290 



ENGINEERING. 



doced to 622,000 francs. Three or four thou- 

 sand men are kept busy most of the time on 

 the works, and seventy of the Ferroux pierc- 

 ing-machines are constantly at work. Ihe 

 eight years 1 limit of time within which the 

 work must he completed will be up on Octo- 

 ber 1, 1880, beyond which term the contractor 

 is bound to pay $1,000 per day for six months, 

 $2,000 per day for the next six months, and at 

 the end of the year, if it is not yet finished, to 

 lose every claim as well as his bond of $1,600,- 

 000. The contractor, M. Favre, has therefore 

 sufficient motive to carry it through within 

 the prescribed time, and sufficient energy to 

 do it if it is possible. He is further encour- 

 aged by a bonus of $1,000 to be paid for each 

 day prior to October 1, 1880, after the tunnel 

 is complete. The length of the main tunnel is 

 48,554 feet or 9'19 miles. The difficulties of 

 the work have been vastly greater than was 

 expected, owing chiefly to the hardness of the 

 rock. The miscalculations of the engineers 

 caused a discrepancy of about $20,000,000 be- 

 tween the original estimate and the actual 

 cost, which will be about $55,000,000. The 

 deficit was so great that there was doubt 

 whether it could be raised, until the German, 

 Swiss, and Italian Governments restored con- 

 fidence by granting considerable subsidies. 

 The power by which the drills are worked is 

 compressed air alone, which is compressed out- 

 side and stored up in large reservoirs. The 

 excavated rock is drawn out of the tunnel by 

 locomotives worked also by compressed air, as 

 the use of steam would be impossible. The 

 workmen suffer greatly from the foul air, which 

 is augmented by the explosion of dynamite in 

 the blasts, which is incessant. The exhaust 

 air from the drills alleviates their situation by 

 driving the foul gases toward the mouth of the 

 tunnel. The laborers employed are of Italian 

 nationality, and for the moderate wages of 60 

 cents to $1.25 a day they display great indus- 

 try and endurance in their dangerous and ex- 

 hausting task. Of the three lines which were 

 projected for the St. Gothard Tunnel, the pres- 

 ent one was chosen on account of its being the 

 lowest above the level of the sea, thus afford- 

 ing less danger of snow blockades. The high- 

 est point in the open line is 3,690 feet above 

 the level of the sea, and the highest point in 

 the tunnel 3,785 feet. The original estimate 

 the time required for its completion was 

 fifteen or sixteen years; but Louis Favre, who 

 was the lowest bidder at $196.40 per foot of 

 tnnnel complete, agreed to deliver the works 

 in eight years, expecting to make more profit 

 from the premium offered for advanced com- 

 pletion than from the work itself. The tunnel 

 the mountain on the north, near the 

 village of Goeschenen in the canton of Uri. 

 The elevation at this entrance is 3,637 feet. 

 Ihe WMithern entrance is near the village of 

 Airolo in the canton of Tessin; its height 

 above sea level is 3,756 feet. The tnnnel will 

 i the longest in the world, being 9'19 miles 



in length, while the Mont Cenis Tunnel is 40,- 

 084 feet or 7'6 miles, the Hoosac Tunnel 25,- 

 040 feet or 4'74 miles, and the Sutro 20,370 

 feet or 3 -84 miles in length. The strata of 

 rock pierced have been for the most part 

 gneiss and mica slate, with considerable gra- 

 nitic gneiss and quartz also. The gradient is 

 rising from the northern entrance, 5 -82 feet in 

 1,000 or 30*7 feet per mile, for the distance of 

 24,459 feet, where the height is 3,785 feet 

 above the sea; the line is there level for 590 

 feet, and then descends 1 foot in 1,000 feet, 

 which grade was afterward altered to 2'5 in 

 1,000 or 13-2 feet per mile. The tunnel is 

 made for a double roadway, and is to be 

 arched from one end to the other. 



The plan of tunneling adopted by M. Favre 

 was that usual in France and Belgium of lay- 

 ing the advance drift in the top of the cutting 

 instead of at the bottom, as is the common 

 practice in Germany, Switzerland, and Italy. 

 The advance drift is 8'9 feet square. This was 

 followed by two cuts, the side and the sole 

 cuts. The first, in two segments, one on each 

 side of the axis, followed about 600 feet in the 

 rear of the advance drift, which gave space to 

 the whole width of the arch, and then by a 

 cut on the east wall 12 to 15 feet below the 

 floor of the header, which was worked in two 

 sections, one above and one below ; it was 9'8 

 feet in width. The arches were built as soon 

 as the side-cuts were completed, when the na- 

 ture of the rock seemed to require it, the arch 

 being supported by timbers on one side and 

 by the ramp on the other until the ramp was 

 excavated and the sustaining walls built in. 

 The header is worked with machine-drills, the 

 car carrying six, with eighteen more at hand. 

 The number of holes bored per lineal metre 

 has been from 13 to 20 ; the holes are 1 to 1'2 

 metre deep, or 3'28 to 3'94 feet, and 1-5 inch 

 in diameter. In the granitic gneiss 23 holes 

 in a metre were required, and in mica slate 

 only 14 holes. The McKean, the Winchester, 

 and the Burleigh drills have been used. After 

 the holes are drilled and the car removed 90 

 or 120 feet away, the holes are filled with 7 

 to 12 cartridges each, the cartridge weighing 

 3'1 ounces and containing giant powder. For 

 1 cubic yard of granitic gneiss 8'82 pounds of 

 giant powder was used, but for a yard of mica 

 slate 4-6 pounds. Blasting by electricity was 

 tried, but not found preferable. The upper 

 holes are blasted first, and the under ones last. 

 Little or no tamping has been used. In the 

 side-cuts hand-drilling was employed at first, 

 but afterward machines ; the cars here are for 

 four drills only. The side-cut averages 77 

 square feet. The upper section of the sole cut 

 is about 54 square feet, and the lower one 65 

 square feet. In these a strong car carrying 

 six drills is used. The rest of the tunnel, con- 

 sisting of the arch section of 40'9 to 45-21 

 square feet, the abutment section of 58'13 

 square feet, and the ramp of 207'74, is exca- 

 vated by hand. 



