THE PROCESS OF BORING MONT CENIS.

Westport Times, Volume VI, Issue 910, 6 January 1872, Page 3

THE PROCESS OF BORING MONT CENIS.

At starting, we should remind the reader " says the " Daily News " that i is a mistake to fancy that the tunnel has been bored on a new principle. This is not so; the great work has been accomplished by means of blasting as it has been used in mining operations for centuries. But it is in tho use of air as a motive power for the perforating tools that the novelty of the Mont Cenis tunnel operations consists. Air was compressed to six atmospheres by means of hydraulic pressure obtained from the mountain streams in. the neighbourhood of the tunnel. The piercing instrument was a steel drill driven by a piston worked itself by compressed air from a movable press. The compressed air was conveyed in a cast-iron tube of 7 - 84 inches inside diameter, and 39 inches thick. It is made in lengths of from six to eight feet. Safety valves were placed in this tube, and when the pressure became more than six atmospheres, air escaped, and was conveyed by other tubes to the scene of operations in the middle of the mountain, and supplied the workmen with fresh air. The quantity of water consumed was 85317 cubic feet per second, there being a fall of H4< feet. The method of operation in order to pierce the rock was as follows :—Seven drills pierced a series of holes in the rock. These holes were about a yard in depth, an inch to three inches in diameter, only the smaller ones were filled with power, the larger were simply made to diminish the resistance ■of tho stone. These seventy holes took frum five to seven hours to perforate, according to the nature of the rock. When the holes had been made they were dried thoroughly by means of blasts of compressed air and then charged. The mines were successively exploded, beginning with those in the centre of the vault. Then the fragments were cleared away in trucks. In the twenty-four hours the progress varied from two yards to two yards aud a half