Metro Munich, Line U2 East, construction lot 4 - Stations Messestadt-West, Messestadt-East with running tunnels

Line 2 links up with Munich's Neue Messe fairgrounds and the new district of Messestadt-Riem. After the Munich-Riem Airport was closed, work began on the Underground across the former apron and landing runway. The gradient runs 10-14 m beneath the surface through gravels and sands of the Munich Schotterebene and drops in the west to a depth of 23 m connecting with the starting shaft of the next construction section. Lot 4 was erected by cut-and-cover with a sloped excavation. In the process, it dips some 8 to 10 m into the upper groundwater storey. As lowering of the groundwater was neither desired nor permissible in terms of water management, the entire structure was built protected by a narrow sealed trough or on the western boundary to Lot 3 protected by an overcut bored piling wall. The excavation with the above-mentioned dimensions and an excavated volume of approx. 900,000 m³ was the largest ever during the construction of the Munich Underground. The sealing walls were placed on average at a depth of 16 m after a 4 m advance excavation and installed some 80 m into the prevailing tertiary marl. On account of the high bedding density of the quaternary gravel that is present, the major portion of the sealing wall was created by the semicycle method. In order to ensure unimpeded construction progress, the excavation was split up into 6 individual docks so that the following working stages such as advance extraction, creation of the sealing wall, draining of the dock and the concreting work could be carried out one after the other in series. Linking up with the neighbouring Lot 3 tunnel section built by mining means, 1,700 m² of overcut bored piling wall with a diameter of 120 cm was sunk to a depth of up to 24 m in the route section. As the sealed trough crosses the groundwater flow along its entire length from west to east, far-reaching water drainage measures were imperative. In order to reduce the banking up of the groundwater, drainage lines were laid outside the sealed wall, which were connected by means of temporary cross-lines at gaps of 200 m. These cross-lines were replaced by culverts after the final excavation depth was arrived at. After the conclusion of the construction measure, the slotted walls were bored into at distances of 25 or 12.5 m to form seepage slots.

• Country: Germany
• Region: Bayern
• Tunnel utilization: Traffic
• Type of utilization: Underground, urban and rapid transit
• Client: Landeshauptstadt München, U-Bahn-Referat
• Consulting Engineer: U-Bahn-Referat
• Contractor: Bilfinger + Berger Bau AG
• Main construction method: Open
• Type of excavation: trashed excavation pit
• No. of tubes: 1
• Tunnel total length: 1,700 m, including western section 340 m, West Station 220 m, eastern section 690 m, East Station 250m, siding track 220 m
• Contract Volume: 81 mill. DM
• Opening: November 1996