Relief galleries, Lyssbach, Lyss

The current capacity of the Lyssbach conduit running through Lyss is too small, as clearly demonstrated by the recent flooding caused by the conduit overflowing. Investigations have shown that the flood waters can only be combated by digging a relief gallery between Leen and Fulenmatt, and by expanding the Lyssbach conduit.

The gallery will be dug using a 4.75 metre diameter gripper tunnel boring machine. As it passes below the Swiss railway sections, the unconsolidated rock will be fixed by injection. Then, two pipe shield stages will be constructed with 19 pipes. Pipe length 15 m, with a 5 m overlap.

The total contractor agreement awarded to Implenia comprised: Leen inlet structure; approach cutting, secured by auger piles, anchors and shotcrete; underground underpass below the SBB railway line in unconsolidated ground with support from pipe shield and rock injection; gallery excavation with TBM heading, in-situ concrete floor and shotcrete lining.


Specific figures

Order value

CHF 18.4 million

Construction period

2009 - 2012


2503 m

Total excavated surface

17.7 m2