THE GREAT ALPINE TUNNELS. 



623 



^ecres. J 000 





height of the mountain above the tunnel i.s 5, 428 feet; the temijerature 

 of the rock is greatl}' influenced by this hitter fact. 



The (question of the temperature of the rocks passed through in the 

 construction of a tunnel 



is one of great interest. " '° '^ '' ''' '' ^ eoMecr^ 



as it depends upon sev- 

 eral conditions: (l) The 

 character of the rock; 



(2) the inclination of the 

 beds, those which attain 

 a vertical or nearh^ ver- 

 tical position being less 

 able to confine the heat 

 than those which are 

 more or less horizontal ; 



(3) the height of the 

 mountain above the tun- 

 nel, or. in other words, 

 the thickness of the 

 blanket. 



A diagram is shown 

 (see fig. 5) giving the 

 temperature actually 

 encountered in the St. 

 Gothard and Arlberg 

 tunnels, and from these, 

 aided by the carefully 

 prepared geological sec- 

 tion along the center 

 line of the Simplon Tun- 

 nel, an approximate line 

 (in red) is given of the 

 temperatures which are 

 expected. 



The possibility of 

 cooling the rocks and 

 the air of the tunnel will 

 be dealt with later on, 

 but there is in addition 

 a permanent lowering 

 of the temperature after 

 the tunnel is complete, 

 particulars of which will l)e given under the description of the St. 

 Gothard. 



For each l-t-t feet of superincumbent rock or earth the increase is 

 found to be 1^ F. 





GOT.¥APD • *tf 



■S/MPlOAf 

 70S Afecrey 



Fig. 5.— Curves showing depths corresponding to an increase in 

 temperature of 1° C. for the Mont Cenis, Gothard, and Arlberg 

 tunnels (with curve of probable temperature for the Simploa 

 Tunnel). 



