The rock-boring work was accomplished with an hydraulic perforator, a machine consisting of a hollow steel stem, two and three-fourths inches diameter, carrying on its end the three tempered cutting points. It was operated by a hydraulic engine with a pump pressure ranging from 80 to 120 atmospheres, representing an available force of 22,000 to 26,000 pounds. Dur ing operation water was constantly forced through the hollow stem, and while washing away the debris tended to keep the teeth cool. The teeth biting into the rock wore it away at the rate of about one-third an inch per revo lution, the number of revolutions varying from four to eight per minute according to the hard hess of the rock. From 10 to 12 machines were in operation at each end of the tunnel from the start. When the drills had penetrated to the depth of about five feet they were withdrawn, the dynamite was inserted and fired and the spoil cleared away.
Perhaps thegreatest of all of the difficulties encountered in the prosecution of this work was the influxes of hot water, first on the Swiss and later on the Italian side. Professor Schardt, the official geologist, estimated that the tunnel discharged one billion cubic feet of water dur ing its construction. At times the boiling springs tapped converted the boring into a veri table canal, forcing a suspension of operations for months at a time, uritil the water was got ten under control, pumped out and the walls of the tunnel sufficiently cooled by sprays of ice water to allow the men to resume work. Even then they had to be sprinkled constantly with ice water to enable them to withstand the deadly temperatures. These conditions forced the abandonment of the operations on the Swiss side at a point about six miles distant from the entrance, the necessity for the suspension of operations being materially augmented by a landslide which occurred at Moerel, a point on the Rhone, a short distance above the intake of head-water which supplied the hydraulic force for the power station at Brigue. The work was then carried on from the Italian end and ad vanced regularly at the rate of about 16% feet per day, until 6 Sept. 1904, when a gigantic boiling spring was tapped which discharged into the tunnel a stream of water with a tempera ture of 113° F. at the rate of 1,600 gallons per minute. The rock temperature was forced up to 108° F., and the work had to be stopped until a transverse gallery could be constructed to join the two southern passages so as to allow the hot water to flow out of the-main passage through a lateral canal along its walls. The j temperature was cooled by jets of ice cold water, and after a delay of three months, dur ing which the work of enlargement was accom plished, the heading was pushed forward re sulting in a junction of the northern and south ern tunnels 24 Feb. 1905, allowing the immense
volume of water which had accumulated in the headings of the abandoned north tunnels to flow down through the main south tunnel into the Diveria River.
The machinery installed at both ends of the tunnel was mainly of European manufacture. It consisted of four-stage high-lift centrifugal pumps and hydraulic turbines at the power stations, centrifugal pumps driven by Pelton wheels in the swamped portions of the tunnels; duplicate 12%-foot ventilating fans, which will continue to serve all the requirements of the tunnel under operative conditions, driven by two 200 horse-power hydraulic turbines. High pressure plunger pumps in connection with the hydraulic accumulators, each pair of pumps be ing driven by a Pelton wheel, supplied cold water to 16 Brandt hydraulic borers working at both ends of the tunnel, four at each heading face. The high-lift refrigerating centrifugal pumps were run in series at 950 revolutions per minute, under a pressure of 370 pounds per square inch and supplied water to the re frigerating plant at the rate of 1821 gallons per second. The refrigerating conduit also fur nished power for four ejector pumps and six portable fountain heads located in the traversing galleries. In the beginning steam locomotives were employed for hauling, and steam engines were kept in reserve to be used in case of the failure of the water power; but as the work ad vanced compressed air locomotives were used exclusively at both ends of the borings. The air compressors had a capacity of two and three cubic meters of free air per minute and com pressed air into a reservoir of the tubular bat tery type. The machinery installations at both ends of the tunnel were identical.
A very clear idea of the difference in the amount of time and labor consumed in the bor.
ing of ancient and modern tunnels may be ob tained by comparing the Roman tunnel bored for the purpose of draining Lake Fucino with the Simplon. The former, begun in the reign of Julius Caesar, was completed during that of Claudius 52 A.D. It was three and one-half miles long and passed under the Palatine at a maximum depth of 400 feet. Its construction involved the sinking of 40 vertical shafts and many inclined galleries, requiring the labor of 30,000 men during a period of 11 years. It was the most celebrated work of its kind at that time and still remains in an almost perfect state of preservation.