U-Stadtbahn Essen, Baulos 32/33

The geological conditions in the north of Essen with a high groundwater level, extremely varied heights of the individual layers of soil comprising marl and saturated silts with organic components and mud intrusions, made it necessary to use a shield drive based on the earth-pressure balance principle for the tunnel section and shotcreting under compressed air for the station zone. Two parallel single-track tunnels with a total length of approx. 3.4 km were driven. Extruded concrete was selected as the provisional tunnel support. The EPB shield had a diameter of 7.12 m. The cutting wheel was largely closed in keeping with the method and had two cams at its centre, which were fitted with tools. The flaps which were integrated in the cutting wheel ensured that it could be completely closed. The earth was only discharged when over-pressure prevailed in the earth-pressure chamber. In this way, the face was subject to even pressure during driving, which in turn, meant minimal Settlements. A further important means of reducing settlements was the tunnel lining of 30 cm thick extruded concrete produced in the tail of the shield. It secured the tunnelled cavity. With this method, the concrete is pressed into an annular space at the end of the shield against the surrounding rock through a number of homogeneously filled charging ports. Thanks to the special properties of this highly flowable extruded concrete, the surrounding rock and water pressure are reliably supported even when the concrete is still in liquid state. The high pressure prevailing during the installing of the concrete means that this can be used as a hydraulic press so that disaggregation and relaxation of the surrounding rock resulting from the shield drive can at least partially be compensated again. Through the resultant pre-tensioning of the soil, at the same time, close interlocking of the rock and the concrete outer shell is established as well as ideal bedding for the tunnel tubes. In the station zone, the inner shell is 35 cm thick. It was created with steel fibre pumped concrete. As, however, the steel fibre concrete for the tunnel inner shell was not a generally approved material. Permission was obtained in this particular case in accordance with the pertinent road construction and tunnelling guidelines following intensive pre-tests and approval proceedings.

Country: Germany
Region: Nordrhein-Westfalen
Tunnel utilization: Traffic
Type of utilization: Underground, urban and rapid transit
Client: Stadt Essen
Main construction method: Trenchless
Type of excavation: Shield machine (SM)
Lining: Steel fibrepumped concrete
No. of tubes: 2
Tunnel total length: ca. 3400 m
Cross-section: Outer diameter 7.12 m / Inner diameter 5.82 m
Contract Volume: 187 mill. DM
Construction start/end: 72 months, 1986 till 1991