Rauhebergtunnel
The Rauheberg Tunnel passes through the out riders of the Weserbergland between Göttingen and Münden. The southern part of the tunnel was built by cut-and-cover, the central and northern parts by mining means. The hydrogeological explorations revealed that the northern tunnel section would have to be driven through a joint aquifer with abundant water. A medium to strong water inflow of 10 to 20 l/s was forecast. In the transition zone between Röt and shell lime, the height of the underground water table was predicted to be 60 m above the tunnel base. When the crown drive reached the transition zone between Röt and shell lime, conditions were encountered, which were not defined in the geological forecast:
- A yellow lime layer, some 3 to 4 m thick and with a dip of roughly 12° located between the Röt and shell lime was extremely cavernous and contained great amounts of water.
- The underground water was under very high pressure and hampered driving Operations considerably.
On account of this altered situation, the geological marginal conditions were examined. In this connection, it was shown that:
- In the transition zone between the Röt and shell lime, the underground water table can lie up to roughly 70 m above the tunnel base.
- On account of the high permeability of the shell lime, seasonal fluctuations of up to 40 m occur in the underground water level; these can take place very quickly in conjunction with precipitation.
- In the extreme case, a reference water inflow of 800 to 1,200 l/s was predicted.
Whereas the "draining pipe" system could be retained in the Röt section, the tunnel to the north of the yellow lime zone had to be created as a "watertight pipe”, over a distance of 1.7 km. The excavated cross-section was as much as 171 m². The reference water pressure for the "watertight pipe" lies at between 70 m in the yellow lime zone and 30 m at the northern portal. The vault thicknesses accordingly range from 40 to 60 cm and the base thicknesses between 1.25 and 2.00 m. Each of the 11 m long tunnel blocks - dimensioned for a 70 m column of water - was reinforced by 36 t (vault 10 t and base 26 t) of steel and contains 470 m³ of concrete (vault 170 m³ and base 300 m³). The plastic membrane for additionally sealing the vault was installed roughly 1 m below the horizontal working joint vault/base. The synthetic rubber joint strips set inside seal each block joint independent of the external joint strips in the vault required for sealing the membrane. The concrete base was concreted on a thin PE gliding membrane, which reduces induced stresses and in turn, diminishes the risk of cracks.
- Country: Germany
- Region: Niedersachsen
- Tunnel utilization: Traffic
- Type of utilization: Main-line rail
- Client: Deutsche Bahn AG
- Main construction method: Trenchless
- Type of excavation: Drill & Blast
- Lining: Shotcrete
- No. of tubes: 1
- Tunnel total length: 5210 m
- Cross-section: 124 till 142 m²
- Contract Volume: approx. 128 Mio. DM
- Construction start/end: 1982-1987 (52 months)
- Opening: December 1987