Engineering Wonders of the World
Volume III

160 ENGINEERING WONDERS OF THE WORLD. of its time. The driving of a long tunnel is, even under most favourable conditions, ardu- ous work. Where it has to be prosecuted in the face of difficulties such as those met in the Simplon, the humblest workman becomes an unsung hero, and his chiefs the objects of general and well - deserved admiration. When growth of traffic justi- fies the ex- pense, gallery No. 2 will be enlarged to full section for a double track, which at pres- ent exists only for 500 yards in the mid-tun- nel lay-bye, at which trains can pass one another. Mean- while, it is use- ful in assisting ventil ation, about which something may be added. The two portals, at Iselle and Brieg, are, closed, ex- cept when a train is due, by ISELLE PORTAL TO THE SIMPLON TUNNEL. At present the right-hand entrance only is used for through traffic. {Photo, Messrs. A. G. Brown, Boveri, and Company.) thick canvas curtains and screens, sliding on an iron framework surrounding the entrance. .. .. At the Brieg end two powerful centrifugal 10-foot fans drive air into the tunnel, from which it is exhausted by similar fans at the southern end. The curtains are raised by electricity or by hand. For taking trains through, the tunnel, powerful electric locomotives, which pick up current from duplicate con- ductors attached to the arch Electric Locomotives- crown, are used. The locomo- fives have a weight of 62 tons, and de- velop a maxi- mum of 2,300 horse - power. With a train of 300 tons they traverse the tunnel in eight- een minutes, at an average speed of 42 miles per hour. The cost of the tunnel was about £3,200,000, or £148 per yard run. The work occupied 2,392 days, on each of which an average ad- vance over the whole period of 13 69 feet was made at each face. On days when drilling machines were actually in op- eration, the average was 17’45 feet at each end, or 34*90 feet in all. This exceeded considerably the rate of progress in the Arlberg Tunnel. At the date of the meeting of the galleries, 3,740,000 holes had been drilled by hand and machine, 1,496 tons of dynamite exploded, and 1,229,500 cubic yards of rock exca-