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Unterquerung der Limmat mit dem Gefrierverfahren

As part of the development of the Zurich rapid transit system, a two-track tunnel was driven below the Limmat by mining means using ground freezing. The same applies to the linking single-track tunnel beneath the Neumühlequai, which branches off at a tangent. The main advantages of the ground freezing method were:

  • the river cross-section is kept free as far as possible
  • avoidance of obstructing the main traffic artery
  • no trees had to be felled.

The tunnel below the Limmat is up to 15 m wide and 10 m high. The overburden down to the river bed amounts to 2.5 to 3.5 m. The up to 40 m long freezing pipes were installed through absolutely accurate boring against pressurised groundwater. Heterogeneously composed layers of moraine-like Limmat gravel and lacustrine deposits, which rise pronouncedly until the Neumühlequai is reached, are to be found beneath fill. Moraines, ground moraines and finally the rock surface of freshwater molasses follow at a depth of some 10 to 20 m. The conditions that were encountered differed considerably in certain zones. Pile walls had to be rammed along the tunnel until the lacustrine deposits, which were forecast as watertight in order to reduce the groundwater currents in the Limmat valley gravel. In addition, vibrated sealing material was installed between the walls. On account of the very thin overcapping layers to the river bed, the exchange of heat with the Limmat had to be restricted through boards of polyurethane. The gap between the bottom of the river and these boards was grouted with Colcrete mortar in order to prevent an undercurrent. Before the freezing core could be set up, groundwater currents had to be dammed up through grouted screens above the two single-track tunnels. The temperatures in the frozen core were monitored through a large number of sensors. Ultrasonic measurements were in a position to localise leaks caused by the geological conditions and closed through grouting.

 

 

  • Country: Switzerland
  • Region: Switzerland
  • Tunnel utilization: Traffic
  • Type of utilization: Underground, urban and rapid transit
  • Client: Kanton Zürich und Schweizerische Bundesbahn (SBB)
  • Main construction method: Trenchless?
  • Type of excavation: Ground freezing?
  • No. of tubes: ?
  • Tunnel total length: ?
  • Construction start/end: ?