Cross passages in soil - ground freezing, segment application, excavation and displacement monitoring for segmental lining / Querschlagherstellung im Lockermaterial - Vereisung, Tübbingsicherung, Vortrieb und Deformationsauswertung für die Tübbingschale

After more than 30 years of planning, construction of the Biel East city bypass started on 3 December 2007. The biggest challenge of this project was tunnel excavation in a zone of soil-like material with a length of 2 × 1,000 m, with extremely heterogeneous and variable geological conditions. The main tunnels were excavated by an earth pressure balance machine (diameter 12.56 m), and the cross passages (every 300 m) were constructed by conventional tunnelling methods with shotcrete support. In zones where fully saturated sands prevail ("Alte Schwemmsande"), brine ground freezing techniques were used. In order to prevent overloading of the main tunnels due to freezing pressures, these were supported by a combination of steel frames and dowel pins. Back analyses based on measured displacements of the segmental lining led to the conclusion that freezing pressures did not develop to the extent anticipated under the given ground conditions.