The 57 km Gotthard base tunnel, a part of the New Rail Alpine Crossing Project in Switzerland, is one of the longest rail tunnels in the world. The tunnel has been constructed by deploying some of the most advanced equipment and machinery procured from Leister Technologies. The head of the tunnel was been created with a tunnel boring machine. Afterwards, an external safeguarding shell was applied with shotcrete. The drainage layer was then applied onto the shotcrete and fastened onto the concrete with settling bolts. Discs backed with velcro were fastened at the same time, and support the plastic sealing sheets. These sheets are welded by a giant 2×250 metre long equipment, called the “worm”. Later, these plastic sealing sheets are unrolled with a special device and pressed onto the velcro-backed discs.
The overlaps of the sheets are then welded tightly and permanently using the TWINNY-S welding machines from Leister. The TWINNY-S presses the two sheets together and rises easily and safely during welding. Thus, the welding progresses almost by itself. The contact pressure, welding speed and temperature can be adapted according to the requirement. Despite its small dimensions, welding speeds of up to 2 metres per minute are possible with the TWINNY-S. The tightness is the most important criterion when evaluating the weld quality. To guarantee the greatest possible safety, a test channel is installed for each overlap weld. This is realised with the pressure roller on the TWINNY-S which was specially designed for this purpose.
The structural sealing acts as a shield protecting the tunnel against penetration by mountain water. Drainage pipes collect the diverted moisture on both sides. Further, waterstop profiles set in concrete on both sides in the concrete base complete the rain shield. The rain shield seal is joined to the back of the waterstop using Leister’s lightweight and semi-automatic welding machine TRIAC DRIVE. In addition, Leister’s EXAMO test device was deployed for conducting regular peel tests to check the weld quality.