Over the years I’d made a mental note of tunnels that wanted to visit. I walked the first shield driven tunnel in the world – The Marc Brunel tunnel under the Thames between Rotherhithe and Wapping, now used by the East London Line of London Underground. I’ve visited the highest railway tunnel in Great Britain – the disused summit tunnel of the Brecon to Merthyr Railway at Torpantau.
Then recently a holiday in Italy provided the opportunity to travel the Simplon tunnel between Brig in Switzerland and Iselle in Italy. For a short time this was the longest railway tunnel in the world, but it was famous in civil engineering circles as a breakthrough just as revolutionary as the Brunel tunnel and both were considered to be cutting edge technology at the time and very exciting ventures.
The original Simplon tunnel now takes the southbound trains from Switzerland. The entrance is not very impressive. Although faced in stone it is over shadowed by the adjacent power house which projects at an angle, and the later Simplon II extends past it on the west side.
The tunnel rises on a gradient of 1 in 500 from the Swiss side to the centre and then falls at a gradient of 1 in 143 to Italy. These gradients were selected to make the tunnel self draining during driving, in fact the 1 in 500 gradient had been chosen because this was what had been used in the Mersey tunnel. The rock is mainly gneiss and mica-schist with pockets of “sugar marble”.
The tunnel is lined throughout with masonry in four different thicknesses depending on the rock pressure. However even this was not enough and at one point 51/2 feet of granite blocks were required. The enormous pressure even caused the solid rock floor to rise and in places a masonry arch invert had to be built.
Simplon I was built as a single line tunnel with a parallel gallery. The gallery provided ventilation for the workings and the proviso was made that the gallery would be enlarged to form a second tunnel when traffic receipts exceeded £3,2188 per mile. This happened fairly quickly and the gallery was enlarged to form Simplon II between 1918-1922.
Experience from previous alpine tunnels had indicated that considerable heat would be encountered. The rock temperature way about 55oC but forced ventilation and cold water sprays reduced this to bearable levels.
The temperature was further reduced when the “Great Spring” was struck. This was cold water that flowed at 6,564 gallons per minute and an initial pressure of 600lbs/in2. Tapping hot springs that caused work to stop on many occasions followed this cold water. In fact two people were scalded to death at the tunnel opening ceremony. The death toll in constructing the tunnel was 60.
Today, this seems incredibly high, but in fact health and welfare of the tunnelers had been a prime consideration and had reduced considerably the numbers killed below that of the St Gothard tunnel construction when 800 had died.
Apart from the two unimpressive portals, the traveller sees nothing but a blank tunnel wall and takes the 12 miles under the Alps for granted, but I’m very happy that I have travelled through it.