Engineering Wonders of the World
Volume III

THE GREAT TUNNELS THROUGH THE ALPS. 157 ARCHES FOR SUPPORTING THE the heading, and set to work to bore from ten to twelve holes for the blast- ing charges. Two men at- tend to each drill, one reg- ulating the motor, the other direct- ing the tool and replacing it when worn. TIMBERING OF FALSE TEMPORARY In about a permanent lining at difficult couple of hours the holes have been driven to full depth. They are cleared out carefully, and the dynamite cartridges, fuses, and detonators are inserted. Meanwhile, the drills and all other objects liable to be damaged by flying fragments of rock have been removed outside the danger zone, and the bottom of the heading has been covered with a movable steel flooring to facilitate the shovelling up of the débris. Immediately after the explosion the face is deluged by jets of water to clear the air. A truck having been brought up, the men, armed with pick and shovel, clear away the broken rock, and examine the sides and roof carefully, detaching any loose fragments. The time occupied by an advance—drilling, blasting, and clearing—occupied about five hours, allowing a daily advance of 18 feet. For haulage purposes, locomotives, driven by air compressed to over 1,000 lbs. to the square inch, were used in the headings. As the latter advanced it became necessary to make stations in the tunnel at which the supply of com- pressed air could be replenished. The great average depth below the surface at which the tunnel was to be driven—the extreme being 7,000 feet under Mount Leone— PLACES IN THE SIMPLON TUNNEL. promised very high tempera- tures and dangers from excessive pressure. The strata encoun- tered were of gneiss, mica schist, and limestone. At many points water was struck, and squeezes, due to the hori- zontal direc- tion of the strata,' had to be counteracted by extra thick lining. The greatest troubles fell to the lot of the Italian workmen. At .. £ jj i i Difficulties a distance of 4,400 odd kilo- encountered. metres (2’728 miles) from the Iselle entrance, the advanced gallery entered, in November 1901, very rotten ground, out of which cold water poured in enormous quantities at very high pressure, and drove back the miners. Simultaneously, the rock began to crush in the timbering. As soon as the flow had diminished sufficiently the miners proceeded to excavate by hand, and insert frames built of stout timber balks to protect the wagon way. These frames were, however, crushed like matchwood by the enormous pressure, and the heading closed. The engi- neers at once ordered frames of rolled steel beams having webs 16 inches deep and flanges 6 inches wide, to each side of which were bolted massive pitch pine balks 20 inches square. Even these could, not resist the squeeze, and were seriously deformed, but by filling the spaces between the frames with quick-setting cement a secure path was formed for the advance beyond. Though this troublesome portion had a