Fahrlachtunnel Mannheim

Intermittent beds of gravel, sand and silt. Groundwater 3.5 to 7.5 m below the land surface. The tunnel is largely located in water and over a length of 184 m is beneath railway tracks. On no account were train services to be disrupted, which also explains the demand for extremely low settlements. The section of tunnel completed by cut-and-cover was executed in a drained excavation. The pit was secured through pile wall profiles and a base plate made of unreinforced underwater concrete. The base plate was anchored on account of the uplift below water. The part of the tunnel completed by mining means was excavated protected by subsoil freezing. This was also carried out with great accuracy with boreholes for the icing process in the shape of a ring undertaken along the tunnel route. In order to ensure that freezing was carried out as economically as possible, a partition was set up in the middle of the tunnel route to divide it. A total of 27,000 m² had to be iced, at the time, the biggest project of its kind in the world. A further special feature was the setting up of an auxiliary tunnel directly beneath the railway tracks with maximum overburden of 2.6 m. This served to feed the water supply for freezing the roof zone, which was located above the groundwater level and for icing the partition as well as measuring the temperature of the frozen cone. Provisional support: 2-layer reinforced shotcrete, 35 cm thick. Final lining: watertight reinforced concrete, 50 cm thick.

• Country: Germany
• Region: Baden-Württemberg
• Tunnel utilization: Traffic
• Type of utilization: Road tunnel
• Client: Stadt Mannheim
• Main construction method: Trenchless
• Type of excavation: excavator
• Lining: Shotcrete
• No. of tubes: 2
• Tunnel total length: 489 m
• Cross-section: 100 m²
• Construction start/end: 1988-1992 (4 years)
• Opening: 1992