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Main Line Tunnel Berlin, Lot 3, Ramp Structure using the Caisson Method

Crossing the city in a north-south direction in Berlin's central area is an important task in developing its rail links. A 3.5 km long tunnel is being built towards this end. In the zone to the south of the Landwehr Canal, a 230 m long section of the ramp structure had to be constructed using the caisson method joining up with the tunnel built by mining means. Towards this end, 6 caissons measuring up to 60 m in width, 38 m in length and 16 m in height (and a weight of approx. 28,000 t) were created at gaps of 1.5 m and lowered one after the other. They were sunk to a depth of up to 23 m. In order to lower them, the caissons were provided with temporary steel walls set crosswise to the track axis, which were removed following the lowering and the closure phases were completed successfully. The closure phase was carried out protected by slotted walls and sealing bases between the caissons. The average lowering rate for the largest caisson amounted to approx. 0.30 m per working day given an earth volume of 2,300 m³ per metre of sinking depth. Caisson No. 6, which is roughly 1/3rd smaller with an earth volume of 1,500 m³ per metre of sinking depth, was lowered at a daily rate of approx. 0.70 m per working day following the installation of extra pumps. ln order to support the lowering process, the caissons were provided with earth ballast. There was no need for additional water ballast inside the caissons du ring the lowering phase. In addition to ballasting, an 8 cm thick lubrication gap was formed around the caissons to overcome frictional forces. This was continuously grouted with a bentonite-heavy spar mixture during the sinking process. This lubrication gap worked positively as far as reducing the frictional forces and steering the caissons was concerned. The lowering accuracy for the height and the position amounted to below 5 cm.

 

  • Country: Germany
  • Region: Berlin
  • Tunnel utilization: Traffic
  • Type of utilization: Main-line rail
  • Client: Bundesrepublik Deutschland, Land Berlin, Deutsche Bahn AG
  • Main construction method: Open
  • Type of excavation: Immersion/Sinking
  • No. of tubes: 1
  • Tunnel total length: 230 m
  • Diameter (in): 8.93 m
  • Diameter (out): 7.85 m
  • Construction start/end: 1995 till 2004