Engineering Wonders of the World
Volume III

THE GREAT TUNNELS THROUGH THE ALPS. 153 rises 1 in 500, and for the remaining 4 miles to Langen there is a decline of 1 in 66. Work was begun on November 13, 1880. The working parties at the east end encoun- tered hard but waterless rock ; whereas at the west end the material to be pierced was micaceous and fissured, and water caused de- lays which about counterbalanced the greater ease of drilling. Instead of the top heading method used at the St. Gothard, the engineers employed a bottom heading run in advance at rail-level. From this, vertical shafts, or “ break-ups,” were made every 79 feet in the eastern, and every 216 feet in the western portion to the level of the crown of the arch, and top headings then driven both ways above and parallel to the bottom heading. This system made it possible to have 1,500 metres of excavation in hand at once. The tunnel was enlarged to full size and lined in lengths of 20 to 26 feet, the two processes requiring on the average twenty and fourteen days respectively. In section the tunnel was 261 feet wide (maximum), and 18J feet high above the sleepers over a width of 11| feet. The lining varied in thickness from 1| to 4 feet. It was anticipated that the driving would take five full years, and the contract was based on this term, a premium of £80 a day being allowed for every day Quiek Iess f}ian that period occu- Progress. . „ x - . .u pied. But owing to the quicker system of excavation used and to the adoption of the new Brandt drill, the headings met as early as November 13, 1883—the anniversary of the start—and the tunnel was ready for traffic ten months later. The for- tunate contractor therefore earned a premium of many thousands of pounds. To show the advance in the art of tunnel- ling as exemplified by the three big enterprises noticed so far, the following comparative table is of interest :— Tunnel. Length. Time m months. Average advance per day. Cost per yard. Mont Cenis 7| miles 157 2-57 yards £215 6 0 St. Gothard 9| miles 88 6'01 yards £142 13 0 Arlberg . . 6| miles 43 9'07 yards £107 13 0 The Brandt drill, which was used in the Swiss half of the Arlberg Tunnel, and, years afterwards, exclusively for the Simplon Tun- nel, is worthy of more than .. T, J.«. The Brandt passing mention. It diners radically ’ from the percussive drills used previously in being driven by water instead of air, and in boring, not pecking, its way into the rock. The drill stem is hollow, Counterweight THE BRANDT ROCK DRILL, WHICH HAS DONE SO MUCH TO FACILITATE TUNNEL DRIVING. A. rack bar on which the drills are mounted, and which is jammed across the heading by hydraulic ranis. as is also the boring bit. The last is furnished with, three or four teeth, splayed outwards slightly, so as to make a hole somewhat larger than the stem. Two small cylinders, driven by high-pressure water, rotate the drill mandrel holding the drill through worm gearing, five to ten times a minute, and ex- haust the water through a pipe leading down the hollow centre of the drill. This system keeps the drill cool, and washes out the small detritus from the face as fast as it is de- tached. The teeth are worn down quickly by hard rock, but re-forming, sharpening, and re-tempering them is easy work for a skilled smith. The drill is pressed against the face by a hydraulic ram, which gets a purchase on a beam wedged across the heading. The ram