Tunnel Kieler Förde

Within the scope of the joint energy concept of the Kiel Stadtwerken and the Preußen-Elektra, the part of the city located to the west of the fjord was to be supplied with long-distance heating, originating from the Gemeinschaftskraftwerk Kiel (GKK). The power station is set up on the eastern shore of the fjord. The supply lines pass below the Kiel Fjord in a roughly 1,370 m long reinforced concrete tunnel with an inner diameter of 4.10 m. In addition, 110 kilovolt power cables have been laid in the tunnel. The tunnel essentially runs in a straight line between its end shafts. In its longitudinal section, the depth of the tunnel is governed by the geological state of the Fjord underground, which is characterised by three deep erosion channels in Ice Age deposits. These channels were investigated in a complex subsurface examination programme. They are filled with non-bearing. marine deposits of silt and mud, also sand, to the level of the present fjord bed. Firstly, reinforced concrete shafts were created. They were submersed as caissons under compressed air. The soil was excavated hydraulically or mechanically depending on the various formations and transferred to the surface. For connecting up with the tunnel, the shafts were provided with circular apertures, which were initially closed via steel bulkheads. Hydraulic pipe-jacking was selected as the construction method for the tunnel, with the shaft set up on the eastern shore of the fjord acting as the thrusting shaft. The pipes were produced in a field factory which was established on the eastern construction site. The tunnel was driven using a compressed-air shield with advance hood. This technique made it possible to use various methods for excavating the soil adapted to the cohesive ground formations which were anticipated in the fringe zones of the fjord and the sandy-gravelly formations in its central zone. The cohesive layers of ground were excavated using an excavator with a tear-out force of 30 t and transferred to a settling basin on the surface after being converted into a flushing fluid. During these operations, the working chamber, where the excavator crew members were located, was under compressed air. The maximum operating pressure amounted to 3.0 bar when the non-cohesive ground layers were reached. In the sand/gravel formations, the soil fell to the floor of the shield in a natural slope without any special excavation work being required. It was then hydraulically flushed to the surface, where it was deposited. In the process, it passed through a rotary drum sluice, which permitted grain sizes of up to 12 cm to pass, while retaining larger stones up to 60 cm diameter so that they could be evacuated. In the case of this method, only the area between the face and the front pressure was under compressed air so that no one involved in normal operations was working under compressed air. Only stones with a diameter exceeding 60 cm had to be crushed by hand under compressed air (maximum 3.8 bar) on the spot.

• Country: Germany
• Region: Schleswig-Holstein
• Tunnel utilization: Utilities
• Type of utilization: Tunnel for long-distance heating
• Client: GKK Gemeinschaftskraftwerk Kiel GmbH
• Main construction method: Trenchless
• Type of excavation: Shield machine (SM)?
• No. of tubes: 1
• Tunnel total length: 1368 m
• Cross-section: 5.00 m
• Contract Volume: 38.5 mill. DM
• Construction start/end: 1988-1990 (18 months)
• Opening: 1990