Engineering Wonders of the World
Volume III

THE GREAT TUNNELS THROUGH THE ALPS. 155 By 1890 the scheme had advanced so far that Messrs. Sulzer, Brandt, and Brandau, as contractors, handed to the company a definite scheme for carrying through A Convention ,, , , the work. Ims scheme was signed. examined and approved by a commission of independent experts, and on November 25, 1895, a convention was signed between the company and the Italian Gov- ernment, and ratified a few days later by the Swiss Government. Out of the estimated £3,0 40,000 needed for the scheme, over £810,000 was s u b- scribed freely by local bod- ies in the countries prin- cipally con- cerned. The plans finally ac- cepted specified, in the place of the usual A WORKING ENTRANCE TO THE SIMPLON TUNNEL. single large tunnel, two single-track tunnels _ . _ , with their axes 55'8 feet apart, and connected by cross-pas- sages every 200 metres. In the first instance only one tunnel would be made full size, but the headings for both were to be driven simul- taneously, in order to facilitate ventilation and transport. This double-barrelled system, here used for the first time, is advantageous in that the derailment of a train on one track cannot endanger the other track, that either tunnel can be repaired without interfering with the other, and that two small tunnels are much less affected by pressure than a single one of equal total section. Events showed that, had the engineers chosen the single large bore, the Simplon Tunnel could never have reached completion. The gradients adopted were 1 in 500 on the Swiss, and 1 in 143 on the Italian side, these to be connected in the middle of the tunnel by a vertical curve of 10,000 metres radius and 80 metres long. Under the contract, signed on April 15, 1898, the first tunnel was to be ready for traffic within five years and nine months from date, and the sec- ond four years later. Subse- quently the period was ex- tended by one year. Care for the workmen was shown in clauses speci- fying that the working faces should be kept moderately cool and be well ventilated, and that cheap and good lodging and food should be provided. These conditions were observed most loyally by the contractors. Before boring operations began—on August 1, 1898—a most thorough survey of the pass and the surrounding peaks had been made, to determine the direction of the tunnel. At each end a Purveying, sighting-point was fixed from which to pro- ject the centre-line through the tunnel. As the working advanced, sighting stations were added at points in the tunnel itself, at inter- vals of a mile or two miles, to carry the line forward. This part of the work was so accurate that the error in direction amounted