The method of artificial ground freezing was employed to ensure stability and waterproofing of the platform and escalator tunnels in the Università station of the Naples underground. The paper presents the temperature histories monitored within the ground during the freezing process. Furthermore, the importance of the mineralogical composition of the ground is discussed and it is shown that the temperatures monitored can be interpreted numerically using the ‘Freeze' code, a thermo-hydraulic software developed at the ETH Zurich. The influence of important parameters, such as the spacing between the freeze pipes, the thermal conductivity of the ground and the time–development of cooling temperatures in the freeze pipes, is investigated and critically discussed in order to gain a better understanding of the thermal behaviour of the ground during artificial freezing with liquid nitrogen. ‘Freeze' software is a powerful tool for analysing field data for cases involving non-constant temperatures within freeze pipes.
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.
Nach über 30‐jähriger Planungsgeschichte erfolgte am 3. Dezember 2007 der Spatenstich zur Umfahrung Biel Ostast. Die größten Herausforderungen stellten die Vortriebsarbeiten im Bereich des Lockermaterials dar. Über eine Strecke von fast 2 × 1.000 m zeigten sich die geologischen Verhältnisse äußerst heterogen und stark wechselhaft. Bei der Herstellung der Haupttunnelröhren kam eine Erddruckschildmaschine (–12,56 m) zum Einsatz. Die in einem Abstand von 300 m angeordneten Querschläge wurden in konventioneller Bauweise mit einer Teilschnittmaschine und Spritzbetonsicherung aufgefahren. In den Bereichen der wassergesättigten Schwemmsande bediente man sich der Bodengefriertechnik, wobei das Solegefrierverfahren zur Anwendung kam. Um die bestehenden Haupttunnelröhren vor einer aus dem Eisdruck entstehenden Überbeanspruchung zu schützen, sah man als Sicherungskonzept eine Kombination aus Schubdübel und Stahlrahmen vor. Rückrechnungen im Hinblick auf die wahrgenommenen Verformungen an der Tübbingschale brachten die Erkenntnis, dass die befürchteten Eisdrücke in der vorherrschenden Geologie nur zu einem geringen Maß auftreten.
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