Simplon was the last of the railway tunnels hacked through the Alps without the use of electric power. The 19.2km tunnel connecting the Swiss and Italian rail networks was bored beneath mountains up to 2,100m high, and often in searing temperatures up to 60degreesC. The excavation between 1898 and 1905 was double the speed of earlier 19th century Alpine tunnels at St Gothard, Mont Cenis and Arlberg. When Simplon's two headings - started at Brieg in Switzerland and Isselle in Italy - were joined in February 1905, the error in direction of the tunnelling was just under one centimetre.
High pressure jets of water from turbines near each portal powered the three pronged, three inch hydraulic drills that advanced through the Alps at an average of 5.4m a day. Two parallel tunnel headings were bored simultaneously, 16.5m apart, allowing air and transport to pass through cross passages. The dangers of trying to ventilate one double track tunnel had already been born out on earlier projects.
High death rates of labourers on earlier Alpine projects prompted an international panel of geological experts to insist on higher safety and welfare standards for the Simplon. Clauses on the safety and welfare of the labourers were 'probably the first expression in modern times of formal concern for the welfare of underground workers', according to Gosta Sandstrom in his book The history of tunnelling.
Outbreaks of cholera, typhoid and smallpox which dogged the St Gothard and Mont Cenis projects did not occur at Simplon largely because of the improved welfare regime. At the end of each working day, the men passed through a unit outside the portal where they bathed and hung their overalls to dry.
The welfare regime may have helped keep the number of deaths down, but the work itself was still dangerous and 39 workers lost their lives in construction accidents.
Tunnelling progressed smoothly for the first three years of the project, but disaster struck in 1901 when tunnellers at the southern end struck decomposed rock. Water at 60degreesC poured through the rotten rock in enormous quantities at very high pressure and nearly caused work to be abandoned. Men waist deep in a sludge of hot water and decomposed schist toiled in vain to drive the headings until frames of rolled steel were constructed to withstand the shifting rock. Driving the heading through the 40m 'pressure zone' took six months and bankrupted the contractors.
The 'guiding technical genius' for the project, Alfred Brandt, died long before the first steam locomotive carrying Swiss rail officials passed through the tunnel in January 1906. It was said he worked almost 24 hours a day to get the project going, but he died of a stroke at 53, just after work on the tunnel began.