Austrian method begins 

 by driving the bottom center drift No. 1, Fig. 86, rising from 

 the floor of the tunnel section nearly to the height of the 



