1900.] 



on the Great Alpine Tunnels. 



427 



Having explained in very general terms some of the difficulties of 

 tunnel construction, we will proceed to the case of the great tunnels 

 through the Alps, and for the purpose of rendering the subject more 

 easily intelligible, the following particulars may be given : — 



Length of tunnel in miles 

 North or east portal above sea-1 



level, feet J 



South or west portal above sea-"l 



level, feet / 



Highest level 



Maximum grade in tunnel per\ 



1000 J 



Maximum height of mountain! 



above tunnel, feet / 



Possible maximum temperature) 



of rock, deg. Fahr / 



St. Gothard. 



Mont Cenis. 



93 

 3639 



3757 

 3788 



5-82 



5598 



S5° 



7-98 

 3766 



4164 



4248 



30 



5428 



85°- 



Arlberg. 



6-36 

 4296 



3998 



4300 



15 



2362 



65° 



Slmplon. 



12-26 

 2254 



2080 

 2314 



7 



7005 

 104° 



Mont Cenis Tunnel. 



The Mont Cenis, or as it is more accurately called, the Frejus 

 Tunnel, is nearly 8 miles in length. It is for a double line of way — 

 width being 26 feet, and height above rails 20 feet 6 inches. The 

 construction is of excellent character, and it is lined throughout with 

 either masonry or brickwork, except for two lengths of 100 metres 

 and 70 metres respectively. In these two lengths solid white quartz 

 was encountered, and two years were occupied in penetrating it. 

 The gallery of direction is straight throughout the actual tunnel, 

 being curved away to the portals. 



The system of setting out will be described in more detail when 

 we come to consider the case of the Simplon, but in passing we may 

 remark one peculiarity which does not attach to the other tunnels, 

 viz. that the gallery of direction on the Italian side is shut off by a 

 massive grating from the railway tunnel, and is occupied by guns 

 and Gatlings and by a detachment of artillery, the French portal 

 being commanded by an armour-plated fort. 



The approaches to the tunnel, both on the Italian and French 

 sides, are severe, amounting to 30 per thousand or 1 in 33 on the 

 former, and 25 per thousand or 1 in 4.0 on the latter. 



Owing to an alteration during construction on the Bardonnechia 

 side, it became necessary to introduce an ascending gradient for about 

 1 kilometre in length at the Italian end of the tunnel, and this has 

 resulted in seriously compromising the ventilation. 



A rough diagram will serve to give an idea of the gradients and 

 the consequent difficulty in working the traffic. 



Trains coming from France with an ascending gradient of 1 in 



2 f 2 



