Use of artificial ground freezing in three sections of the Düsseldorf subway

With the extension of the Düsseldorf subway system near the main railway station several residential buildings together with busy roads had to be underpassed with small distances between the top of the tunnel and the foundation of the buildings. For the construction of three 40 m long tunnel sections artificial ground freezing was used as temporary tunnel support. The excavation area was 45 m 2 for track 1 and 3 and 96 m 2 for track 4. The frost wall thickness for track 1 and 3 was chosen as 1.5 m and for track 4 as 2.2 m. The tunnel cross sections are partly underneath and partly above the ground water level. Therefore the water content in the quarternary sand and gravel was artificially lifted up to ensure sufficient strength of the frozen soil. The paper describes the measures to increase the moisture content and the strength of the frozen soil. The execution of the hole ground freezing project including temperature and settlement measurements during tunnelling is reported.