The tunnel required two methods of excavation due to a split in geology — 1,000m of TBM tunnel were bored through molasse rock, while a 400m conventionally dug section was located in unconsolidated rock. The Robbins Main Beam machine, for contractor Marti Tunnelbau, completed tunnelling in March and was stopped in order to allow the completion of the conventionally excavated tunnel.
"The performance went very well," said Thomas Güggi, Marti Tunnelbau. "It was hard work, but we had a special back-up to apply 360 degree shotcrete in these sections. The design allowed for a 200mm thick wet application using two shotcrete robots for the full length of the tunnel."
The TBM breakthrough marks the completion of the fourth tunnel for the 4.15m diameter Robbins machine, which underwent major refurbishment in 2002. "We are proud the TBM refurbishment was managed in such a short time, and the TBM excavated without any technical interruptions," added Tunnelbau.
The safety gallery runs parallel to Zurich’s Milchbuck Road Tunnel, a heavily used passage that needed to be updated to the country’s modern safety standards. The safety tunnel, for Swiss federal office ASTRA, includes five cross passages currently under construction.
