ASTRA N1, Zurich northern bypass, cut-and-cover Tunnel Katzensee, retaining walls, foundations, excavation pits

As part of the extension of the Zurich northern bypass to 2x3 lanes, a cover was constructed in the Affoltern-Katzensee area, which reunited the landscape and reduced the noise problem.

The two-tube cut-and-cover tunnel comprises three lanes plus emergency lane in the direction of Bern and four lanes in the direction of St. Gallen plus an acceleration lane from the Affoltern entrance merging directly into the deceleration lane to the Büsisee rest area.

The 580 m long cut-and-cover tunnelKatzensee is a two-span frame construction made of in-situ concrete, with span lengths of 17.52 m and 21.02 m (clearance mass). The slab is prestressed and the foundation consisted of bored piles in the very heterogeneous subsoil.

The construction in phases - partly with separate wall and slab construction, due to the spatial conditions, leaving open and setting back individual gaps in the structure with later closure and the associated participation in the construction phase planning - were especially challenging.

The construction of the cut-and-cover tunnel was carried out under running traffic.

Construction costs: lot 4: CHF 410 million, cover: CHF 70 million.

Phases 21-53 (lot 4), phase 51 (cover: civil engineering plans)

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  • Geotechnical engineering and foundation
  • Roads
  • Traffic engineering


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