Emstunnel A 31

Through the Emsland motorway, a fast link between the East Friesian district and the economic centre of Emden, the economically important Ruhr District and the neighbouring Netherlands was set up. At the intersection point, the Ems is some 360 m wide between the banks of the dike forelands. Along the tunnel route, largely cohesive and peaty deposits with occasional layers of fine sand are to be encountered down to a depth of - 6 m below sea level. In the western foreland, a small channel down to - 21 m below sea level exists. Below the Holocene layers, there are Pleistocene deposits comprising fine and medium sands down to a depth of - 30m below sea level, which contains intrusions of Lauenburg clay and peat at their eastern end. Following thorough investigations, including the examination of environmental influences, the effect on shipping and alterations to the river bed, the most favourable method for the trough section emerged as cut-and-cover with an escarped excavation and lowering of the groundwater. The trough was provided with a sufficiently thick base and wing plates protruding at the sides to prevent uplift. For the tunnel below the dikes and in the foreland close to the dikes, cut-and-cover was also selected with anchored sheet piling walls and lowering of the groundwater. The base and walls of the tunnel were made of watertight concrete. A soft sealing layer with protective concrete was installed in the roof. For the river section and for the foreland zones close to the river, the floating and submersing method was chosen. 5 tunnel elements were made in a dry dock close to the tunnel route. Work on the river section was hampered by unexpectedly large amounts of ooze. Even although dredger operations were carried out shortly before submerging the elements, considerable amounts of fresh ooze could not be prevented from being deposited in the period following the positioning of the elements. Special methods for clearing the ooze beneath the elements had to be developed so that a safe foundation could be attained.

• Country: Germany
• Region: Niedersachsen
• Tunnel utilization: Traffic
• Type of utilization: Road tunnel
• Client: Bundesrepublik Deutschland
• Main construction method: Open
• Type of excavation: Immersion/Submersion
• No. of tubes: 1
• Tunnel total length: 1453 m, incl. 945 m Tunnel
• Construction start/end: 1984 to 1989