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Car park caverns beneath Swiss castle 22 Nov 2018

Patrick Reynolds for TunnelTalk

Large parking garage caverns beneath a castle mount in Switzerland have been completed.

Roadheader excavation for Thun car garage, Switzerland
Roadheader excavation for Thun car garage, Switzerland

The Marti Group performed the design-build project to create more than 300 parking spaces in a large span underground vaults below the historical building for the client Parkhaus Thun AG. The project lasted almost five years from the client’s early planning and construction through to the official opening in November.

Excavation using a 130 tonne Eickhoff ET480 roadheader with a transverse cutter began in early 2016 to open up the access tunnels and then the two main parking caverns, which are 80m long x 15m wide x 17m high, and three transverse caverns.

Tunnelling took about 18 months in the mostly molasse geology that comprised conglomerate with some sandstone and marl. The caverns had minimum rock cover of about 8m and were created by heading and bench staged excavations, and support was shotcrete, mesh and bolts. Groundwater level in the castle mount is slightly below the top heading. Excavations also included creating two escape tunnels and a narrow shaft was opened to the surface in the centre of town to help support materials delivery and construction logistics. The escape tunnels and shaft were excavated by a hydraulic excavator using a jackhammer.

Marti had design-build contract challenge below a castle
Marti had design-build contract challenge below a castle
Thun car garage has two large caverns
Thun car garage has two large caverns

The rock mass was found to be generally strong and stiff, containing only minor discontinuities.

Marti Group members on the project were Marti Tunnelbau AG with Marti AG and Marti Generalunternehmung AG, working together as Marti Schlossberg Joint Venture. Design services were provided by consultant Basler & Hofmann AG. The project manager was Ingenta AG.

Concrete lining at Thun caverns
Concrete lining at Thun caverns
Opening celebration at Thun parking garage
Opening celebration at Thun parking garage

The sealing layer to the concrete lining consists of a waterproofing membrane that is drained in the cavern vault area, above the groundwater level, but at lower levels the membrane is pressure resistant. Self-compacting concrete was used for the lining.

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