Across the globe, more and more tunnels (and longer tunnels) are being built. Currently, the longest tunnel in the world is the 57 km (35 mi) long Gotthard Base Tunnel in Switzerland, but this could change in the decades to come with the planned 123 km (76 mi) under-sea tunnel to be built between the Chinese cities of Dalian and Yantai. Every tunnel project is a multi-million dollar investment, and the level of accuracy required for tunnel measurement increases continually. When trains are expected to travel through at a speed of up to 300 kph (186 mph), the planned tunnel’s axis has to be maintained with maximum precision. In the case of tunnel construction in ground water such as with the Elb Tunnel in Hamburg, the giant tunnel boring machine has to be driven into a special watersealed target construction with centimetre precision when finished. The smallest directional error in the heading can lead to considerable technical problems and financial risks when working on critical projects of this magnitude.
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