Engineering Wonders of the World
Volume III

1,56 ENGINEERING WONDERS OF THE WORLD. AN INROAD OF WATER, SIMPLON TUNNEL WORKS. to but 8 inches in the 12|- miles, and that of level to but 3| inches. The calculated length of the tunnel was within half an inch of the actual length! The tunnelling method adopted was to drive the two parallel tunnel headings simul- taneously and “ break up ” from heading No. 1 to roof-level, drive top Tunnelling1, jieaj|ngg waySj and grad- ually excavate to full size,* and timber the works in. readiness for the masons following behind. The cross-passages between the two tunnels were closed, with the exception of that nearest the working face, so that the air forced by powerful centrifugal fans up head- ing No. 1 should return by heading No. 2 at * After penetrating some distance, the contractors aban- doned the top gallery system, and opened out the tunnel from the bottom heading. This gave better ventilation. the inmost point possible. To ensure, further, that the workmen should have plenty of fresh air to breathe, large tubes, 15 inches in diam- eter, were taken to the faces, and through them were directed fine jets of high-pressure water, which induced a powerful draught of air cooled by contact with the water. Also, water sprays were fixed at various points to distribute cold water across the passages and reduce the temperature of the rock. A narrow-gauge railway led from the portals up each heading, to transport men, materials, and débris. The cycle of operations to be performed during every “ lift,” . r xT i -n a Series of or advance, of the drills are ’ Operations. normally as follows:—The drilling machine, carrying three drills, is brought up to the face, fixed tightly by means of a hydraulic ram pressing on the sides of