A two-kilometer-long drainage tunnel was broken through on Tuesday morning. This marks the end of a long-standing project.
It is the canton of Zurich's most important flood protection project ever: the relief tunnel, which is intended to divert the Sihl into Lake Zurich in the event of extreme flooding in order to protect the lower Sihl valley and the city of Zurich. Since April, the impressive 160-metre-long Delia tunnel boring machine has been working its way from Langnau through the rock of the Zimmerberg to Thalwil.
This machine is more than just a drilling machine - it acts as a kind of moving factory. As it mills a circular tunnel out of the rock, it is simultaneously lined with concrete elements. The result is a completed concrete tube with a diameter of 6.6 meters and a total length of around 2 kilometers.
After seven months of work and the removal of countless tons of rock, "Delia", which has already been used in the Gotthard massif, has now reached the surface again. The final breakthrough took place shortly after 10 a.m.