The compressors at each entrance discharged into a group of four cylindrical receivers of wrought-iron each 5.3 ft. in diameter by 29.5 ft. long, and having a capacity of 593 cu. ft. The cylinders were placed horizontally, the first one receiving the air at one end and discharging it at the other end into the next cylinder, and so on. By this arrangement the air was drained of its moisture, and the discharge from the end receiver into the tunnel delivery pipes was not affected by the pulsations of the compressors. The delivery pipe decreased from 8 in. in diameter at the receiver to 4 ins. in diameter, and finally to 21⁄2 ins. in diameter, at the front.
The drills employed were of various patterns. The first one employed was the Dubois & François “perforator,” in which the drill-bit was fed forward by hand. This was replaced by Ferroux drills having an automatic feed. Jules McKean’s “perforator” was employed at the north end of the tunnel. All of these drills were of the percussion type, and were mounted on carriages running on tracks. Their comparative efficiency was officially tested in drilling granitic gneiss with an operating air pressure of 5.5 atmospheres with the following results:
| Name of Drill. | Penetration Ins. per Min. |
|---|---|
| Ferroux | 1.6 |
| McKean | 1.4 |
| Dubois & François | 1.04 |
| Soummelier | 0.85 |
The heading was excavated by the circular cut method, the holes being driven as follows: Near the center of the heading three holes were first drilled, converging so as to inclose a pyramid with a triangular base. Around these center holes from 9 to 13 others were driven parallel to the tunnel axis. The center holes were blasted first, and then the surrounding holes. From 3 to 5 hours were required to drill the two sets of holes, and from three to four hours were required to remove the blasted rock. The number of holes drilled in removing each of the various parts was as follows:
| Part No. 1 | 6 to 9 |
| Part No. 2 | 6 to 10 |
| Part No. 3 | 2 |
| Part No. 4 | 6 to 9 |
| Part No. 5 | 3 |
| Part No. 6 | 6 to 9 |
| Part No. 7 | 1 |
| Total for full section | 36 to 40 |
Hauling.
—Two different systems were employed for hauling the spoil and construction material in the St. Gothard tunnel. To remove the spoil from parts Nos. 1 and 2 a narrow-gauge track was laid on the floor of the heading, and the cars were hauled by horses, the grade being descending from the fronts. These narrow-gauge cars were dumped into larger broad-gauge cars running on the track laid on the floor of the completed section and hauled by compressed air locomotives ([Fig. 63]). To raise the incoming structural material from the broad-gauge cars to the narrow-gauge cars running on the level above, hoisting devices were employed.
Fig. 62.—Method of Strutting Roof, St. Gothard Tunnel.
