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This April, engineers expect to make a final breakthrough in the west tube of the Gotthard Base Tunnel (GBT), a project to dig a 57km (35-mile) railway tunnel, the world’s longest, beneath the Alps. The east tube breakthrough took place amid much media fuss last August. It might seem logical to assume that Swiss engineers and contractors cutting through the Gotthard Massif started at two ends of the tunnel and worked towards each other, with a keep-your-fingers-crossed moment in the middle. In fact, to cut construction time in half, the tunnel – or more accurately two single-track tubes and a series of other excavations to provide, for example, emergency access – was planned in five separate sections. This involved extensive preparatory work. Not only did engineers need to understand the local geology, essential to deciding whether to bore or blast at different points, but the route of the line had to be meticulously worked out – a survey on an epic scale [see below]. Next, tunnels were built to get construction crews and equipment down to where they were needed so that work could begin on the five sections, known as Erstfeld, Amsteg, Sedrun, Faido and Bodio. The Faido section, for example, was linked to the surface via a 2.7km-long (1.6 mile) ‘adit’, an access tunnel driven towards the works area at a gradient of up to 13 per cent. At Sedrun, access is via 800m-deep vertical shafts. So far it’s worked. The £6.3 billion tunnel is set to open for regular scheduled services in 2017. Passenger trains will be able to travel as fast as 250km/h (155mph) through the tunnels.