The new 2.7 km-long double-track tunnel through the Bözberg is the largest construction site of the Swiss Railway on the 4-metre corridor between Basel and Chiasso. This project aims to transfer the freight crossing the Alps from road to rail.

Overview of the projects of construction on the 4-metre corridor on the Gotthard route. (Source: SBB)

Conversion of the old, existing tunnel to the safety tunnel.

  • Total length approx. 2.7km
  • Cut-and-cover section (2 pcs.), approx. 45m
  • Soft-ground section approx. 170m
  • Two portal structures und entry-cut
  • TBM drive rock, on 2.5km length, excavated cross-section 12.36m
  • Cross-connections (5 pcs), approx. 40m
  • Conversion of old, existing tunnel to the safety and rescue tunnel, length approx. 2.5km
  • Loose rock drive with minimal overlap
  • Difficult geological conditions in the border area of the Tafeljura und Faltenjura
  • Traversing thermal protected zone Bad Schinznach
  • Sulphate rocks and clay rocks with high spring potential
Reference Sheet

Project description

3D model of junction between cross-connection and double-track tunnel

  • Pre-cut and soft-ground drive:  On the side Schinznach-Dorf and the side Effingen a driven portal to cut-and-cover section with 37m and 45m length joins on.  The south portal results in the weathered Keuper a loose rock section of about 170m, driven up in the crown-heading in the shelter of a pipe screen.
  • Drive rock section:  Shield maschine TBM, drive length 2'516m, Excavated cross-section 12.36m. Double-shell lining with segment support and in-situ-lining. Sealing in the area of the thermal protected zone with pressure-retaining full seal. 
  • Conversion of old, existing tunnel in service and rescue tunnel: Dismantling of the railway technical equipment. Roadway installation for road vehicles. Refurbishment of the old tunnel and connection to the new tunnel with 5 cross-connections. nstallation lighting and overpressure ventilation and locks on the portals.

Soft-ground drive in weathered Keuper-layers

  • The existing Bözberg Tunnel was built by the Swiss North-East-Railways in the years 1871 – 1875.
  • The existing railway tunnel is located on the feed line to the Gotthard Base tunnel, but its dimensions do not meet the minimum requirements (corner height 4m) of the combined transport.
  • The mandate includes the planning of the new tunnel including the link with the existing track, as well as the conversion of the existing old tunnel into a service- and rescue tunnel.

3D Geologic Model

  • The Bözberg Tunnel lies in the boarder area of Tafeljura (north) and Faltenjura (south). The tunnel goes through the Jura's overthrust, a shear zone up to 100m thick with multiple, often branching shear planes.
  • On rocks, limestones, limestone marls, dolomites, clay stones and sulphate-containing rocks (anhydrite) are possible. The latter are known for their high swelling potential.

Amberg Team at Work

  • Amberg Engineering is in charge of the engineering association JV BözbergPlus, which has been commissioned by general contractor Implenia Schweiz AG for executive design (phase 51 / 53)
  • Overall project management IG BözbergPlus
  • Executive design for the subprojects loose rock excavation, cross connections and cladding


Complex geological conditions

  • Loose rock excavation with low overlap and cohesive material
  • Heterogeneous soil conditions in the loose rock section
  • Traversing thermal protected zone Bad Schinznach
  • Traversing rocks with high swelling potentional (anhydrite, Opalinus clay, marl)
  • High swelling pressures in areas with low coverage in loose rock
  • High fire-safety requirements
  • Complex geometry in cross-section and in interfaces to other lots

Innovative approach

  • Analysis of the relevant hazard pictures and design of the support means with FE-models
  • Creation of geology BIM models for coordination between contractor, client and PV
  • Planning of a gentle TBM-excavation and a pressure-retaining full seal
  • Dimensioning of the segments and facing for swelling pressures of up to 2.4MPa
  • Planning a monolithic construction and design using 3D shell models
  • Hot rating for the fire curves HCinc and ISO-834 and fire-tests
  • Creation of 3D models for visualization and coordination purposes

Robust solutions

  • Crown heading under cover of a pipe arch and excavation face support with anchor
  • 2-shell lining with a 2-lining FPO sealing (can be testet and injected)
  • Application of the resistance princible and use of a height-adjustable fixed track (LVT-System)
  • Monolithic connection of inner shell blocks through continuous screw reinforcement
  • Use of PP fibre in the facing concrete to improve the spaling behavior