U-Bahn-Los H 109- Berlin

The route for the extension of Underground railway line 7 to Spandau City Hall undercuts the Havel at the Juliusturmbrücke through construction lot H 109. The Spandau Citadel with the Julius Tower and the Spandau Lock are located only a few metres from it. In order to protect the historic fortifications set up on wooden piling and to maintain shipping on the Havel - as an important waterway in a south-north direction, the client demanded a construction method without lowering the groundwater and which also enabled river traffic to keep flowing at least on one side during the construction operations. The subsurface - with a sapropel layer of greatly varying thickness running crosswise to the tunnel axis in the vicinity of construction and changing elevations along the route - meant that no earth fill could be undertaken in the river zone - a method that has been used a number of times when undercutting rivers in Berlin. The client's draft proposal called for the caisson construction method, with caissons 4 and 5 in the river zone having to be set down on large bored piles beneath the sapropel layer. The consortium advocated setting these caissons on a deep-sunk caisson 4a - a proposal which was both more advantageous in terms of price and which also meant shorter construction times. Caissons 4a, 4 and 5 were got ready in a dry dock on the River Spree to such an extent that they could be floated to their point of installation even given the limited water depth available on the Havel and Spree. There, they were completed and submerged to reach the planned level.

• Country: Germany
• Region: Berlin
• Tunnel utilization: Traffic
• Type of utilization: Underground, urban and rapid transit
• Client: Land Berlin, Der Senator für Bau- und Wohnungswesen Berlin, Abt. VII (Tiefbau)
• Main construction method: Open
• Type of excavation: Immersion/Sinking
• Tunnel total length: 257.60 m
• Construction start/end: 1977 till 1980