With the precision of Swiss clockwork
A project of the century which began in several locations at the end of the 1990s is coming to a close with commissioning planned for December 2016. With a deviation of only 0.00014% – or horizontally by 8 cm and vertically by 1 cm – the five sections of the world’s longest railway tunnel connect to form the fastest route through the Alps. The two single-track tunnel tubes with approximately 180 cross passages were built deep in the heart of the mountain with up to 2,300 m of overlying rock.
The tunnel was excavated using special tunnel boring machines measuring more than 400 m in length, whose cutterheads were 8.80 m in diameter, each fitted with 58 special drills, and blasting agents were used.
The tunnel vault made of cast-in-place concrete has to be at least 30 cm thick in all places in order to be able to withstand the extraordinarily high tension and pressure, with the help of steel arches, concrete reinforcement and sprayed concrete. In addition, it has to allow for movement as a result of the construction of soft sections in which it is possible for the mountain to deform. For this purpose, special steel profiles are used which can be pushed together – similar to shock absorbers. Water that collects in the tunnel is drained off by means of a gutter below the tunnel. The anticipated high temperatures in the mountain make it necessary to ensure a continuous exchange of air. The trains driving through are to have a “piston effect” which will force the air out. If this proves to be insufficient, mechanical ventilation systems will be subsequently installed.