Tl NNKLS THl:<U (ill HAKD I: .. K 



89 



and schistose sandstone. The stratification of the rock was 

 nearly perpendicular to the axis of the tunnel, except at a few 

 points where the strata intersected the axis at angles varying 

 from 35 to 60. 



Excavation. The tunnel was driven exclusively from the 

 ends by means of a drift. The diagram, Fig. 55, shows the 

 order of the excavation, which began by the drift No. 1, whose 

 dimensions were 9.5 X 8.5 ft., its roof reaching the line of the 

 springers of the arch, and its floor being about 3 ft higher than 

 that of the tunnel. With the excavations of the part No. 2, 

 the drift was widened on each side, 

 except at the roof, and the floor of 

 the tunnel was reached. Above the 

 drift, the heading No. 3 was exca- 

 vated, and when the parts No. 4 

 were battered down the excavation 

 of the upper portion of the tunnel 

 section was completed, and the ma- 

 sonry arch of the lining built. The 

 parts No. 5 were afterward re- 

 moved, and the side walls built up 

 from foundations, and the arch un- 

 derpinned. In the middle of the 

 floor, the part No. 6 was excavated, and the culvert built. 



The excavation of the Mont Cenis tunnel was carried on 

 by hand labor up to the year 1861, when the first drilling 

 machine was employed. The drift, when excavated by hand 

 labor, was blasted by means of many charges placed in holes no 

 more than 1 ft. deep, and very close together. When the per- 

 forating machines were first used the same manner of taring 

 numerous shaft-holes was followed, arid the drift was excavated 

 by a circular cut. Near the center 13 holes were driven, which 

 forim-d the first round of blasting; close to sides 1<5 holes were 

 bored on each side for the second round ; 8 holes lielow and 13 

 above the circular cut formed the third round ; and close to the 



i s r 



FlO. 55. niagrittn Showing 8- 

 qnonce of Kxcavatlon In Mont 

 CenU Tunnel. 



